Characterization of Cyprinus carpio brain nitric oxide synthase

Nitric oxide synthase (NOS) activity is found both in soluble and in particulate fractions of the carp brain. The K-m values for arginine are 2.8 +/- 0.5 and 3.3 +/- 0.4 mu M for the soluble and particulate fractions, respectively. K-i for N-G-monomethyl-L-arginine inhibitor are 2.6 +/- 0.5 and 2.9 +/- 0.6 mu M, and activation energy for the breakdown of the substrate-enzyme complex 8120 +/- 710 and 4620 +/- 450 cal per mole. Carp enzyme shows higher affinity than rat NOS for Ca2+ and for the competitive inhibitor 7-nitroindazole.