Polyacrylamide-gel electrophoresis of soybean whey proteins and trypsin inhibitors.

Polyacrylamide·.g~1 electrophoresis with glycine buffer (pH 9.2) containing 8 M urca separated soybean whey proteins into at least 24 bands. In contrast, ultracentrifugation indicated only 2 fractions; moving-boundary electrophoresis, 8-9 components; and column chromatography, 13 or more proteins. A prominent, fast-moving band in the gel pattern appeared to be identical to crystalline soybean trypsin inhibitor. Examination of 9 commercial samples of trypsin inhibitor showed multiple bands in all; most samples separated into 6 or more bands, and one preparation resolved into at least 13 bands in the gel. An inhibitor sample isolated by column chromatography and apparently identical to crystalline inhibitor also appeared heterogeneous although it contained fewer minor bands than the commercial samples. Three other trypsin inhibitor fractions recently isolated by column chromatography likewise yielded multiple bands but distinctly different from crystalline soybean trypsin inhibitor. Polyacrylamide-gel electrophoresis appears to be a sensitive tool for examining soybean whey protein fractions and should greatly facilitate future fractionation studies on this complex protein mixture.