Kinetic characteristics of nitric oxide synthase from rat brain

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Abstract
The relationship between the rate of synthesis of nitric oxide (NO) and guanylate cyclase stimulation was used to characterize the kinetics of the NO synthase from rat forebrain and of some inhibitors of this enzyme. The NO synthase had an absolute requirement for L-arginine and NADPH and did not require any other cofactors. The enzyme had a Vmax of 42 pmol of NO formed.cntdot.min-1.cntdot.mg of protein-1 and a Km for L-arginine of 8.4 .mu.M. Three analogues of L-arginine, namely NG-monomethyl-L-arginine, Ng-nitro-L-arginine and N6-iminoethyl-L-ornithine inhibited the brain NO synthase. All three compounds were competitive inhibitors of the enzyme with Ki values of 0.7, 0.4 and 1.2 .mu.M respectively.