ACYLATION OF AMINO FUNCTIONS OF PROTEINS WITH MONOMETHOXYPOLY(ETHYLENE GLYCOL)-N-SUCCINIMIDE CARBONATE

Monomethoxypoly(ethylene glycol)-N-succinimide carbonate (SC-PEG) was used to prepare PEG-lysozyme, PEG-papaya proteinase III, PEG-catalase, and PEG-lactoperoxidase conjugates. SC-PEG produced extensively modif ied enzymes under mild conditions (pH 7.0; 25 degrees C) within a coup le of hours. PEG-enzyme conjugates showed equal or even greater specif ic activity provided that low-molecular-weight substrates were used to evaluate the biological activities. However, papaya proteinase III an d lysozyme lost their proteolytic and bacteriolytic activities, respec tively, on conjugation with PEG. This was most probably because of ste ric factors, since no drastic conformational changes could be detected after conjugation of these enzymes with PEG chains. Unlike these enzy mes, the secondary structures of the two hemoproteins were somewhat af fected by the covalent attachment of PEG chains as shown by FTIR exper iments. These results confirmed the potential usefulness of SC-PEG, fo r which a novel route of synthesis making use of N,N'-disuccinimidyl c arbonate was described.