Potential role of SH groups in the radiosensitivity of adenylate cyclase.

The role of oxidation of SH groups in the activity of adenylate cyclase and in radiosensitivity of the enzyme was investigated. Adenylate cyclase activity was measured in purified membrane preparation of 19 day old chicken embryo brains. N-ethyl-maleimide (NEM) and lead-acetate were used as SH inhibitors. Gamma irradiation was carried out with 60-Co source. NEM inhibition of adenylate cyclase was dose dependent and 50 per cent inhibition was observed at 40-50 microM NEM. Activity of adenylate cyclase was elevated at lower concentrations of lead-acetate (10 nM-100 microM) and was inhibited at higher concentrations (above 100 microM). The presence of 40 microM NEM did not alter the shape of lead acetate saturation curve of adenylate cyclase. Gamma irradiation in the dose range of 100-800 Gy elevated the adenylate cyclase activity measured in the presence of 5 mM NaF but did not alter the basal activity. Gamma irradiation did not have significant effect on NEM saturation of adenylate cyclase, while it altered slightly the lead acetate saturation curve.