Electrochemical Investigations of the Interconversions between Catalytic and Inhibited States of the [FeFe]-Hydrogenase from Desulfovibrio desulfuricans

摘要

Studies of the catalytic properties of the [FeFe]-hydrogenase from Desulfovibrio desulfuricans by protein film voltammetry,under a H_2 atmosphere,reveal and establish a variety of interesting properties not observed or measured quantitatively with other techniques.The catalytic bias (inherent ability to oxidize hydrogen vs reduce protons) is quantified over a wide pH range: the enzyme is proficient at both H_2 oxidation (from pH > 6) and H_2 production (pH < 6).Hydrogen production is inhibited by H_2,but the effect is much smaller than observed for [NiFe]-hydrogenases from Allochromatium vinosum or Desulfovibrio fructoso-vorans.Under anaerobic conditions and positive potentials,the [FeFe]-hydrogenase is oxidized to an inactive form,inert toward reaction with CO and O_2,that rapidly reactivates upon one-electron reduction under 1 bar of H_2.The potential dependence of this interconversion shows that the oxidized inactive form exists in two pH-interconvertible states with pK_(ox) = 5.9.Studies of the CO-inhibited enzyme under H_2 reveals a strong enhancement of the rate of activation by white light at -109 mV (monitoring H_2 oxidation) that is absent at low potential (-540 mV,monitoring H~+ reduction),thus demonstrating photolability that is dependent upon the oxidation state.