Kinetic studies on hydrogen peroxide-induced inactivation of mutant formate dehydrogenase from Pseudomonas sp. 101 (PseFDH Cys255Ala) suggest a simple bimolecular mechanism for enzyme reaction with the inactivation agent. In the excess of hydrogen peroxide, the decrease in enzyme activity follows first-order kinetics. Therefore, the first-order effective inactivation kinetic constants determined for various FDH forms at a constant H(2)O(2) concentration can be used as a quantitative measure of the enzyme stability. It was shown that two cysteine residues located in the active site formate- and coenzyme-binding domains (Cys145 and Cys255, respectively) make similar contributions to the enzyme stability, while the contribution of Cys354 is insignificant. The inactivation kinetics of wild-type PseFDH, mutant PseFDH Cys145Ser/Cys255Ala, and FDH produced under stress conditions by bacterium Staphylococcus aureus, higher plants Arabidopsis thaliana, and soya Glycine max, was studied. It was found that the stress-induced FDHs are at least 20 times more stable than the nonstress-induced PseFDH from Pseudomonas sp. 101 grown on methanol.
Keywords: formate dehydrogenase; hydrogen peroxide; inactivation; mutant enzyme; stress.