Mn 2+-uncoupling of the catecholamine-sensitive adenylate cyclase system of rat reticulocytes parallel effects on cholera toxin-catalyzed ADP-ribosylation of the system

Abstract

High concentrations of Mn 2+ interfere with functional interactions between the GTP-binding regulatory protein (G) and the catalytic moiety (C) of adenylate cyclase without perturbing interactions between receptor (R) and component G in the reticulocyte membranes. The ability of chlora toxin of to ADP-ribosyle component G and to enhanced GTP-stimulated adenylate cyclase activity also appears to be correlated with the efficacy of the communication of component G with the adenylate cyclase system. Thus, increasing the concentration of Mn 2+ in rat reticulocyte membrane during in vitro incubations causes a parallel loss of Gpp(NH)p-stimulated adenylate cyclase activity, cholera toxin-catalyzed [ 32P]ADP-ribosylation of the 40 000 M r submit of compoment G and cholera toxin-catalzed enhancement of GTP-sensitive adenylate cyclase activity. Removal of Mn 2+ by washing the membranes completely restores the sensitivity of adenylate cyclase to al effectors, including cholera toxin. The data suggest that exposure of membranes to Mn 2+ provides a useful tool for reversibly uncoupling catecholamine-sensitive adenylate cyclase systems. The data also suggest that the extent of choleratoxin-catalzed ADP-ribosylation of membrane substrates, i.e., the G component may rely on functional communication amongs the various components of the adenylate cyclase system. A corollary of the latter is the amount of [ 32P]ADP-ribose-product detected in a membrane may reflect both the quantity and coupling efficiency of component G.