Examination of the conventional assumption of internal equilibrium within the states of a biochemical cycle.

Abstract

If k is a representative internal rate constant between substates of a given biochemical state, and if .alpha. is representative of the rate constants of the biochemical cycle to which the state belongs, then cyclical activity at steady state pulls the substates out of internal equilibrium with each other by a factor or order 1 .+-. O(.alpha./k). For transients or steady isotonic contractions in muscle, the departures from internal equilibrium can be larger than this. The simplifying assumption that internal equilibrium is always maintained between the substates is justified at steady state as a good approximation if k/.alpha. .gtoreq. 100. In muscle contraction at maximum velocity, something like k/.alpha. .gtoreq. 500 is required. This problem is superficially similar to the question, in Eyring''s rate theory, of the extent to which activated complex .fwdarw. products pulls the activated complex out of the assumed equilibrium with reactants.