THE NADH OXIDASE FROM THE THERMOACIDOPHILIC ARCHAEA ACIDIANUS-AMBIVALENS - ISOLATION AND PHYSICOCHEMICAL CHARACTERIZATION

A flavoprotein with NADH oxidising activity (NADH: acceptor oxidoreduc tase) was isolated from the soluble fraction of the thermoacidophilic archaea Acidianus ambivalens. The protein is a monomer with a molecula r mass of 76 kDa and contains FAD as single cofactor. Its activity as NADH:O-2 oxidoreductase is FAD, but not FMN, dependent and yields hydr ogen peroxide as the reaction product. The activity decreases with pH in the range 4.5 to 9.8, and increases with the temperature, as tested from 30 degrees to 60 degrees C. As elicited by EPR, the purified enz yme also acts as an NADH:ferredoxin oxidoreductase. These features are discussed in light of the possible involvement of this protein in the metabolism of this archaea. (C) 1998 Academic Press.