Formate Oxidase, an Enzyme of the Glucose-Methanol-Choline Oxidoreductase Family, Has a His-Arg Pair and 8-Formyl-FAD at the Catalytic Site

Formate oxidase of Aspergillus oryzae RIB40 contains an 8-replaced FAD with molecular mass of 799 as cofactor. The H-1-NMR spectrum of the cofactor fraction obtained from the enzyme indicated that the 8-replaced FAD in the fraction was 8-formyl-FAD, present in open form and hemiacetal form. The oxidation-reduction potentials of the open and hemiacetal forms were estimated by cyclic voltammetry to be -47 and -177 mV vs. Normal Hydrogen Electrode respectively. The structure of the enzyme was constructed using diffraction data to 2.24 angstrom resolution collected from a crystal of the enzyme. His(511) and Arg(554) were situated close to the pyrimidine part of the isoalloxazine ring of 8-formyl-FAD in open form. The enzyme had 8-formyl-FAD, the oxidation potential of which was approximately 160 mV more positive than that of FAD, and the His-Arg pair at the catalytic site, unlike the other enzymes belonging to the glucose-methanol-choline oxidoreductase family.