Comparative physico-chemical studies on purified trypsin inhibitors from the endosperm of barley, rye, and wheat.

The dominant trypsin inhibitors of the endosperm of barley, rye and wheat were investigated in a series of comparative studies. The barley and rye inhibitors showed a reaction of partial immunochemical identity, whereas no immunological cross-reactions between the wheat inhibitor and the inhibitors from barley and rye were detected. The molecular weight of the barley inhibitor is about 14,500, and of the rye and wheat inhibitors about 12,000. The three inhibitors had very similar amino acid compositions, but the wheat inhibitor seemed to contain nine disulfide bridges whereas the barley and rye inhibitor contain five and four, respectively. This may explain the higher stability of the wheat inhibitor towards proteolytic inactivation by pepsin and chymotrypsin. All three inhibitors were very stable to temperatures at 100 degrees C. The barley inhibitor was much less active against porcine trypsin, and especially human trypsin, than against bovine trypsin, whereas the inhibition by the rye and wheat inhibitor was less dependent on the origin of the enzyme.