Evidence for the Non-involvement of Nitric Oxide Synthase in Nitric Oxide Production by the Green Alga Scenedesmus obliquus

Studies conducted with NW-nitro-L-arginine (L-NNA) and NG-nitro-L-arginine-methyl ester (L-NAME), the potent inhibitors of nitric oxide synthase (NOS), did not exhibit any inhibitory effect on NO release by Scenedesmus cells grown either under illumination or in the dark supplemented with glucose. Further, these inhibitors did not interfere with the appearance of ‘light-off’ peaks, and the NO peaks also commenced following treatment with Cu, DCMU and glutarate in the presence of L-NNA and L-NAME. Complete suppression of NO production and the elimination of the most common ‘light-off’ peak were observed in algal culture grown in the medium where L-arginine was substituted for NO−3. This study therefore demonstrates that L-arginine is neither the substrate for NO production by Scenedesmus, as generally found in the case of animals and some plants, nor is the NOS involved in the nitric oxide production process.