THE BRAIN ADENYLATE-CYCLASE SYSTEM OF THE TOBACCO HORNWORM, MANDUCA-SEXTA - PUTATIVE CONTROL BY BIOGENIC-AMINES

The basic characteristics CNS of adenlylate cyclase from the brain of M. sexta larvae are similar to those described for CNS preparations from other insects. The properties investigated include the apparent Km for ATP in the presence of NaF, pH optimum and effects of divalent cations. Since adenylate cyclase can be activated by peptide hormones and neurotransmitters, several biogenic amines were tested on the Manduca system. The brain adenylate cyclase system is stimulated by octopamine (Ka = 1.0 .mu.M) and dopamine (Ka = 0.3 .mu.M) in the presence of guanine nucleotide, but not by serotonin. With a washed, particulate fraction, amine stimulation depends upon the addition of guanine nucleotide. Adenylate cyclase is stimulated 20- to 30-fold by NaF, the non-hydrolyzable GTP analog Gpp(NH)p, and the diterpene forskolin. Enzyme activity is dependent upon Mg2+ or Mn2+ with the latter cation being 3- to 6-fold more effective. Calmodulin activates the brain adenylate cyclase .apprx. 2-fold and this effect is Ca2+-dependent. When the enzyme is solubilized with Lubrol-PX, it retains its normal responsiveness to NaF but octopamine is no longer effective. The solubilized enzyme subjected to sucrose density centrifugation has a sedimentation coefficient of 8.9 S.