The invention relates to a
polyethylene glycol (PEG) modification method. The method is capable of realizing selective modification of carbon terminal carboxyl groups of proteins and polypeptides, and each
protein molecule and polypeptide molecule is connected with one PEG molecule. According to the method,
staphylokinase is used as a
model protein. The
polyethylene glycol (PEG) modification method comprises following main steps: (1) under slightly acidic conditions (pH 5.0), carboxyl groups of
staphylokinase and amino groups of
cystamine are connected; and (2) reduction of disulfide bonds of
cystamine is realized using a
reducing agent, and generated sulfhydryl groups are reacted with methoxy
polyethylene glycol-maleinimide (mPEG-Mal). pKa value of the carbon terminal carboxyl groups of
staphylokinase is 2.1 to 2.4, pKa value of
side chain carboxyl groups of
aspartic acid is 3.7 to 4.0, and pKa value of
side chain carboxyl groups of
glutamic acid is 4.2 to 4.5, so that under the conditions with a pH value of 5.0, PEG is capable of realizing selective modification of the carbon terminal carboxyl groups of staphylokinase. The method is mainly used for PEG selective modification of the carbon terminal carboxyl groups of the proteins and the polypeptides; a novel
PEG modification method is provided; and an
advantage of the method is that uniformity of modification sites of the
PEG modification product is excellent.