Characterization of a putative nitric oxide synthase in the neuromuscular system of the parasitic nematode, Ascaris suum

In this paper we report on the biochemical presence of nitric oxide synthas e (NOS)-like activity in Ascaris suum tissue and examine the pharmacologica l effect of NO donors on A. suum muscle strip preparation. NOS activity was determined by monitoring the formation of [H-3]citrulline from [H-3]L-argi nine and NO formation via the oxyhaemoglobin assay. Neuromuscular tissue fr om A. suum which stained positively for NADPH diaphorase, contained NOS act ivity. Neither NOS activity nor NADPH diaphorase staining was detected in i ntestinal tissue. The absence of Ca2+, NADPH and other co-factors normally required for mammalian neuronal SOS activity only partially reduced the for mation of both citrulline and NO bq A. suum neuromuscular homogenate. The r esults of the biochemical assays indicate the presence of an enzyme capable of producing NO and citrulline, but with a different profile from that of rat neuronal NOS. We also present preliminary evidence for the action of NO (NO donors) in the neuromuscular system of A. suum.