ADP-ribosyltransferase activity of mono- and multi-(ADP-ribosylated) choleragen

Choleragen (cholera toxin) catalyzed the NAD-dependent auto-ADP-ribosyltation of its A1 peptide. The number of ADP-ribose moieties incorporated into ech A1 peptide was dependent on incubation conditions and time as well as toxin concentration. There was no evidence for the formation of poly(ADP-ribosylated) toxin. The formation of mono- and multi-(ADP-ribosylated) A1 peptides was prevented by the addition of arginine, an alternative ADP-ribose acceptor. Triton X-100 polyacrylamide gel electrophoresis separated the A1 peptide of choleragen from the B complex and multi-(ADP-ribosylated) A1 peptides from unmodified A1. The A1 peptides ADP-ribosylated in the presence of [32P]NAD contained approximately 1, 2, or 3 ADP-ribose molecules/23,500-dalton units; under the conditions used for electrophoresis, the mobilities of the A1 peptides were enhanced by incorporation of ADP-ribose. The mono- and multi-(ADP-ribosylated) A1 peptides catalyzed the NAD-dependent ADP-ribosylation of arginine methyl ester. The turnover numbers of the mono- and multi-(ADP-ribosylated) A1 peptides were consistently 30 to 50% higher than that of the A1 peptide from native toxin.