The purpose of this project is to gain some understanding of the chemistry of the early events in hormone action. As many hormones do not enter their target cell, the plasma membrane is the site at which the hormone is bound and at which the cellular response is initiated. The response seems to be mediated in many cases by cyclic 3' 5' adenosine monophosphate cyclic AMP which is formed as a result of hormonal stimulation of membrane-bound adenyl cyclase. One hormone-target cell system in which adenyl cyclase activation plays an important part is that of vasopressin in the renal medulla. We propose to isolate and examine both the hormone receptor and the hormone sensitive adenylate cyclase from the bovine renal medulla. The aim is to solubilize both components and we have begun with the enzyme. It has been solubilized and it is possible to study its size and its interaction with the detergents used to remove it from the membrane. We are now devising methods to purify the enzyme in the quantities necessary for precise chemical and physical studies.