Adrenodoxin stimulated the oxidation of NADPH by 1,4-benzoquinone, catalyzed by NADPH:adrenodoxin reductase. It prevented the enzyme inhibition by NADPH and formed an additional pathway of benzoquinone reduction presumably via reduced adrenodoxin. In the presence of 100–400 μM NADP+, which increased the K m of NADPH, adrenodoxin acted as a partial competitive inhibitor for NADPH decreasing its TN/K m by a limiting factor of 3. K i of adrenodoxin decreased on the NADP+ concentration decrease and was estimated to be about 10−8 M in the absence of NADP+.
