SORGHUM PROTEINASE INHIBITORS:

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Abstract
An investigation has been carried out on the proteinase inhibitors of grain sorghum (Sorghum bicolor (L.) Moench). One of the inhibitors has been isolated in a pure form and characterized. The proteinase inhibitor was extracted from the acetone‐defatted sorghum meal and purified by selective thermal denaturation, ammonium sulfate fractionation, Sephadex gel filtration and DEAE‐cellulose chromatography (DEAE‐preparation II). This preparation was demonstrated to be a mixture of three inhibitor components by polyacrylamide disc gel electrophoresis. Further resolution of this mixture into Inhibitors I to III was achieved by QAE‐Sephadex chromatography. Sorghum Inhibitor III was homogeneous by the criteria of disc gel electrophoresis and has been more fully characterized. A molecular weight of 25,000 was obtained for Inhibitor III by gel filtration and was in agreement with the value calculated from the amino acid composition of the inhibitor. The N‐terminal amino acid residue of Inhibitor III, a single chain protein, was isoleucine. Sorghum proteinase inhibitors inhibit specifically the serine proteinases and are inactive towards the other classes of proteinases. Inhibitor III is primarily a chymotrypsin inhibitor, whereas Inhibitors I and II inhibit both trypsin and chymotrypsin.