Biochemical Characterization and Cytochemical Localization of a Catecholamine-Sensitive Adenylate Cyclase in Isolated Capillary Endothelium

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Abstract
Capillaries were isolated from epididymal fat, and a catecholamine-sensitive adenylate cyclase found in these capillaries was characterized. The effect of various hormones on the accumulation of adenosine 3′:5′-cyclic monophosphate in capillary endothelial cells was determined and the cyclase was found to exhibit mixed alpha and beta characteristics. Cyclase was cytochemically localized in these endothelial cells with 5′-adenylyl-imidodiphosphate as a specific cyclase substrate and alloxan as a specific cyclase inhibitor. Lead imidodiphosphate was precipitated at or near the site of cyclase activity upon hydrolysis of 5′-adenylyl-imidodiphosphate by cyclase. This reaction product was observed primarily on the luminal surface of intact capillaries, in micropinocytic invaginations, in free vesicles within the cytoplasm, and in the intracellular junctions.