Characterization of an octopamine-sensitive adenylate cyclase from insect brain (Mamestra configurata Wlk.)

An adenylate cyclase present in the brain of the moth Mamestra configurata Wlk. that is stimulated selectively by low (micromolar) concentrations of octopamine has been characterized with respect to several properties. The optimum pH, optimum ATP:Mg2+ ratio, the concentration of ATP required for half-maximal and maximal reaction velocity, metal ion specificity, effect of NaF, and effects of GTP and 5'-guanylylimidodiphosphate were in general similar to those of catecholamine-sensitive adenylate cyclases from various regions of mammalian brain. However, ethylene glycol bis-(beta-aminoethyl ether)-N,N-tetraacetic acid (EGTA), a calcium chelator, stimulated both basal and octopamine-sensitive enzyme activity in the insect brain, whereas in mammalian brain EGTA is usually observed to inhibit basal activity but not catecholamine-stimulated activity. Adenylate cyclase activity of the 47,000 g particulate fraction of the insect brain was almost undetectable in the absence of added GTP. Addition of saturating concentrations (100 micrometer) of GTP to the particles restored about 30% of the basal and octopamine-sensitive enzyme activity present in the homogenate. Addition of 100,000 g supernatant to the particles doubled both basal and octopamine-sensitive enzyme activity in the presence of saturating concentrations of GTP, indicating that in addition to GTP, a cytosolic factor(s) is necessary for enhanced adenylate cyclase activity.