Effect of buffer on kinetics of proton equilibration with a protonable group

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Abstract
The laser-induced proton pulse generates a massive, brief, proton pulse capable of perturbing biochemical equilibria. The time resolution of the monitoring system can follow the diffusion-controlled protonation of specific sites on macromolecular bodies. To apply this method in enzymology, one must first evaluate how the buffer capacity of biochemical systems (substrates and proteins) will affect the observed dynamics. Unlike equilibrium measurements, where buffer is an inert component, in kinetic studies buffer modulates the observed dynamics. This paper analyzes the effect of buffer on the dynamics of protonation in a model system. The experimental technique is described and the mathematical formalism that determines the various rate constants involved in the reaction is introduced. The analysis of the experiments indicates that in buffered solution proton flux is carried by 2 mechanisms: proton dissociation followed by free proton diffusion; collisional proton transfer between small diffusing solutes. How to evaluate the contribution of each pathway to the overall proton flux is demonstrated.
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