Adenylate cyclase activity from Hirudo medicinalis segmental ganglia: modulation by temperature and Mg2+ ions

The basal, serotonin- and fluoride-stimulated activities of homogenate preparations from Hirudo medicinalis segmental ganglia increase with incubation temperature, reaching a maximum at 35 degrees C. Both basal and fluoride-stimulated activities yield linear Arrhenius plots, whereas serotonin-enhanced activity shows a break at 25 degrees C. Increasing Mg2+ concentrations stimulate the adenylate cyclase both in the absence and in the presence of serotonin. The affinity of the enzymatic system for the cation is unaffected by the amine.