Human platelet nitric oxide synthase activity: an optimized method

We investigated the kinetic analysis of human platelet Nitric Oxide Synthase (NOS) activity by the rate of conversion of [3H] arginine to [3H]-citrulline in unstimulated fresh platelets. NOS activity was present in the membrane fraction and cytosol, and was Ca²+ - and calmodulin dependent which is a characteristic of endothelial NOS. NOS activity was also dependent of NADPH since the omission of this cofactor induced an important decrease (85,2 por cento) in the enzyme activity. The kinetic varied with protein and arginine concentration but optimum concentrations were found up to 60 minutes, and up to 80 µg of protein at 120 nM of argine and 0.5 µCi of3H-arginine...