engleski

Facilitation of enzyme-catalyzed reactions by partial proton transfer: Application to coenzyme-B-12-dependent methylmalonyl-CoA mutase

The degenerate rearrangement of the 3-propanal radical (as a model for the methylmalonyl-CoA-mutase-catalyzed reaction) is an example of a reaction whose barrier is lowered substantially by protonation. Application of the idea of partial proton transfer to this reaction demonstrates that complete protonation is not necessary to obtain a significant amount of proton-induced barrier lowering. We believe that these findings may provide some clue as to the ability of enzymes to catalyze certain categories of reactions. If a reaction is facilitated by protonation and the proton-accepting site is H-bonded to the enzyme, there will be a contribution to the lowering of the barrier made by partial proton transfer. It is possible to view protonation as a “source” of energy for those reactions whose barriers are lowered by it. It would seem curious under such circumstances for nature not to tap this source, at least to some degree. We submit that such a tapping mechanism is provided by partial proton transfer.

BARRIER HYDROGEN-BONDS ; ELECTRON-PARAMAGNETIC-RESONANCE ; COENZYME-A MUTASE ; REARRANGEMENTS ; MECHANISMS ; B12

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