ADP-ribosyltransferase C3 from Clostridium botulinum ribosylates rho in eukaryotes in the presence of NAD. The ADP-ribosylating exoenzyme forms a single major 25 kDA (approx.) band with SDS electrophoresis. The enzyme labels 21-24 kDa proteins in tissues such as the human platelet membranes.', 'Ribosylates rho in eukaryotes in the presence of NAD.