ISOLATION AND CHARACTERIZATION OF A NEW INHIBITOR OF TRYPSIN AND CHYMOTRYPSIN FROM POTATO-TUBERS

A proteinaceous inhibitor of trypsin and chymotrypsin has been isolate d from potato tuber (Solanum tuberosum L.). The isolation procedure in cludes precipitation with ammonium sulfate, gel chromatography on Seph adex G-75, and ion-exchange chromatography on DEAE-cellulose. The inhi bitor molecule consists of one polypeptide chain with molecular mass o f 17 +/- 1 kD and pI = 6.8. The inhibitor interacts with trypsin or ch ymotrypsin in 1:1 molar ratio; the enzyme-inhibitor complexes undergo substrate-dependent dissociation. The inhibitor does not suppress the activity of subtilisin or pancreatic elastase. Formation of a ''triple '' complex containing one trypsin molecule and one chymotrypsin molecu le indicates that the inhibitor has two independent active centers for these enzymes.