TABLE OF CONTENTS PT is of major importance in two distinct areas of biochemistry-acid-base catalysis in enzyme activity, and proton coupled electron transfer in bioenergetics. In the former, the PT events are generally highly localized and the critical purpose is to transfer a proton between adjacent groups, for example an active-site amino acid and a substrate. Water is generally excluded from actives sites (except as a reactant), but there are many examples where a chain of water molecules maintains a specific connection to the bulk phase. [80] This may present a polarizable element that can respond to charge shifts associated with the catalytic events, including local PT. Nevertheless, given the generally pairwise nature of PT in active-site chemistry, descriptions of general acid-base catalysis are applicable and some simple relationships might be expected. In contrast, proton transfer in bioenergetics is usually over long distances, the primary purpose being to translocate protons into and across the membrane, e.g. of the mitochondrion, chloroplast or bacterial cell.
An intermediate example, from active-site proton transfer, is the reaction of carbonic anhydrase (CA), where a proton is taken up (or released) as part of the stoi-chiometric turnover:
Somewhat surprisingly, the transport of H + in and out of the active site is the rate-limiting step. [81], [82] PT occurs over a distance of 8-10 and is associated with the regeneration of the active site Zn 2+ ?OH ? complex:
The communication between the zinc-bound water and the...
