The role of adenine and guanine nucleotides in the activity and response of adenylate cyclase systems to hormones: evidence for multi site transition states

Abstract

Evidence is presented that the glucagon sensitive adenylate cyclase system in rat hepatic plasma membranes has the characteristics of an allosteric regulatory enzyme. Based primarily on kinetic considerations, the studies indicate that the activity of the enzyme is controlled by hormone, guanine nucleotides, and by the protonated species of substrate (HATP 3-), each ligand interacting selectively with sites termed receptor or discriminator, nucleotide regulatory site, and active site, respectively. Evidence is also presented that hormonal activation of adenylate cyclase systems in eucaryotic cells has characteristics in common with the glucagon sensitive hepatic system.