Kinetic analysis of the interaction of nitric oxide with the membrane-associated, nickel and iron-sulfur-containing hydrogenase from Azotobacter vinelandii.
The effects of nitric oxide (NO) on the membrane-associated form of the nickel and iron-sulfur-containing hydrogenase from Azotobacter vinelandii have been investigated. In the presence of H2 and an electron acceptor (turnover conditions), NO acts as a noncompetitive inhibitor vs. methylene blue (Ki = 12 microM). There is no element of competition between NO and H2, implying that the site of NO action is not the H2-activating site of the hydrogenase. When the membrane-associated hydrogenase is incubated under non-turnover conditions, the enzyme is irreversibly inactivated by NO in a time-dependent process. The inactivation is a non-saturable, pseudo-first-order process which is consistent with a direct chemical reaction between NO and the hydrogenase. Kinetic evidence is presented which is compatible with an interaction between NO and a redox-active component other than the H2-activating site on the enzyme. The complex inhibition pattern of NO has been interpreted in terms of two distinct interactions of NO with iron-sulfur centers of the hydrogenase.
Hyman
M R
MR
Department of Biochemistry, University of California, Riverside.
Arp
D J
DJ
D001395:Azotobacter / Q000201:enzymology*; D002462:Cell Membrane / Q000201:enzymology; D006864:Hydrogenase / Q000037:antagonists & inhibitors; D007506:Iron-Sulfur Proteins / Q000378:metabolism*; D007700:Kinetics; D008962:Models, Theoretical; D009532:Nickel / Q000032:analysis; D009569:Nitric Oxide / Q000378:metabolism* / Q000494:pharmacology
D007506:Iron-Sulfur Proteins; D009569:Nitric Oxide; D009532:Nickel; D006864:Hydrogenase