Enzyme activities of fish skeletal muscle and brain as influenced by depth of occurrence and habits of feeding and locomotion

Activities of lactate dehydrogenase (LDH), pyruvate kinase (PK), malate dehydrogenase (MDH) and citrate synthase (CS) were measured in the white skeletal muscle of marine fishes having different depths of occurrence and different feeding and locomotory strategies. There were significant depth-related differences in the two glycolytic enzymes, LDH and PK. LDH activity was most variable, and differed by 3 orders of magnitude between the most active shallow-living species and certain deep-sea fishes likely to have only minimal capacities for active locomotion. Superimposed on the depth-related patterns was a high degree of interspecific variation (up to 20-fold) in enzymic activity among species from any given range of depth of occurrence. Variation of both LDH and PK activities, noted for shallow- and deep-living fishes, seems to be largely accounted for by differences in feeding habits and locomotory performance. Active pelagic swimmers have much higher activities of LDH and PK than, for example, deep-living sit-and-wait predators. Benthopelagic fishes like rattails and the sablefish have the highest activities found among deep-living fishes, suggesting that these species engage in relatively active food-searching behavior compared to most other deep-sea fishes. The activity of CS, an enzyme of the citric acid cycle and an indicator of aerobic metabolism, varied little among species. Thus, the large interspecific variation in glycolytic potential (LDH and PK) among species is not associated with a similar variation in aerobic metabolism of white muscle. The much higher and more variable activity of MDH relative to CS suggests that, in addition to its function in the citric acid cycle, MDH may play an important role in redox balance in fish white muscle. In a comparison of white muscle composition between the shallow- and deep-living species, water content did not differ significantly, but protein content was significantly higher in shallow- than in deep-living fishes (211 and 130 mg g^-1 wet wt of muscle, respectively). The differences in muscle protein content are small relative to the differences between shallow- and deep-living species in LDH, PK and MDH activities. Thus, depthrelated differences in muscle enzymic activity are caused by factors other than enzyme dilution. Enzyme activities (LDH, PK and CS) in brain tissue were relatively constant among species regardless of depth of occurrence or feeding and locomotory habits. Habitat and lifestyle do not seem to influence the demands for overall metabolic function in brain. The utility of muscle enzymic activity data for making predictions about the ecological characteristics of difficult-to-observe, deep-living, fishes is discussed.     

Depth-related enzymic activities in muscle,brain and heart of deep-living pelagic marine teleosts

The activities [units^-1 wet weight tissue] of lactate dehydrogenase (LDH), pyruvate kinase (PK), malate dehydrogenase (MDH) and isocitrate dehydrogenase (IDH) in white skeletal muscle, brain and heart of 24 pelagic teleost fishes were determined. In addition, for several of the foregoing species, citrate synthase (CS) activities were examined in white skeletal muscle. In muscle, the activities of all these enzymes decrease exponentially with increasing minimum depth of occurrence of the species; this decrease closely parallels the decrease in respiratory rate found previously for these same species. The decline in enzymic activity with increasing minimum depth of occurrence is much greater than the decline in body protein content of the whole fishes, suggesting a disproportionately rapid fall in enzyme concentration in comparison to contractile and structural protein concentrations. The similar reductions in activities of both glycolytic (LDH and PK) and citric acid cycle (CS, MDH and IDH) enzymes with depth indicate that both standard and active metabolisms of deeper-dwelling species are reduced relative to shallower-dwelling forms. There is no suggestion of increased anaerobic capacity with depth or in relation to species, occurrence in the oxygen minimum layer. In brain and heart, there is no significant decrease in enzymic activity with increasing minimum depth of occurrence. These two tissues have similar capacities for metabolism in most fishes, when comparisons are based on enzymic activity per gram wet weight of tissue.     

