Surface modification of proteins. Activation of monomethoxy-polyethylene glycols by phenylchloroformates and modification of ribonuclease and superoxide dismutase.

A single-step method of activation of monomethoxypolyethylene glycols suitable for its binding to polypeptides and proteins is proposed. Based on the reaction with 2,4,5-trichlorophenylchloroformate or p-nitrophenylchloroformate, it gives reactive PEG-phenylcarbonate derivatives. The PEG intermediate is stable on storage, the activating group is easily quantified,and the reaction with amino acid and proteins proceeds rapidly at pH near neutrality. The PEG derivatization of enzymes with this procedure is less inactivating than those previously reported. Ribonuclease and superoxide dismutase were modified and the effect of (a) bound polymer on clearance time in rats, (b) antibody recognition, and (c) on the enzymatic activity toward low and high molecular weight substrates were studied.