A negative cooperativity between NADPH and adrenodoxin on binding to NADPH:adrenodoxin reductase

• Published in: FEBS letters 1990, Vol.259 (2), p.338-340
• Main Authors: Čénas, Narimantas K., Marcinkevičiene, Jovita A., Kulys, Juozas J., Usanov, Sergey A.
• Format: Article
• Language: English
• Subjects: ADR, NADPH:adrenodoxin reductase; Adrenal Glands - enzymology; Adrenodoxin; Adrenodoxin - metabolism; ADX, adrenodoxin; Analytical, structural and metabolic biochemistry; Animals; Biological and medical sciences; BQ, 1,4-benzoquinone; Cattle; Enzymes and enzyme inhibitors; Ferredoxin-NADP Reductase - metabolism; Fundamental and applied biological sciences. Psychology; Kinetics; Kinetics, steady-state; Mitochondria - enzymology; NADH, NADPH Oxidoreductases - metabolism; NADP - metabolism; NADPH; NADPH:adrenodoxin reductase; Oxidation-Reduction; Oxidoreductases; Substrate binding; TN, turnover number; TN/K m, bimolecular rate constant
• ISSN: 0014-5793; 1873-3468
• DOI: 10.1016/0014-5793(90)80042-H

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 +.