NITRIC-OXIDE SYNTHASE ACTIVITY OF THE TASTE ORGAN OF THE CHANNEL CATFISH, ICTALURUS-PUNCTATUS

The constitutive nitric oxide synthase activity of the catfish taste o rgan (barbel) was characterized, using the conversion of L-[H-3]argini ne to L-[H-3]citrulline as the index of enzyme activity. The enzyme wa s dependent on Ca2+ (but not calmodulin) and NADPH (but not FAD). Acti vity was moderately enhanced by tetrahydrobiopterin. Kinetic parameter s were K-m = 22 mu M and V-max = 25 pmol/min/mg. The enzyme was inhibi ted by N-G-monomethyl-L-arginine (half-maximally at 3 mu M) and N-G-ni tro-L-arginine (half-maximally at 50 mu M), and also by sodium nitropr usside and superoxide dismutase. In the presence of millimolar levels of the taste stimulus L-alanine, nitric oxide synthase activity was in creased by up to 3-fold, with activation of the enzyme being reversed by N-G-monomethyl-L-arginine. There was no activation of guanylyl cycl ase by L-alanine. These data indicate that a constitutive nitric oxide synthase activity is present in the catfish taste organ and that, the refore, nitric oxide may have a role in the biochemical mechanisms und erlying taste perception.