Hydrolytic enzymes in the two North Sea ctenophores Pleurobrachia pileus and Beroe gracilis

Hydrolytic enzyme activities were determined in tissue extracts of the two North Sea ctenophores Pleurobrachia pileus and Beroe gracilis. The following activities were measured in field samples and characterized according to their mean specific activities and their pH optima: protease, aminopeptidase, amylase, N-acetylglucosaminidase, -glucosidase, chitinase, carboxylesterase, phosphatase. Many of the enzyme activities are correlated, indicating their control by the same factors (i.e. nutritional conditions). Differences found between the phosphatase activities and the apparent lack of the chitinolytic system in B. gracilis reflect the differences in body composition and food specialization in both ctenophores, respectively. The low amylase and -glucosidase activities in both ctenophores agree with the low carbohydrate content of their prey. In spite of high carboxylesterase activities, no lipolytic activity was detected in either of the ctenophores. In a laboratory feeding experiment with P. pileus, the enzyme activities increased but did not reach the activities found in the field samples. In B. gracilis, seasonal variations of some enzyme activities are discussed in relation to the seasonal abundance of its prey, P. pileus.     

Metabolic enzymes in coelomic cells (eleocytes) of the polychaete Nereis virens: sex specific changes during sexual maturation

The activities of some enzymes of the intermediary metabolism and the content of soluble protein and carbohydrate (glycogen plus free glucose) were measured in one type of coelomic cells (eleocytes) of the polychaete Nereis virens. Specimens used in this study were collected between 1989 and 1991 in Oosterscheldt Bay, The Netherlands, and divided into six different stages of sexual maturation as determined by the mean oocyte volume. In both sexes, the soluble protein content in eleocytes of immature individuals (11 mg ml^–1 cell vol) increased three-fold. In prespawning N. virens the soluble protein content decreased to less than 2 mg protein ml^–1 cell vol in females but not in males. In both sexes, the carbohydrate content decreased continuously from immature [300 mol glucose equivalent (equiv) ml^–1 cell vol] to prespawning individuals (< 40 mol glucose equiv ml^–1 cell vol). During the time course of maturation, the specific activities (expressed as units mg^–1 protein) of pyruvate kinase, phosphoenolpyruvate carboxykinase, malate dehydrogenase, alanine aminotransferase and glutamate dehydrogenase decreased in both sexes. A transient increase in the specific activities was found for glycogen phosphorylase and aspartate aminotransferase. No major changes were found for hexokinase, lactase dehydrogenase, glucose-6-phosphate dehydrogenase and malic enzyme. Sex specific differences were found for the activities of citrate synthase and isocitrate dehydrogenase, which were higher in males. the specific activities of the latter enzyme increased more than ten-fold in males, but only four-fold in female eleocytes during maturation. In eleocytes of prespawning females, the activities of most enzymes showed extremely high variations not found in prespawning males. For two enzymes of fatty acid catabolism, -hydroxyacyl-CoA dehydrogenase and -hydroxybutyrate dehydrogenase, only traces of activities were detected, suggesting the absence of significant fatty acid catabolism in the eleocytes. Compared to the eleocytes, the body wall tissue showed ten-fold higher activities of phosphofructokinase, whereas the eleocytes displayed higher activities of the amino acid interconverting enzymes glutamate dehydrogenase and alanine aminotransferase and the glyconeogenic enzyme phosphoenolpyruvate carboxykinase. Citrate synthase activities were similar for both tissues. In the coelomic fluid of N. virens, glucose (< 0.1 to 3.5 mM) and d-lactate (0.1 to 4 mM) were present and represent exogenous substrates for the eleocyte metabolism.     

Seasonal variation in total and soluble tissue nitrogen of Pleurophycus gardneri (Phaeophyceae: Laminariales) in relation to environmental nitrate

Seasonal variations in tissue nitrogen (ethanol soluble nitrate and ninhydrin positive substances, as well as total nitrogen) of different thallus parts of Pleurophycus gardneri Setchell and Saunders were monitored simultaneously with ambient seawater nitrate from 1982 until 1984 in Bamfield, Vancouver Island, British Columbia, Canada. A trend of low, nearly zero levels in ambient nitrate typical for the area in late spring and early summer normally contrasts with average nitrate concentrations of 10 mol NO₃ ^- l^-1 in late fall and winter. Total nitrogen content was greater in the perennial thallus parts, stipe and holdfast than in the annual blade and peaked in fall and early winter. The longitudinal thallus distribution of nitrate revealed a distinct and significant concentration of nitrate in the haptera reaching at maximum 8% nitrate-N of the internal total nitrogen. Internal nitrate concentration ranged from 20 to 5 000 times the ambient nitrate concentration in the midrib, and from 40 to 3 100 times in the wing, while the range was greatest with 400 to 14 000 times in the haptera. P. gardneri contained at most about 7 mol NO₃ ^- g fresh wt^-1 in the blade, which corresponds to about 6% of total tissue nitrogen. Ninhydrin positive substances comprised the major portion of the soluble N pool in P. gardneri and showed a pronounced seasonality. Concentrations of ninhydrin positive substances ranged from 20 to 800 g N g fresh wt^-1 in the midrib and in the wing. In the stipe, ninhydrin positive substances varied from 180 to 2 200 g N g fresh wt^-1, and from 250 to 1 200 g N g fresh wt^-1 in the haptera. Evidence is given that (1) the perennial parts, stipe and haptera of P. gardneri contain the majority of nitrogen products independent of season and ontogenetic stage; (2) ninhydrin positive substances are the most abundant internal nitrogen constituents; (3) the low N values in the blade in summer suggest a nitrogen limited growth; and (4) nitrate may not be the predominant external nitrogen source.     

Hydrolytic enzymes in the coelomic cells of the polychaeteNereis virens during sexual maturation

Nereis virens were collected between April 1989 and April 1990 at Yerseke, Oosterscheldt Bay, The Netherlands. Activities of the hydrolytic enzymes arylsulfatase, acid phosphatase, N-acetylglucosaminidase, aminopeptidase, and carboxylesterase were investigated in coelomic cells (elaeocytes) of individuals at different stages of maturation as determined by the time course of oocyte growth. On a protein-content basis, up to ten-fold higher specific activities were present in the elaeocytes compared to the body-wall tissue. Acid phosphatase, N-acetylglucosaminidase, leucine aminopeptidase, and long- and medium-chain esterase increased continuously from the beginning to the later stage of sexual maturation, with a decline in prespawning individuals. Shortchain esterase and acid aminopeptidase did not show corresponding changes. Activities at different maturation stages were similar for males and females, with the exception of arylsulfatase activity, which was sex-specific and almost lacking in male elaeocytes. The high hydrolytic activities present in the elaeocytes as well as the increase in these activities during sexual maturation are in agreement with the function of these cells in phagocytizing muscle fragments (sarcolytes), which arise as a result of drastic histolysis of the body musculature ofN. virens during the process of sexual maturation.