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.     

Die Entstehung der chemischen Elemente

For 25 years the conception has been well established that the overwhelming majority of chemical elements and their isotopes have been synthesized in stars during the course of stellar evolution, in particular during the advanced stages and in supernova explosions. Until now this general idea has not led to major difficulties or inconsistencies. On the contrary, the theoretical models have been very successful in explaining the observed abundances in meteorites, planets (including the earth), stars (including the sun) and galactic cosmic rays. Our present understanding of nucleosynthesis will be reviewed with special attention given to nucleosynthetic processes in primordial stars and supernovae. We will concentrate primarily on predictions which can be made for relative abundances rather than for absolute abundances, because the latter problem requires evolutionary models of the galaxy which are beyond the scope of this article.