Abstract: In the present study, an endogenous prolyl endopeptidase inhibitor (PEPI) was purified from the skeletal muscle of the marine fish blue scad (Decapterus maruadsi) by thermal precipitation, ammonium sulfate fractionation and a series of column chromatographies on DEAE-Sepharose, Sephacryl S-200 HRand HiTrap Q HP. Tricine-sodium dodecyl sulfate-polyacrylamide gel electrophoresis (Tricine-SDS-PAGE) showed that the molecular mass of PEPI was about 10 kDa. It was thermally stable and displayed tolerance to pH change. PEPI was a specific inhibitor to serine proteinase PEP and it worked in a reversible competitive manner with an inhibitory constant (Ki) of 0.34 μmol/L. A significant increase in α-helix and random coil and decrease in β-sheet were detected after formation of the PEP-PEPI complex. Quite possibly, the conformational change of PEP was the major reason for enzymatic activity inhibition.

Key words: blue scad, prolyl endopeptidase, endogenous inhibitor, inhibitory kinetics, secondary structure