Abstract: Trypsin was screened in a phage displayed 15-residue peptide library for three rounds basically according to the method described by G. P. Smith. To improve the effectiveness and specificity of screening, the mothod was modified as follows. (1) During the whole screening, trypsin was kept in 0.1mol/L HEPES/20 mmol/L CaCl₂buffer(pH7.6) in order to remove most(if not all) of trypsin substrates from the peptide library.(2) Phages binding to the active site of trypsin(potential inhibitors of trypsin) were specifically eluted with trypsin inhibitor BPTI. After three rounds of screening, the potential inhibitors of trypsin were riched. Eighteen of the insert peptide sequences were determined. The result showed that the P1' residues and residues flank the scissile bonds in inhibitors are both important for the inhibitory activities. Compared with the naturally occurring inhibitors of trypsin, a 9-residue peptide DGCCRAQIT was synthesized and its inhibition constant to trypsin was determined to be 89±10 mmol/L.

Key words: Trypsin, Peptide library, Inhibitor, Serine protease