Efficiency of muscle contraction. The chemimechanic equilibrium

Although muscle contraction is one of the principal themes of biological research, the exact mechanism whereby the chemical free energy of ATP hydrolysis is converted into mechanical work remains elusive. The high thermodynamic efficiency of the process, above all, is difficult to explain on the basis of present theories. A model of the elementary effect in muscle contraction is proposed which aims at high thermodynamic efficiency based on an approximate equilibrium between chemical and mechanical forces throughout the transfer of free energy. The experimental results described in the literature support the assumption that chemimechanic equilibrium is approximated by a free energy transfer system based on the binding of divalent metal ions to the myosin light chains. Muscle contraction demonstrated without light chains is expected to proceed with a considerably lower efficiency. Free energy transfer systems based on the binding of ions to proteins seem to be widespread in the cell. By establishing an approximate chemimechanic equilibrium, they could facilitate biological reactions considerably and save large amounts of free energy. The concept of chemimechanic equilibrium is seen as a supplementation to the concept of chemiosmotic equilibrium introduced for the membrane transport by P. Mitchell.     

Biomechanical model of the P-type ion pumps of the cell

The mechanisms of the Na/K pump and of the primary Ca pumps of the cell have not yet been clarified. A biomechanical model of these so-called p-type ion pumps is proposed here. It is based on the assumption that the Na ⁺ and Ca ²⁺ ions are occluded by a contracting protein chain cooperating with the ATPase section of the pump. After transfer of the chain into the region of high Na ⁺ or Ca ²⁺ concentration, the ions are released through stretching of the chain by the ATPase. In the backward transfer of the chain, a retrograde transport of Na ⁺ ions is prevented through occlusion of K ⁺ ions by another region of the same chain. In the case of Ca ²⁺ ions, a similar effect is expected from hydrated Mg ²⁺ ions. The two sections of the chain discriminate between the electrical field strength at the surface and the polarizability of the ions. The most likely mechanism for the transfer of the ion-binding chain is considered to involve a thermally induced transition of a pump dimer between two almost equivalent stable orientations in the membrane.     

Alternative crops for sustainable agricultural systems

The lack of suitable and appropriate crops has been a poorly recognized obstacle to the application of sound agroecological practices in some temperate and tropical regions. Cultivation of traditional hybrid crops in inherently hostile environments forces increased managerial and economic expenditures. Selection of ecologically harmonious crops exploits, rather than opposes natural forces. Based in part on US-AID funded research, we have identified three crops suitable for temperate/tropical cultivation. Amaranthus is recognized in Asia and Central and South America as a food crop that can be grown as a leafy vegetable or as a seed grain in mixed croppings. It does well under a wide variety of conditions using established cultural methods. It is nutritious and highly palatable and, in many areas, is well recognized in the market place. Prosopis species (mesquite) leguminous trees occur worldwide in arid and semi-arid areas. As phreatophytes, they are resistant to drought and high temperature extremes and produce abundant yields of edible beanlike pods. Using the beans from the tree, a variety of attractive, marketable food products have been prepared. We have also identified intermediate wheat-grass, a perennial relative of wheat, as an ecologically and economically attractive alternate crop. It is already a well-established range crop; grown for seed, it becomes a useful grain intercrop. The wholegrain or endosperm mill fractions make excellent tasting, appetizing and attractive baked products. Ongoing agronomic studies indicate it is especially suitable for balancing ecologically unstable areas.     

Quecksilbergasfeinreinigung mittels metall- und salzpartikelbelegter Trägermaterialien (G/S-Reaktor) Ökotoxizität von Quecksilber und seiner Verbindungen

Waste and process gases from thermal power and metallurgical plants or such products from alkali-chloride industries contain metallic, inorganic and organic mercury. Widespread processes applied to remove the greatest amount of mercury are absorption and adsorption. Caused by the lowering of the emission limit from 200 to 50 μg/m³ [STP] by national and European legislators, considerable efforts have been made to enhance the efficiency of the main separation units of flue gas cleaning plants by applying the appropriate technological measures. This article is focused on the removal of mercury from waste gases. The state of engineering is described, especially with regard to enhancing the efficiency of separation in the raw gas, in wet, dry and quasi-dry processes as well as in tail-end process units. Specially impregnated ceramic carriers can be used for the selective separation of metallic, inorganic and organic mercury. Amalgamation has been investigated as a possible separation mechanism both experimentally and in theory. Using the ceramic reactor, removal rates for gaseous mercury and its compounds can be achieved which are even lower than 50 μg/m³ [STP]. The technology, the separation mechanisms and the ecological advantages through the use of ceramic reactors are presented in the article as well.     

Ecological impacts on the limpet Lottia gigantea populations: human pressure over a broad scale on island and mainland intertidal zones

Here long-term monitoring data taken at 33 sites in southern and central California coast and islands were used to evaluate the size structure of the large intertidal limpet, Lottia gigantea in restricted-access and in easily accessible intertidal zones that encompass a wide range of ecological variables. Using multi-dimensional analysis of population size structures, we found that sites on islands and strictly protected mainland sites have significantly larger median limpet sizes and a greater range of limpet sizes than unprotected mainland sites, while no pattern occurs in latitudinal or regional comparison of sites. Although intertidal predators such as oystercatchers were not the primary focus of the monitoring efforts, extensive natural history notes taken during sampling visits support the argument that predation was not a primary cause for the size structure differences. Finally, substratum differences were determined not to have biased the observation of larger limpets in protected sites. In regard to human interactions with limpets, we conclude that the degree of enforcement against poaching is the better predictor of limpet size structure than proximity to population centers or visitation to intertidal sites.