STRUCTURE-FUNCTION RELATIONSHIPS OF SOYBEAN DOUBLE-HEADED PROTEINASE INHIBITORS

Abstract

This chapter discusses the structure–function relationships of soybean double-headed proteinase inhibitors. Many of the natural proteinase inhibitors inhibit more than one proteinase at the same time, and are called multi-headed inhibitors. The most extensively investigated multi-headed inhibitors are the double-headed inhibitors of legume origin, which can bind two proteinases at their dual and independent reactive sites. The soybeans used for the purification of inhibitors are the Sode-furi variety, cropped in 1973. Soybean meals were extracted with 60% ethanol at room temperature and the inhibitor fraction was precipitated by adding a double volume of cold acetone. The sticky precipitates were collected, dissolved in water, and dialyzed against water. Fraction A was found to be BBI by its chromatographic behavior, inhibitory pattern, and the amino acid composition of the purified materials. Fraction B was purified on a DE-32 column using ammonium acetate buffer system according to Frattali. Fraction C was first purified on a DEAE-cellulose column. Two major fractions, C-I and C-II, were obtained. C-II was further purified by SP-Sephadex C-25 chromatography and finally by DEAE-cellulose chromatography.