PARTIAL CHARACTERIZATION OF TRYPSIN-INHIBITORS AND N-TERMINAL SEQUENCES OF 5 TRYPSIN ISOINHIBITORS OF GREAT NORTHERN BEANS (PHASEOLUS-VULGARIS)

A purified pool of Great Northern (GN) bean trypsin inhibitors (TIs), subjected to SDS-PAGE containing 7 M urea, produced four broad bands when stained for protein. Reduction and S-carboxymethylation of the purified GN bean TIs followed by SDS-PAGE resulted in the production of several sharp bands with estimated molecular weights ranging from approximately 8000 to 17 000. Plasma desorption mass spectrometry of the collective pool of purified GN bean TIs resulted in two peaks of molecular weight 8406 and 8957. One isolated GN bean TI, subjected to amino acid compositional analysis, contained neither Val nor Met, was low in Tyr, Leu, Phe, and Arg, and contained high amounts of Cys, Asp, Ser, and Glu. The pI values of seven of the GN bean TIs were estimated to be pH 5.14, 4.97, 4.88, 4.76, 4.69, 4.64, and 4.56. N-Terminal sequence analysis of five GN bean TIs revealed that four of the TIs contained Ser at the N terminus, while a fifth contained Lys at position 1 and Ser at position 2. Three of the TIs exhibited a high degree of sequence homology among themselves and with other plant source TIs, while two of the TIs exhibited little sequence homology among themselves or with the other GN bean TIs.