Application of the Rate Theory to Biological Systems

Abstract

ET and AT are the fundamental elementary chemical steps in many biological processes. Consecutive or concerted series of ET reactions through redox centres of transition metal complexes (iron, copper, molybdenum) or organic redox couples (quinones, thiols) thus represent the key steps of photosynthesis (361–363) and the respiratory chain (364). Proton transfer is one of the most important elementary steps in the action of hydrolytic enzymes (361,365) and in the primary photochemical processes in some visual pigments (366). Ligand substitution is important in the binding of substrate molecules to the metal centres in hydrolytic metalloenzymes (361,367), and transfer of heavy molecular groups is finally the dominant elementary process in the reversible uptake of dioxygen, carbon monoxide and other small molecules by myoglobin (mb), hemoglobin (hb), and related compounds (273) (cf. chapter 6). It is therefore of substantial interest to investigate to what extent the theory of elementary rate processes is applicable to biological systems. The systems where the ET chains have been resolved with a reasonable certainty into elementary steps is, however, restricted to ET in the mitochondrial membranes and the primary processes of photosynthesis, and the discussion in the following therefore refers to these systems in particular.