Nitric oxide synthase activity in molluscan hemocytes.
The hemocytes of the freshwater snail Viviparus ater have nitric oxide synthase (NOS) activity, as demonstrated by [3H]citrulline and nitrite + nitrate formation. The enzyme is NADPH dependent and is competitively inhibited by the mammalian NOS inhibitor NG-monomethyl-L-arginine (Ki = 4.7 microM). The Km for L-arginine is 2.5 microM. 70% of the total activity is observed at very low free Ca2+ concentration (3 nM). LPS treatment increased total NOS activity 2.4 fold. The activity is partly present in the non-soluble fraction of hemocytes (24% and 8% in non-stimulated and LPS-stimulated snails, respectively). An antiserum to the C-terminal synthetic pentadecapeptide of the rat cerebellar NOS inhibited the enzyme activity in a concentration-dependent manner. This is the first biochemical demonstration of the existence of NOS activity in molluscan hemocytes, the cells responsible for defence mechanisms.
Conte
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Department of Animal Biology, University of Modena, Italy.
Ottaviani
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D000594:Amino Acid Oxidoreductases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000818:Animals; D000906:Antibodies / Q000494:pharmacology; D001120:Arginine / Q000031:analogs & derivatives / Q000494:pharmacology; D002956:Citrulline / Q000378:metabolism; D006434:Hemocytes / Q000201:enzymology*; D007700:Kinetics; D009566:Nitrates / Q000032:analysis; D019001:Nitric Oxide Synthase; D009573:Nitrites / Q000032:analysis; D011817:Rabbits / Q000276:immunology; D012908:Snails / Q000201:enzymology*; D019323:omega-N-Methylarginine
D000906:Antibodies; D009566:Nitrates; D009573:Nitrites; D019323:omega-N-Methylarginine; D002956:Citrulline; D001120:Arginine; D019001:Nitric Oxide Synthase; D000594:Amino Acid Oxidoreductases