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Porasuphatana S, Tsai P, Pou S, Rosen GM: Involvement of the perferryl complex of nitric oxide synthase in the catalysis of secondary free radical formation. Biochim Biophys Acta. 2001 Apr 3;1526(1):95-104.
Neuronal nitric oxide synthase (NOS I) has been shown to generate nitric oxide (NO*) and superoxide (O (2)* during enzymatic cycling, and the ratio of each free radical is dependent upon the concentration of L-arginine. Using spin trapping and electron paramagnetic resonance spectroscopy, we detected alpha-hydroxyethyl radical (CH (3)*CHOH), produced during the NOS I metabolism of ethanol (EtOH). The generation of CH (3)*CHOH by NOS I was found to be Ca (2+)/calmodulin dependent. Superoxide dismutase prevented CH (3)*CHOH formation in the absence of L-arginine. However, in the presence of L-arginine, the production of CH (3)*CHOH was independent of O (2)* but dependent upon the concentration of L-arginine. Formation of CH (3)*CHOH was inhibited by substituting D-arginine for L-arginine, or inclusion of the NOS inhibitors N (G)-nitro-L-arginine methyl ester, N (G)-monomethyl-L-arginine and the heme blocker, sodium cyanide. The addition of potassium hydrogen persulfate to NOS I, generating the perferryl complex (NOS-[Fe (5+)=O](3+)) in the absence of oxygen and Ca (2+)/calmodulin, and EtOH resulted in the formation of CH (3)*CHOH. NOS I was found to produce the corresponding alpha-hydroxyalkyl radical from 1-propanol and 2-propanol, but not from 2-methyl-2-propanol. Data demonstrated that the perferryl complex of NOS I in the presence of L-arginine was responsible for catalyses of these secondary reactions. |
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