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

Z.A.  BASCAL  a1, J.M.  CUNNINGHAM  a2 p1, L.  HOLDEN-DYE  a1, M.  O'SHEA  a2 and R.J.  WALKER  a1 c1
a1 Division of Cell Sciences, School of Biological Sciences, University of Southampton SO16 7PX
a2 Sussex Centre for Neuroscience, School of Biological Sciences, University of Sussex, Brighton BN1 9QG


In this paper we report on the biochemical presence of nitric oxide synthase (NOS)-like activity in Ascaris suum tissue and examine the pharmacological effect of NO donors on A. suum muscle strip preparation. NOS activity was determined by monitoring the formation of [3H]citrulline from [3H]L-arginine and NO formation via the oxyhaemoglobin assay. Neuromuscular tissue from A. suum which stained positively for NADPH diaphorase, contained NOS activity. Neither NOS activity nor NADPH diaphorase staining was detected in intestinal tissue. The absence of Ca2+, NADPH and other co-factors normally required for mammalian neuronal NOS activity only partially reduced the formation of both citrulline and NO by A. suum neuromuscular homogenate. The results 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.

(Received April 22 2000)
(Revised August 14 2000)
(Accepted August 21 2000)

Key Words: Ascaris suum; nematode; invertebrate; nitric oxide synthase.

c1 Corresponding author: Division of Cell Sciences, School of Biological Sciences, University of Southampton, Bassett Crescent East, Southampton SO16 7PX, UK. Tel: +02380594343. Fax: +02380594319. E-mail:
p1 Present address: School of Pharmacy and Biomolecular Sciences, University of Brighton, Brighton BN2 49J.