Biochemical Characterization and Histochemical Localization of Nitric Oxide Synthase in the Nervous System of the Snail, Helix pomatia

Nitric oxide synthase (NOS) in the snail Helix pomatia was characterized by biochemical and molecular biological techniques and localized by histochemical methods. Central ganglia contained particulate paraformaldehyde-sensitive and cytosolic paraformaldehyde-insensitive NADPH-diaphorase. The cytosolic NADPH-diaphorase activity coeluted with NOS activity. The activity of NOS was dependent on Ca2+ and NADPH and was inhibited by N(G)-nitro-L-arginine (L-NNA). Proteins purified by 2',5'-ADP affinity chromatography were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and migrated at 150, 60, 40, and 30 kDa. An antibody to mammalian NOS exclusively labeled the 60-kDa protein. Characterization of the cDNA of the corresponding 60-kDa NOS-immunoreactive protein revealed no sequence homology with any known NOS isoform. The recombinant protein exhibited Ca2+- and NADPH-dependent NOS activity, which was partially inhibited by EGTA and L-NNA. Histochemistry showed NADPH-diaphorase activity in discrete regions of the central and peripheral nervous system. About 60% of the NADPH-diaphorase-positive neurons colocalize with immunoreactive material detected by antibodies to mammalian NOS. Comparison of organs showed the highest NADPH-diaphorase activity in the nervous system, whereas moderate activity was present in muscle tissue, digestive tract, and gonads. Our study suggests the presence of NOS and a putative NOS-associated/regulating protein in mollusk nervous tissue.