A NEW FAMILY OF SERINE-PROTEASE INHIBITORS (BOMBYX FAMILY) AS ESTABLISHED FROM THE UNIQUE TOPOLOGICAL RELATION BETWEEN THE POSITIONS OF DISULFIDE BRIDGES AND REACTIVE-SITE

The positions of the reactive site and the disulfide bridges in fungal protease inhibitor F (FPI-F) from silkworm (Bombyx mori), which has a unique amino acid sequence and inhibitory specificity, were investiga ted, At pH 3.0, subtilisin BPN', which is one of target proteases of t his inhibitor, specifically cleaved the peptide bond of the inhibitor at Thr(29)-Val(30). The cleaved bond was regenerated by subtilisin BPN ' at pH 8.0, These results indicate that the Thr(29)-Val(30) bond of t he inhibitor is the reactive site, The locations of disulfide bridges were determined to be Cys(3)-Cys(35), Cys(14)-Cys(27), Cys(18)-Cys(55) , and Cys(37)-Cys(49). Based on the positions of the reactive site and the disulfide bridges, FPI-F is considered to be a member of a new fa mily of serine protease inhibitors, Tire propose the designation Bomby x family for the new inhibitor family of which FPI-F is a member.