Overvoltage and Solid State Kinetics of Reactions at Biological Interfaces. Cytochrome Oxidase, Photobiology, and Cation Transport. Therapy of Heart Disease and Cancer

Abstract

In the past, biological reactions have usually been assumed to be rate-limited by collision of the reacting molecules in solution. However, it is well known that all cells contain solids (particles and membranes). It therefore seems unreasonable to limit oneself to solution processes. One ought to consider the possibility that some biological processes may occur in, or at, the surfaces of solids. Starting from the hypothesis that a biological reaction may be rate-limited by ohmic conduction of electrons across an enzyme particle, or by the Tafel overvoltage equation for conduction across a liquid-solid interface (like an electrode surface), equations for reduction of substrate as a function of time have been derived. These kinetic equations are different from those of mass action theory, and describe the observed behaviour of various biological reactions such as cytochrome oxidase and various photobiological processes, all of which occur at the surfaces of particles or membranes. The correctness of this approach is supported measurements of electron mobilities in some of these biological solids by new techniques (microwave Hall effect and pulsed electron beam) and by the measurement of a low semi-conduction activation energy in cytochrome oxidase. The use of electrode overvoltage theory has also led to a correct prediction of the kinetics of non-equilibrium ion conduction across the cell surface. One then regards the cell surface not as a bag containing a solution, but rather as the surface of a mass of structured or semicrystalline cell water, in which associated or free alkali cations are analogous to valence and conduction electrons respectively in a semiconductor solid.