Primary structure of Dioclea glabra trypsin inhibitor, DgTI, a Bowman-Birkinhibitor

A novel serine proteinase inhibitor, DgTI, was purified from Dioclea glabra seeds by acetone precipitation, and ion-exchange and reverse phase chromat ography. The inhibitor belongs to the Bowman-Birk family, and its primary s equence, determined by Edman degradation and mass spectrometry, of 67 amino acids is: SSGPCCDRCRCTKSEPPQCQCQDVRLNSC-HSACEACVCSHSMPGLCSCLDITHFCHEPCKSSG D- DED, Although two reactive sites were determined by susceptibility to tr ypsin (Lys(13) and His(40)), the inhibitory function was assigned only to t he first site. The inhibitor forms a 1:1 complex with trypsin, and Ki is 0. 5 x 10(-9) M. Elastase, chymotrypsin, kallikreins, factor Xa, thrombin, and plasmin were not inhibited. By its properties, DgTI is a Bowman-Birk inhib itor with structural and inhibitory properties between the class of Bowman- Birk type I (with a fully active second reactive site), and Bowman-Birk typ e II (devoid of second reactive site). (C) 1999 Academic Press.