Purification of a novel serine proteinase inhibitor from the skeletal muscle of white croaker (Argyrosomus argentatus)

A novel serine proteinase inhibitor has been purified to homogeneity from t he skeletal muscle of white croaker (Argyrosomus argentatus). The purificat ion was carried out by ammonium sulfate fractionation, DEAE-Sephacel, heati ng treatment followed by column chromatographies on SP-Sepharose, Sephadex G-150 and gel-filtration high performance liquid chromatography, The molecu lar mass of the inhibitor was 55 kDa as estimated by SDS-PAGE and gel filtr ation. It specifically inhibited a myofibril-bound serine proteinase ((MBSP ) isolated from the skeletal muscle of lizard fish (Saurida wanieso). No in hibition, however, was detected toward other serine proteinases such as bov ine trypsin, bovine chymotrypsin and a myofibril-bound serine proteinase fr om carp (Cyprinus carpio) muscle. Interestingly, the sequences of tryptic d igested peptide fragments of MBSPI revealed high identity to that of porcin e phosphoglucose isomerase (PGI) (76%) and other PGIs. Furthermore, purifie d MBSPI exhibits PGI activity, suggesting the inhibitor is a protein closel y related to PGI. When rabbit muscle PGI was investigated, it also specific ally suppressed the activity of MBSP, It thus strongly suggests that MBSPI is actually PGI and conversely, PGI is a specific inhibitor toward myofibri l-bound serine proteinase(s). (C) 2000 Academic Press.