Purification, characterization, and amino acid sequence of foxtail millet trypsin inhibitor III.

One of the major trypsin inhibitors of foxtail millet, Setaria italica, was purified from a seed extract to an electrophoretically homogeneous protein by methods including chromatofocusing and affinity chromatography. This inhibitor (FMTI-III) was shown to be specific and single-headed for trypsin. The molecular weight and the amino acid composition together with the above nature were identical with those of another major trypsin inhibitor (FMTI-II) previously purified from foxtail millet grain. Sequence analysis of FMTI-III indicated that the protein contains 67 amino acid residues, the sequence of which is the same as that of FMTI-II except for the replacement of the C-terminal glutamine by glutamic acid. This single amino acid substitution had no effect on inhibitor-enzyme association.