Apparent oxygen-dependent inhibition by superoxide dismutase of the quinoprotein methanol dehydrogenase.
Methanol dehydrogenase activity, when assayed with phenazine ethosulfate (PES) as an electron acceptor, was inhibited by superoxide dismutase (SOD) and by Mn2+ only under aerobic conditions. Catalase, formate, and other divalent cations did not inhibit the enzyme. The enzyme also exhibited significantly higher levels of activity when assayed with PES under anaerobic conditions relative to aerobic conditions. The oxygen- and superoxide-dependent effects on methanol dehydrogenase were not observed when either Wurster's Blue or cytochrome c-55li was used as an electron acceptor. Another quinoprotein, methylamine dehydrogenase, which possesses tryptophan tryptophylquinone (TTQ) rather than pyrroloquinoline quinone (PQQ) as a prosthetic group, was not inhibited by SOD or Mn2+ when assayed with PES as an electron acceptor. Spectroscopic analysis of methanol dehydrogenase provided no evidence for any oxygen- or superoxide-dependent changes in the redox state of the enzyme-bound PQQ cofactor of methanol dehydrogenase. To explain these data, a model is presented in which this cofactor reacts reversibly with oxygen and superoxide, and in which oxygen is able to compete with PES as an electron acceptor for the reduced species.
Davidson
V L
VL
Department of Biochemistry, University of Mississippi Medical Center, Jackson 39216-4505.
Kumar
M A
MA
Wu
J Y
JY
D000429:Alcohol Oxidoreductases / Q000037:antagonists & inhibitors* / Q000737:chemistry; D003067:Coenzymes / Q000737:chemistry; D004579:Electron Transport; D004789:Enzyme Activation / Q000187:drug effects; D008345:Manganese / Q000494:pharmacology; D010084:Oxidation-Reduction; D010100:Oxygen / Q000494:pharmacology*; D045542:PQQ Cofactor; D010619:Phenazines / Q000494:pharmacology; D011549:Pseudomonas / Q000201:enzymology; D015363:Quinolones / Q000737:chemistry; D013057:Spectrum Analysis; D013482:Superoxide Dismutase / Q000494:pharmacology*
D003067:Coenzymes; D010619:Phenazines; D015363:Quinolones; C028122:5-ethylphenazine; D008345:Manganese; D045542:PQQ Cofactor; D000429:Alcohol Oxidoreductases; C019641:alcohol dehydrogenase (acceptor); D013482:Superoxide Dismutase; D010100:Oxygen