The capability of chymotrypsin inhibitor I from potatoes to inhibit, or be digested by, proteinases from mammalian, plant, bacterial, and fungal origins was studied. Four enzymes besides a-chymotrypsin were inhibited; Bacillus subtilis proteinase, Streptomyces griseus proteinase, carboxypeptidase B, and trypsin. The bacterial and fungal proteinases, like chymotrypsin, were stoichiometrically inhibited. However, the bacterial proteinase was not as tightly bound to inhibitor as chymotrypsin and in competition experi-

The amino acid sequences of two low molecular weight proteinase inhibitors from Russet Burbank potatoes have been determined. One of these, a chymotrypsin inhibitor, is a peptide of 52 amino acid residues, while the second inhibitor, which is specific for trypsin, contains 51 amino acid residues. These peptides are highly homologous, differing at only nine positions. At position 38, the chymotrypsin inhibitor possesses leucine and the trypsin inhibitor an arginine. This difference probably represents the P1 sites, which are consistent with the respective specificities of the two inhibitors. The inhibitors are also homologous with potato inhibitor II and with an inhibitor previously isolated from eggplants.

No abstract