An ADP-ribosyltransferase from bovine erythrocytes apparently specific for cysteine residues

An NAD+:cysteine glycohydrolase purified from bovine erythrocytes had a specific activity of 1900 (nmol nicotinamide released).min-1.mg-1, a K(m) for cysteine of 4.0 mM, and an M, of 45,000. The enzyme also catalysed the dose-dependent ADP-ribosylation of several bovine erythrocyte proteins, including a doublet of high M(r) and proteins of M(r) 60,000, 55,000, and 29,000. ADP-ribosylation of the M(r) 55,000 protein was blocked by pre-treatment of the erythrocyte membranes with N-ethylmaleimide, and ADP-ribose was released by treatment with mercuric ions, but not with hydroxylamine. The enzyme therefore appears to be a cysteine-specific ADP-ribosyltransferase.