N-Chloroacetylhydrazone of oxo-GTP irreversibly inhibits the activating function of GTP-binding protein coupled with adenylate cyclase.

Guanine nucleotides are successfully used in the studies of regulatory N-proteins coupled with adenylate cyclase. In the present work N-chloroacetylhydrazones of oxo-GTP and oxo-GDP are described. After 4 hr preincubation of these nucleotides with plasma membranes from bovine brain caudate nucleus, the ability of adenylate cyclase to be activated by guanylyl-5'-methylene-diphosphonate is blocked. The degree of inhibition depends on preincubation time and increases in the presence of Mg2+. Guanylyl-5'-methylenediphosphonate protects adenylate cyclase from the action of N-chloroacetylhydrazone of oxo-GTP. These findings suggest that adenylate cyclase activation is diminished as a result of covalent modification of the Ns. N-chloroacetyl-hydrazone of oxo-GDP also causes a loss of the adenylate cyclase sensitivity to the fluoride ion and cholera toxin.