Biochemical indices of aerobic and anaerobic capacity in muscle tissues of California elasmobranch fishes differing in typical activity level

Biochemical indices of aerobic and anaerobic metabolic capacity were measured in white myotomal muscle of eight marine elasmobranch fish species representing a broad range of locomotor performance, and in red myotomal muscle and heart of three of those species. The objectives were to determine if metabolic capacities vary with typical fish activity level, to compare the endothermic mako shark with ectothermic pelagic sharks, and to compare elasmobranchs with teleosts in order to test the hypothesis that elasmobranchs have lower aerobic capacities, metabolic rates, and swimming speeds. In white myotomal muscle, activities of the enzymes citrate synthase (an index of aerobic capacity), pyruvate kinase, and lactate dehydrogenase (LDH, an index of anaerobic capacity) covaried with typical activity level, and the ability to tolerate intracellular acidification (nonbicarbonate buffering capacity) corresponded with LDH activity. Enzyme activities in red muscle and heart did not show a consistent pattern with respect to fish activity. In comparison with ectothermic sharks, the mako shark had greater aerobic and anaerobic capacities in white muscle, but no significant differences were found in red muscle or heart. This pattern has also been found in teleosts. Thus, endothermic fishes elevate the temperature of red muscle, a tissue specialized for high aerobic performance, whereas white muscle biochemical characteristics are adjusted to support high rates of contraction both aerobically and anaerobically. Muscle enzymic activities of elasmobranchs and teleosts with comparable locomotor habits are similar, thus refuting the hypothesis that elasmobranchs are sluggish, with lower metabolic capacities than teleosts.     

Metabolism,enzymic activities and cold adaptation in Antarctic mesopelagic fishes

Several species of Antarctic mesopelagic fishes that have different minimal depths of occurrence but the same environmental temperature were collected in November–December 1983 and in March 1986 between 0 and 1 000 m in the open water near the marginal ice zone in the vicinity of 60°S 40°W (1983) and 65°S 46°W (1986), and oxygen consumption rate (V _{O 2}) and the activity of two metabolic enzymes, lactate dehydrogenase (LDH, an indicator of the anaerobic potential of locomotory muscle) and citrate synthase (CS, an indicator of citric acid cycle activity or aerobic potential), were determined. In four dominant species, whole-individual oxygen-consumption rate (y, ml O₂ individual^–1 h^–1) varied with weight (X, g) according to the equation y=aX ^b, with b values falling between 0.889 and 1.029. The relation of weight-specific LDH activity (y, U g^–1 wet wt) with weight (x, g) was also described by the equation y=aX ^b, with b values varying between 0.229 and 1.025. Weight-specific CS activity declined with weight, with b values from-0.031 to-0.369. V _{2 O}, LDH activity and CS activity all declined markedly with increased species' minimum depth of occurrence (the depth below which 90% of a species' population lives). Comparisons with previous studies on ecologically equivalent species of the California Borderland indicate that depth-related decreases in metabolism are the result of adapted traits of deeper-living species, not declining temperature within the water column. The metabolic rate of Antarctic mesopelagic fishes is approximately twice that of California species at equivalent temperatures; similar rates were found at the normal habitat temperatures of the two groups. Thus, a well-developed compensation for temperature is present in the Antarctic fishes: cold adaptation. Differences in enzymic activity among species, and among different sized individuals of a species are related to differences in metabolic rate and locomotory capacity. Enzymic indices can be used to estimate metabolic rates and evaluate ecological parameters such as predatory strategies and niche separation.     

Depth zonation and metabolic adaptation in Dover sole,Microstomus pacificus,and other deep-living flatfishes: factors that affect the sole

Flatfishes of Monterey Bay, central California, undergo species replacements with increasing depth along a transect from 100 m on the continental shelf down to a depth of 1400 m on the continental slope. The Dover sole, Microstomus pacificus, differs from the other local flatfish species by undergoing an extensive ontogenetic vertical migration, occupying all depth zones at different life stages, and having its maximum spawning biomass in the oxygen minimum zone between 600 and 1000 m. Size-activity relationships and depth-activity relationships for the glycolytic enzyme lactate dehydrogenase (LDH) and for two enzymes associated with aerobic metabolism, malate dehydrogenase and citrate synthase (CS), were examined in white-muscle tissue of shallow-living, deep-living and ontogenetically-migrating species. Scaling coefficients (b) for weight-specific enzyme activity (log activity)=a+b (log wet weight), varied in sign as well as magnitude for fishes living at different depths. In the shallow-living California halibut Paralichthys californicus, LDH scaled positively (0.39) and CS scaled negatively (-0.15) with size, a pattern observed previously for most shallow-water fish species. The permanently deep-living species, the deepsea sole Embassichthys bathybius, differed in that both LDH and CS scaled strongly negative (-2.0 and-1.5, respectively). For the ontogenetically migrating Dover sole Microstomus pacificus, there was a shelf-slope transition. For the shelf specimens (200 m), LDH scaled positive (0.11) and CS negative (-0.29) and for the slope specimens (400 m), LDH scaled negative (-0.65) and CS strongly negative (-0.63). Rex sole, Glyptocephalus zachirus, showed a similar shelf-slope transition. Intraspecific depth-enzyme activity differences were not incremental, but changed abruptly between the continental shelf stations (100 to 200 m) and the continental slope (400 to 1400 m). Based on comparisons with laboratory-maintained individuals, the decline in the metabolic capacity of the white muscle of Dover sole is a phenotypic response to the low food and oxygen conditions of the continental slope. Contrary to expectation, anaerobic capacity (LDH activity) decreased in response to low oxygen conditions, suggesting that in a permanently hypoxic environment such as the oxygen minimum zone the metabolic strategy may be to not incur an oxygen debt that would be difficult to pay back.     

