SYNTHESIS OF POLY(ETHYLENE GLYCOL) DERIVATIVES WITH DIFFERENT BRANCHINGS AND THEIR USE FOR PROTEIN MODIFICATION

Monomethoxy linear poly(ethylene glycol) (PEG) with a terminal hydroxy group was coupled to monobromoacetic acid, protocatechnic acid and ga llic acid to synthesize one branched (PEG1), two branched (PEG2) and t hree branched PEG derivatives (PEG3) each having only one carboxyl gro up in a molecule. The PEG derivatives were chemically fixed to trypsin through amidation with its amino groups using the PEG carboxyl group. The PEG-modified trypsins with different degrees of modification were subjected to three enzymatic reactions. When casein hydrolysis and tr ypsin autolysis were performed using the PEG-modified trypsins, both o f the enzymatic reactions were strongly suppressed with the PEG modifi cation. On the other hand, inhibition of trypsin activity by trypsin i nhibitor was scarcely affected by the PEG modification, whereas trypsi n digestion by pepsin was greatly protected by the PEG modification in the order of PEG3 > PEG2 > PEG1. All these results could be consisten tly explained in terms of steric hindrance brought about by fixation o f the PEG chains on the trypsin molecule.