THE AMINO-ACID-SEQUENCE AND REACTIVE-SITE OF A SINGLE-HEADED TRYPSIN-INHIBITOR FROM WHEAT ENDOSPERM

The sequence of a trypsin inhibitor, isolated from wheat endosperm, is reported. The primary structure dris obtained by automatic sequence a nalysis of the S-alkylated protein and of purified peptides derived fr om chemical cleavage by cyanogen bromide and digestion with Staphyloco ccus aureus V8 protease. This protein, named wheat trypsin inhibitor ( WTI), which is comprised of a total of 71 amino acid residues, has 12 cysteines, all involved in disulfide bridges. The primary site of inte raction (reactive site) with bovine trypsin has been identified as the dipeptide arginyl-methionyl at positions 19 and 20. WTI has a high de gree of sequence identity with a number of serine proteinase inhibitor s isolated from both cereal and leguminous plants. On the basis of the findings presented, this protein has been classified as a single-head ed trypsin inhibitor of Bowman-Birk type.