Effects of long-term acclimation to environmental hypercapnia on extracellular acid–base status and metabolic capacity in Mediterranean fish <Emphasis Type="Italic">Sparus aurata</Emphasis>

In the context of future scenarios of anthropogenic CO₂ accumulation in marine surface waters, the present study addresses the effects of long-term hypercapnia on a Mediterranean fish, Sparus aurata. By equilibration with elevated CO₂ levels seawater pH was lowered to a value of 7.3, close to the maximum pH drop expected in marine surface waters from atmospheric CO₂ accumulation. Intra- and extracellular acid–base parameters as well as changes in enzyme profiles were studied in red and white muscles and the heart under both normocapnia and hypercapnia. The activities of pyruvate kinase (PK), lactate dehydrogenase (L-LDH), citrate synthase (CS), malate dehydrogenase and and 3-hydroxyacyl CoA dehydrogenase (HOAD) reflect the pathways and capacity of oxidative processes in metabolism. Long-term hypercapnia caused a transient reduction in blood plasma pH (pH_e) as well as in intracellular pH (pH_i). Compensation of the acidosis occurred through increased plasma and cellular bicarbonate levels. Changes in enzymatic activities, especially the increase in the activity of L-LDH, paralleled by a drop in CS activity in white and red muscles reflect a shift from aerobic to anaerobic pathways of substrate oxidation during long-term acclimation under hypercapnia. The present results suggest that moderate environmental hypercapnia changes the metabolic profile in tissues of S. aurata. Consequences for slow processes like growth and reproduction potential as well as potential harm at population, species and ecosystem levels require further investigation.     

Effects of nutrition and temperature on metabolic enzyme activities in larval and juvenile red drum,Sciaenops ocellatus,and lane snapper,Lutjanus synagris

The metabolic enzyme activities were determined in larvae of red drum, Sciaenops ocellatus, and lane snapper, Lutjanus synagris, to determine the effect of temperature and nutrition on metabolic enzyme activities and to evaluate if metabolic enzyme activities are useful in assessing the feeding condition of larval fish. During experiments conducted during the spring of 1990, lactate dehydrogenase (LDH) activities in both red drum and lane snapper were approximately an order of magnitude lower than values typical for adult fish; LDH and citrate synthase (CS) activities increased during early developmental stages, but nutritional effects were apparent. Clear differences (up to 4-fold) between well-fed and starving fish were evident in both LDH and CS activity in red drum. Differences between well-fed and poorly fed larvae were evident until 9 d after hatching. Lane snapper larvae reared at a 25°C had significantly lower LDH activities than larvae reared at 28°C.     

Metabolic enzyme activities in shallow- and deep-water chondrichthyans: implications for metabolic and locomotor capacity

