FURTHER CHARACTERIZATION OF PROTEASE INHIBITORS FROM PIGEON PEA (CAJANUS-CAJAN (L) MILLSP) SEEDS

Cajanus trypsin inhibitor (CTI) and Cajanus trypsin-chymotrypsin inhib itor (CTCI) previously purified from cv TAT-10 were further characteri sed. The modification of the inhibitors revealed the presence of lysin e at the trypsin reactive site in both CTI and CTCI. Modification of t yrosine at the reactive site of CTCI did not abolish chymotrypsin inhi bition suggesting the presence of leucine or phenylalanine as reported in other chymotrypsin inhibitors. CTCI did not contain tryptophan. Di ssociation constants for the inhibitors with bovine trypsin were in th e region of 0.69 nmol (CTCI) and 0.029 nmol (CTI). Although the protea se inhibitors lost their inhibitory activity on exposure to 2-mercapto ethanol they remained attached to the enzyme. The inhibitors were not very effective against the protease from Helicoverpa armigera which is a serious field pest of Cajanus. Dissociation constants for the inhib itors with the larval enzyme were in the region of 100 nmol.