Cu2+ and Zn2+ inhibit nitric-oxide synthase through an interaction with the reductase domain.
Cu(2+) and Zn(2+) inhibit all of the NADPH-dependent reactions catalyzed by neuronal nitric-oxide synthase (nNOS) including ferricytochrome c reduction, NADPH oxidation, and citrulline formation. Cu(2+) and Zn(2+) also inhibit ferricytochrome c reduction by the independent reductase domain. Zn(2+) affects all activities of the full-length nNOS and the reductase domain to the same extent (estimated IC(50) values from 9 to 31 microm), suggesting Zn(2+) occupation of a single site in the reductase domain. Citrulline formation and NADPH oxidation by the full-length nNOS and ferricytochrome c reduction by the reductase domain are affected similarly by Cu(2+), with estimated IC(50) values ranging from 6 to 33 microm. However, Cu(2+) inhibits ferricytochrome c reduction by the full-length nNOS 2 orders of magnitude more potently, with an estimated IC(50) value of 0.12 microm. These data suggest the possibility that Cu(2+) may interact with nNOS at two sites, one composed exclusively of the reductase domain (which is perhaps also involved in Zn(2+)-mediated inhibition), and another that includes components of both domains. Occupation of the second (higher affinity) site could then promote the selective inhibition of ferricytochrome c reduction in full-length nNOS. Neither the inhibition by Cu(2+) nor that by Zn(2+) is dependent on calmodulin.
Perry
J M
JM
Division of Medicinal Chemistry, College of Pharmacy, University of Michigan, Ann Arbor, Michigan 48109-0606, USA.
Zhao
Y
Y
Marletta
M A
MA
D002147:Calmodulin / Q000378:metabolism; D003300:Copper / Q000494:pharmacology*; D003574:Cytochrome c Group / Q000037:antagonists & inhibitors; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D009249:NADP / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D052248:Nitric Oxide Synthase Type I; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000378:metabolism*; D013482:Superoxide Dismutase / Q000378:metabolism; D015032:Zinc / Q000494:pharmacology*
D002147:Calmodulin; D003574:Cytochrome c Group; D004791:Enzyme Inhibitors; D009249:NADP; D003300:Copper; D010088:Oxidoreductases; D019001:Nitric Oxide Synthase; D052248:Nitric Oxide Synthase Type I; D013482:Superoxide Dismutase; D015032:Zinc