Biochemical indices of white (WM) and red muscle (RM) aerobic and anaerobic metabolic capacity were measured in 14 species of benthic and benthopelagic chondrichthyans from a depth of ~90 to 2,200 m to evaluate the relationship between metabolic capacity and depth of occurrence, phylogeny, and locomotor mode. Maximal activities of the enzymes citrate synthase, malate dehydrogenase (MDH), lactate dehydrogenase (LDH), and pyruvate kinase (PK) were analyzed in muscle tissue at 10 °C. These were combined with previously published elasmobranch data in order to represent a comprehensive range of depths, phylogeny, and locomotor modes (i.e., benthic, benthopelagic, pelagic). Significant decreases in WM PK and LDH activities and a lack of significant trends in RM enzyme activities with increasing median depth of occurrence (MDO) indicate a depth-related reduction in both burst-locomotor and metabolic capacity. These trends are consistent with the “visual-interactions hypothesis.” Phylogeny and locomotor mode had little influence on enzyme activities compared to MDO, and the present study suggests similar activities in co-occurring demersal sharks and rays. Overall, the present study indicates low metabolic capacities in deep-sea chondrichthyans, which is important to consider when managing deep-sea fisheries.     

Biologie du chinchard de la Mer Noire (Trachurus mediterraneus ponticus)

The carbohydrate and oxidative metabolism of the lateral musculature and of the liver was investigated in two Black Sea fishes. In Trachurus mediterraneus ponticus, muscular work leads to an intensification of glycolysis in the white muscle, and of oxidation in the red muscle as well as in the liver. Extirpation of the lateral red muscle provokes strong disturbances of muscle performance (without affecting the double character of contraction); the glycogen content of the white muscle decreases, while the lactate content of the liver increases. Hypoxic conditions lead, within a short time, to disturbances of the oxidative capacity in the red muscle and in the liver. In Gobius melanostomus, the effects of hypoxy or of muscular work are less pronounced. In isolated mixed muscle strips of Trachurus, contractions lead to a decrease of glycogen content in the red portion only. In isolated red muscle strips, the glycogen content rises during the incubation. These results are interpreted as supporting the hypothesis of a metabolic role of the lateral red muscle in fishes as energy source for the white muscle and as oxidative site for the catabolites of the latter.     

硫化物胁迫对日本沼虾呼吸代谢和能量代谢酶的影响

研究了硫化物暴露后日本沼虾细胞色素氧化酶(CCO)、琥珀酸脱氢酶(SDH)、延胡索酸还原酶(FRD)和乳酸脱氢酶(LDH)4种呼吸代谢酶及能量代谢酶-精氨酸激酶(AK)活性的变化规律.将日本沼虾暴露于0.6 mg·L~(-1)、2mg·L~(-1)的2个硫化物质量浓度组和不含硫化物的对照组水体中,暴露后0、2、12、24、48 h和解除暴露后48 h取肝胰腺和肌肉组织进行酶活性分析.结果显示:肝胰腺和肌肉组织SDH和CCO活性随硫化物质量浓度升高或暴露时间延长而显著降低(P<0.05).FRD、LDH和AK活性随硫化物质量浓度升高或暴露时间延长而显著升高(P<0.05).解除硫化物暴露后48 h,各质量浓度组酶活性与对照组无显著差异.上述酶活性还存在组织差异,肝胰腺呼吸代谢酶活性高于肌肉中相应酶活性,而AK活性与此相反.结果表明,硫化物胁迫导致日本沼虾有氧呼吸代谢减弱,无氧呼吸代谢增强,并动用其能量贮存物质磷酸精氨酸,产生更多ATP以适应外界不良环境.     

Na+-K+-adenosine triphosphatase activities in gills of marine teleost fishes: Changes with depth,size and locomotory activity level

Activities of the primary enzyme responsible for monovalent ion regulation, Na⁺-K⁺-adenosine triphosphatase (Na⁺-K⁺-ATPase), were measured in gills of marine teleost fishes with different depths of occurrence (0 to 4800 m), body weights (a range of five orders of magnitude), and locomotory capacities. Specimens were collected off the coasts of California and Oregon in 1983–1989, and at the Galápagos Spreading Center and 13°N East Pacific Rise hydrothermal vent sites in 1987 and 1988, respectively. Except for two hydrothermal vent fishes, deep-sea species had much lower Na⁺-K⁺-ATPase activities g^–1 gill filament than shallow-living species, indicating that osmoregulatory costs, like total metabolic rate, are greatly reduced in most deep-living fishes. Within a species, the total branchial Na⁺-K⁺-ATPase activity per individual was dependent on size; the average allometric scaling exponent was 0.83. Using published values for oxygen consumption rates, and the total branchial Na⁺-K⁺-ATPase activities as an index of osmoregulatory costs, we estimated the maximal cost (as percent of ATP turnover) for osmoregulation in ten teleosts. Osmoregulatory costs averaged about 10% of total ATP turnover among these species, and maximal costs were no greater than about 20%. The percent costs of osmoregulation did not differ between shallow- and deep-living fishes. The reduced total ATP expenditure for osmoregulation in deep-living fishes is proposed to result from the sluggish locomotory habits of these fishes, not from selection for reduced osmotic coastper se. Thus, the reduced swimming abilities of these fishes lead to lower rates of water flow over the gills and less blood flow through the gills due to reduced demands for oxygen. Consequently, passive flux of water and ions through the gills is much lower than in more active fishes, and osmotic costs are thereby minimized. The relatively high activities of Na⁺-K⁺-ATPase in gills of the two hydrothermal vent fishes suggest that these fishes may be more active and have higher metabolic rates than other deep-sea fishes.     

