Chemically gated electron transfer. A means of accelerating and regulating rates of biological electron transfer

Long-range protein electron transfer [ET] reactions may be relatively slow because of long ET distance and low driving force. It is possible to dramatically increase the rate of such nonadiabatic reactions by using an adiabatic chemical reaction to activate the system for rapid ET. Three such examples are discussed; nitrogenase, pyruvate:ferredoxin oxidoreductase, and the methylamine dehydrogenase-amicyanin complex. In each example, the faster activated ET reaction is gated (i.e., rate-limited) by the chemical reaction. However, the reaction rate is still orders of magnitude greater than that of the ungated true ET reaction in the absence of chemical activation. Models are presented to describe the mechanisms of activation in the context of ET theory, and the relevance of such chemically gated ET to the regulation of metabolism is discussed.