Adenylate and guanylate cyclase activities in isolated guinea pig epidermal cells at various stages of differentiation.

The enzymatic properties of adenylate and guanylate cyclases were examined in sonicates of trypsinized guinea pig epidermal cells as enzyme source. Adenylate cyclase was found to be membrane-bound, while guanylate cyclase activity was detected in both membrane and cytosolic fractions. The maximal activities of the enzymes were obtained in the presence of Mn++ in the pH range 7.8-8.8. The apparent Km values of adenylate cyclase for Mn++- and Mg++-ATP were 20.5 and 38.6 microM, respectively, while the value of guanylate cyclase for Mn++-GTP was 500 microM. Examinations of cells separated by velocity sedimentation at unit gravity revealed that the basal activity of adenylate and guanylate cyclases was maximal in the germinative cells, falling gradually to the low level as cells differentiated. We assume that in the epidermis, the control and coordination of proliferation require higher concentrations of adenylate and guanylate cyclases as compared with events occurring during terminal differentiation.