Protein composition of white skeletal muscle from mesopelagic fishes having different water and protein contents

The consequences for white skeletal muscle of the whole body variation in water and protein content were examined in 11 mesopelagic fishes taken off the coast of Oregon, USA, in 1983. For such muscles, water content varied from 71 to 91% of muscle wet weight, and protein content ranged from 56 to 141 mg g^-1 muscle wet weight, depending on the species. Dilution by increased water content did not account for the decrease in protein content. Total muscle protein was partitioned into soluble (myogen or sarcoplasmic) and insoluble (myofibrillar) components. Both the myogen and myofibrillar components are reduced in muscle with decreased protein content. The activities (units g^-1 wet wt) of white muscle L-lactate dehydrogenase and L-malate dehydrogenase are higher in fishes undergoing diel vertical migration to surface waters than in fishes that either do not migrate or do not migrate to surface waters. The differences in enzyme activities are not due to a general dilution of muscle protein. The actin content of white skeletal muscle was maintained at a relatively constant level in all 11 species examined and was similar to actin levels observed previously in the white skeletal muscle of scombrids and demersal fishes. This conservation of actin content requires species with a reduced muscle protein content to maintain a significant fraction of their total protein as actin. The specific activities of the myofibrillar Mg²⁺–Ca²⁺-activated adenosine triphosphatases of the mesopelagic species are similar in all 11 species studied. Thus, the ratios of proteins in the isolated myofibrils are probably similar. These results suggest that, in species with decreased muscle protein, there is an increase in the non-myofibrillar form of actin.     

Der einfluß der temperatur auf thermostabilität,isoenzym-muster und reaktionskinetik der laktat-dehydrogenase aus fischen

Methodological problems complicate investigations on thermostability of lactate dehydrogenase (LDH). It is difficult to demonstrate a correlation between adaptation-temperature (AT) and LDH thermostability. Heat-inactivation characteristics change completely if diluted or undiluted tissue extracts are heated. In purified LDH (purchased from Boehringer, Mannheim, FRG), additions such as casein, bovine-serum albumin, NADH and pyruvate — even in small concentrations — can alter considerably the degree of heat resistance. It LDH activity is measured as a function of experimental temperature (ET) according to the composition of the actual test mixture (e.g. altered pyruvate concentration), a different temperature optimum is found. If tissue extracts containing unpurified enzymes are used, the accompanying substances act on the enzyme and modify its properties. Thus, possible influence of AT on enzyme properties can be concealed (suppressed, over-emphasized). In Idus idus acclimated to 10° or 20°C, brain, gill, gut and white dorsal muscle reveal identical LDH-isoenzyme patterns. However, liver-LDH shows a pattern dependent on the AT. A total of 11 bands with LDH activity were found. In 10°C fishes, the Isoenzymes 1, 3, 6 and 7 are especially active. However, 20°C fishes show marked activity of Isoenzymes 5 and 8, and a reduced activity of Isoenzyme 7. According to their electrophoretic mobility, the particular isoenzymes of LDH of white dorsal muscle of I. idus or Rhodeus amarus can be clearly distinguished. The ATs 10° or 20°C do not influence the dependence of reaction order on ET: this is not true for the velocity constant.     

