| Abstract: | Cyclic nucleotide-stimulable protein kinase (EC 1.7.1.37) has been studied in crude extracts from the central nervous system of the tobacco hornworm Manduca sexta (Lepidoptera: Sphingidae). The insect kinase was fulfhydryl-sensitive and required Mg-2+ for optimal activity. Polyacrylamide gel electrophoresis of supernatants demonstrated the presence of multiple kinases in the larval nerve cord. At low concentrations, cyclic AMP was a much more potent activator of soluble and particulate activities than was cyclic GMP. The specific activity of coluble kinase and the magnitude of its activations by cyclic AMP were greater in the adult than in the larval central nervous system. The exogenous protein substrate specificity of the insect enzyme was similar to that of rat brain kinase with the sole exception that protamine was more readily phosphorylated than histone by nerve cord kinase. It was observed that cyclic AMP lowered the Km of Manduca sexta kinase for ATP, a phenomenon which is apparently nervous tissue=specific in mammals. An effective inhibitor of cyclic AMP-dependent protein kinase was prepared from the larval central nervous system. |
