ORIGIN OF THE ENZYMATICALLY ACTIVE-A1 FRAGMENT OF CHOLERA TOXIN

Cholera toxin consists of five B subunits that are responsible for binding to receptors and a single A subunit that catalyzes the intracellular (or in vitro) adenosine diphosphate (ADP)-ribosyla-tion and activation of adenylate cyclase [1, 2]. Sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis showed that the apparent molecular weight of subunit A is about 26, 00029, 000. Hitherto, the A subunit has always been found to consist of two polypeptide chains that are linked by a single disulfide bond and are usually referred to as Ax (mol wt, -21, 000-24, 000; enzymatically active) and A2 (mol wt, -5, 000-7, 000; enzymatically inactive) [3-6]. Both subunits have been partially sequenced [6-8]. © 1979 by The University of Chicago.