Temperature adaptation in eurythermal cod (Gadus <Emphasis Type="Italic">morhua</Emphasis>): a comparison of mitochondrial enzyme capacities in boreal and Arctic populations

Activities of citrate synthase (CS), cytochrome c oxidase (CCO) and the electron transport system (ETS) were investigated in white muscle and liver of laboratory-maintained cod, Gadus morhua, from the North Sea, Norwegian coast and Barents Sea for an analysis of temperature acclimation and adaptation in aerobic metabolism. Cold acclimation within each population led to elevated activities of CS, CCO and ETS in white muscle. In liver, however, only North Sea cod showed cold-compensated CS activities, with CCO and ETS unchanged. In contrast, cold-acclimated Norwegian cod displayed unchanged enzyme activities, and Arctic cod showed elevated activities for CS, but decreased activities for CCO and no change in ETS. Between-population comparisons revealed clear evidence for permanent cold adaptation in white muscle of northern (Norwegian coast and Barents Sea) compared to boreal (North Sea) cod populations, reflected by higher activities of CS, CCO and ETS at the same acclimation temperature. Cold-compensated, mass-specific enzyme activities in liver were found in northern compared to boreal cod for CS and CCO, however, for ETS, after warm acclimation only. When evaluated as capacity in total liver, such activities were only found in northern populations in the case of CS at all temperatures, and for CCO and ETS at 15°C only. Hepatosomatic index (I_H) and liver lipid contents were highest in North Sea cod, with similar I_H but lower lipid contents in cold- versus warm-acclimated animals. An acclimation effect on I_H was found in Norwegian cod only, with higher I_H but unchanged lipid contents in the cold. In conclusion, permanent cold adaptation of muscle aerobic metabolism prevails in cod populations at higher latitudes, which is in line with permanently elevated rates of oxygen consumption observed in a parallel study. These differences reflect higher maintenance costs in cold-adapted versus cold-acclimated cod.     

Beiträge zur Temperaturadaptation des Aales (Anguilla vulgaris)

Previous authors have demonstrated that changes in O₂-consumption of predominant muscle tissue (in vitro) do not account for the variations in O₂-consumption of a resting intact eel induced by differences in adaptation temperature (AT). The present paper is concerned with the metabolism of the eel's lateral muscle. Activity of cytochrome oxidase and succinate dehydrogenase, expressed in terms of O₂-consumption, are higher in the red muscle portion than in the white one (the factors are 6 to 10 and 2 to 3, respectively). In epaxial muscle strips from some 10 cm behind the anus, red muscle tissue comprises between 44% and more than 60% of the total lateral muscle cytochrome oxidase activity, even though, in this region, the relative weight of the red portion makes up only 11 to 14.5% of the total muscle. The red muscle portion is still smaller in the region anterior to the anus, and its total cytochrome oxidase activity (enzyme activity x relative weight) much lower. Cytochrome oxidase activity remains rather unchanged in the white portion of the muscle. Since the metabolism of white muscles is primarily glycolytic, it is remarkable that — with respect to the terminal oxidative metabolism — tissue temperature adaptation in the eel is more pronounced in red muscles than in white ones. In juvenile and adult eels, acclimated to seasonal temperature, the total cytochrome oxidase activity of the white muscle undergoes little change. However, in cold-acclimated adults with extensive pigmentation, aerobic metabolism of red muscles is favoured; this is indicated both by extremely high cytochrome oxidase activity and increased relative muscle weight. Increased aerobic metabolism of red muscle tissue is, therefore, assumed to be important, especially during the winter spawning migration.     

Activities of metabolic enzymes in the deep-water crabsChaceon fenneri andC. quinquedens and the shallow-water crabCallinectes sapidus

The activities of 18 enzymes were measured in gill, hepatopancreas and muscle tissue of the deep-water crabsChaceon fenneri andC. quinquedens and the shallow-water crabCallinectes sapidus collected from the Gulf of Mexico in January 1989. The activities of catabolic enzymes were correlated in general with the known metabolic rates of the three species. Activities were much higher inC. sapidus than inChaceon fenneri andC. quinquedens. In some cases,C. quinquedens had higher activities thanC. fenneri. The activities of enzymes of amino acid metabolism (glutamate dehydrogenase and alanine aminotransferase) were higher inC. quinquedens, which had high hemolymph [ammonia] and ammonia excretion rates. The activity of lactate dehydrogenase (LDH) ofC. fenneri andC. quinquedens were correlated with the two species' abilities to withstand hypoxia. The more hypoxiatolerant species,C. quinquedens, had higher activity of LDH in its muscles than didC. fenneri.     

