Interaction of Vibrio cholerae Toxin with Sarcoma 180 Cell Membranes

Abstract

Three discrete phases are discernible in the activation, by Vibrio cholerae toxin, of adenylate cyclase in fragments of sarcoma 180 cell membranes. In the first, or preparatory, phase the toxin must be exposed to dithiothreitol or nicotinamide adenine dinucleotide (NAD) in the absence of the membranes. In the second phase, the prepared toxin is dissociated to yield a macromolecular cyclaseactivating factor (MCAF) in the presence of the membranes. In the third phase, membrane basal adenylate cyclase is activated by MCAF in the presence of NAD. The integrity of the catecholamine or β-receptor associatedwith sarcoma adenylate cyclase is irrelevant in the activation of cyclase by MCAF. This activation proceeds undiminished even if the β-receptor is desensitized or blocked by propranolol.