Relaxation studies of enzymes: concentration and pH dependence of isomerization phenomena.

Equations have been developed for the relaxation times for a variety of mechanisms involving enzyme isomerization coupled to proton transfers. The concentration and pH dependences of the relaxation time have been calculated and graphed for a number of representative mechanisms. We find that for most of the mechanisms examined, the relaxation time is not only pH but also strongly concentration dependent. The concentration dependence results from finite perturbations of the hydrogen ion concentration. For the systems tested, the relaxation time shows a clear concentration dependence at enzyme concentrations below 200 microM.