The effect of pressure on muscle lactate dehydrogenase activity of some deep-sea and shallow-water fishes

The activity of crude muscle lactate dehydrogenase (LDH) of several species of bathypelagic and shallow-water fishes has been measured at pressures between 1 and 578 atm and at temperatures of 15° and 25°C. No relationship has been found between the effect of pressure on enzyme activity and the hydrostatic pressure of the organism's environment. Applied hydrostatic pressure reduced activity at both temperatures. The decrease at 25°C was double the decrease at 15°C in LDH from shallow-water fishes. However, enzymes from 2 bathypelagic fishes showed approximately the same reduction at both temperatures. Thus, the interaction of temperature and pressure was less in deep-sea than in shallow-water fish LDH. Decreasing temperature and increasing pressure would both reduce the activity of LDH. That is, deep-sea conditions are noncompensatory in this instance. It is possible that the dissociation of the effects of temperature and pressure could be an adaptive feature of deep-sea life.This paper is a portion of a thesis submitted to the Graduate School, University of Georgia, in partial fulfillment for the degree of Master of Science.     

The glycogen turnover rate in mackerel muscles

Turnover rate of the glycogen glucose in the lateral trunk muscles and the liver was investigated in ¹⁴C-glucose injected mackerels, Scomber scombrus. High values were recorded for the red-muscle glycogen; the values were about 40 times lower in the white muscle and the liver. Results are discussed in relation to the assumed metabolic function of the red muscle in fishes.     

Distribution of enzymes of glycolysis and gluconeogenesis in fish tissues

Gluconeogenesis in fishes has been demonstrated in whole animals and liver preparations. However, at present, the relative physiological importance of possible substrates such as lactate, pyruvate and amino-acids or the precise sites of gluconeogenesis are unclear. In mammals, gluconeogenesis takes place in the liver and kidney, and the same could occur in fishes although it has been proposed that fish red muscle is also capable of reconverting lactate (derived from white muscle) to glucose. In this present study, the activities of 3 key glycolytic (hexokinase, phosphofructokinase and pyruvate kinase) and 2 key gluconeogenic (fructose diphosphatase and phosphoenolpyruvate carboxykinase) enzymes were investigated in tissues of the rainbow trout Salmo gairdneri, the cod Gadus morhua, and the plaice Pleuronectes platessa in order to elucidate the relative glycolytic/gluconeogenic capacities of the individual fish tissues. The glycolytic enzymes were found in all tissues, the relative potential being skeletal muscle>heart, brain >kidney, gills>liver. The gluconeogenic enzymes were not present in all tissues, and were mainly concentrated in the liver and kidney. Hence the results indicate that the liver, and to a lesser degree, the kidney are the major sites of gluconeogenesis in fishes, and that the process is unlikely to occur in skeletal muscle.     

Metabolic and molecular stress responses of the gilthead seabream Sparus aurata during long-term exposure to increasing temperatures

Tolerance to a changing climate regime and persistence in the natural environment depends on the limited capacity to acclimate to changing temperatures. The present study aimed to identify and characterize thermal limits of the Mediterranean fish Sparus aurata as well as the processes providing heat protection during exposure to high temperatures. Processes studied included heat shock protein expression, protein kinase activity and metabolic adjustments. Molecular responses were addressed through the expression of Hsp70 and Hsp90 and the phosphorylation of stress-activated protein kinases, p38 mitogen-activated protein kinase (p38 MAPK) and cJun-N-terminal kinases (JNKs). Thermal impacts on metabolic capacities were assessed by studying the maximum activities of citrate synthase (CS), malate dehydrogenase (MDH) and 3-hydroxyacyl CoA dehydrogenase (HOAD) as well as pyruvate kinase (PK) and lactate dehydrogenase (L-LDH). The expression of Hsp70 and hsp90 was activated when the fish were exposed to temperatures beyond 20°C. Increased phosphorylation of p38 MAPK and JNKs indicated the parallel activation of MAPK signaling cascades and the potential involvement of MAPKs in the induction of Hsp genes. Exposure to extreme temperatures beyond 24°C caused an increase in the enzymatic activity of PK and LDH indicating an enhanced glycolytic potential.