 The A1 chain for cholera toxin catalyzes the transfer of ADP-ribose from Nicotinamide adenine dinucleotide(NAD) to arginine or other guanidine compounds by utilizing ADP-ribosylation factors (ARFs).In the absence of arginine or simple guanidino compounds, the toxin mediated NAD+ nucleosidase (NADase) activity proceeds using water as a nucleophile.The B subunits form a five-membered or pentameric ring, where one end of the A subunit goes into and is held.