ADP‐Ribosylation by Cholera Toxin of Membranes Derived from Brain Modifies the Interaction of Adenylate Cyclase with Guanine Nucleotides and NaF

Abstract

We have developed a method of ADP-ribosylate the stimulatory guanine nucleotide-binding protein of adenylate cyclase (Gs) in brain membranes by using cholera toxin. In particular, we used isonicotinic acid hydrazide and 3-methylpyridine adenine dinucleotide to inhibit the potent NAD-glycohydrolase activity of brain membranes, and we used the detergent Triton X-100 (at 0.1%) to improve the accessibility to the toxin and guanine nucleotides used for supporting the ADP-ribosylation. This method reveals that Gs is a very abundant protein in membranes derived from calf brain (.apprx. 30 pmol/mg of protein). In brain, Gs exists in large excess over the previously reported amount of the adenylate cyclase catalytic subunit. The modification of Gs with an ADP-ribosyl residue (a) elicits a four- to fivefold activation of adenylate cyclase by GTP, (b) increases the stabilization of adenylate cyclase by GTP, and (c) reduces adenylate cyclase activation by fluoride but does not change basal activity, activation by guanosine 5''-(.beta.,.gamma.-imido)triphosphate, or the sensitivity of adenylate cyclase to heat-induced denaturation. A correlation between ADP-ribosylation and the alterations in the activation of adeylate cyclase by guanine nucleotides and by fluoride is presented.