Isolation and properties of trypsin and chymotrypsin inhibitors from barley grits after storage

Abstract

AbstractThe occurrence of antiproteolytic activity in albumins of barley grits has been shown. As a result of storage lasting 6 months at a temperature of −10 °C the freeze‐dried albumin of barley grits lost its antiproteolytic activity and a proteolytic activity appeared. The antiproteolytic activity was partially regained after dissociation of the enzyme–inhibitor complex which had formed. From the reactivated freeze‐dried albumins of stored barley grits two thermolabile protease inhibitors were isolated and partially purified. The first trypsin–chymotrypsin inhibitor B7.1 inhibits, at a concentration of 2.5 μg, 1 μg of crystalline trypsin and 1.9 μg of this inhibitor inhibits 1 μg of crystalline alpha‐chymotrypsin. Lower activity was demonstrated for the second inhibitor of chymotrypsin B7.4; 4.8 μg of this inhibitor is needed to inhibit the activity of 1 μg of crystalline alpha‐chymotrypsin. The occurrence of both inhibitors has been confirmed by means of starchgel electrophoresis. Their specific activity was small in comparison with that of some commercial crystalline preparations of inhibitors. The capacity to inhibit native proteases shows their important physiological function, based mainly on the control of proteolytic activity of endogenous enzymes. However it seems unlikely that they could have a negative influence on the nutritive value of proteins in barley grains or grits.