Nitric oxide synthase activity in Fasciola hepatica: a radiometric study

Area of Science:

• Parasitology
• Biochemistry
• Enzymology

Background:

• Neuronal nitric oxide synthase (nNOS) plays a role in various physiological processes.
• Understanding nNOS activity in parasitic organisms like Fasciola hepatica is crucial for potential therapeutic targets.

Purpose of the Study:

• To quantify the activity of nNOS in adult Fasciola hepatica using a radiometric assay.
• To investigate the influence of arginase and essential co-factors on nNOS activity.
• To assess the inhibitory effects of known nNOS inhibitors and calcium chelation on enzyme activity.

Main Methods:

• Radiometric assay measuring L-[3H]citrulline production to determine nNOS activity.
• Incubation with L-valine to assess arginase inhibition effects.
• Omission of co-factors (H4B, NADPH) to evaluate their necessity.
• Application of nNOS inhibitors (L-NAME, aminoguanidine, S-methyl-L-thiocitrulline) and EGTA for calcium chelation.

Main Results:

• The study established the first radiometric measurement of nNOS activity in Fasciola hepatica.
• High arginase activity was observed, necessitating its consideration during nNOS assays.
• Significant reductions in L-[3H]citrulline formation were noted upon omission of co-factors (29%) and Ca2+ chelation (40%).
• Tested nNOS inhibitors showed varying degrees of inhibition: L-NAME (28%), aminoguanidine (15%), and S-methyl-L-thiocitrulline (14%).

Conclusions:

• Neuronal nitric oxide synthase (nNOS) activity is present in Fasciola hepatica homogenates.
• Arginase activity in F. hepatica is substantial and must be accounted for in nNOS activity measurements.
• Co-factors and calcium ions are important for optimal nNOS function in this parasite.