Uncoupling of gonadotropin-sensitive adenylate cyclase by N,N'-dicyclohexylcarbodiimide. Evidence for modification of two sites

Treatment of purified rat ovarian plasma membranes with N,N'-dicyclohexylcarbodiimide (DCC) abolishes the subsequent response of Adenylate Cyclase [EC 4.6.1.1, ATP pyrophosphate lyase (cyclizing)] to lutropin (LH) and follitropin (FSH) but not to NaF. Such treatment also inhibits binding to these membranes of iodinated [125I] human chorionic gonadotropin (125I-hCG). Preincubation for 30 min at room temperature with 70 microM DCC reduces the response of Adenylate Cyclase to LH by 50% whereas 4 times higher concentration is required to reduce 125I-hCG binding to the same extent. At 0.5 mM, DCC reduces both activities by 50% within 8-10 min. Preincubation of the membranes with hCG prior to treatment with DCC protects the hormone-binding site of the receptor but not the ability of the Enzyme to respond to LH. Thus the Enzyme becomes functionally uncoupled. It is suggested that at least two distinct sites in the Enzyme system are affected by DCC. Both sites are located proximal to the regulatory step that involves GTP-binding protein. One site seems to be associated with the receptor and the second is located distal to receptor-hormone complex formation.