Cytochemical localization of adenylate cyclase.

This study examined 1) the effect of lead and fixation on adenylate cyclase activity, 2) the effect of lead on App(NH)p, and 3) the specificity of App(NH)p as a substrate for adenylate cyclase under the conditions of the cytochemical assay. The results indicated that: 1) fixation that provides adequate structural preservation inhibits enzyme activity to varying degrees depending on the tissue, fixative, length and temperature of fixation; 2) millimolar concentrations of lead do not negatively affect the adenylate cyclase activity of several different tissues (especially if 10 mM NaF is present); 3) lead does not cause the nonenzymatic hydrolysis of App(NH)p; 4) the App(NH)p obtained from the supplier is contaminated and should be purified before use, since lead can interact with the contaminants and this may be a source of error in the assay; and 5) adenylate cyclase appears to be the major enzyme that cleaves App(NH)p under cytochemical conditions.