The isolation of two proteins, glycoprotein I and a trypsin inhibitor, from the seeds of kidney bean (Phaseolus vulgaris)

Abstract

The isolation of 2 proteins from the seeds of kidney bean is described. The individual steps in the purification procedure included: extraction of the seeds at pH 9.0, dialysis, 1st against pH 9.0 and then against pH 5.0 buffers, high-voltage electro-phoresis of the proteins soluble at pH 5.0 and chromatography on Sephadex G-200, Sephadex G-75 and DEAE-Sephadex columns. Of the 2 proteins isolated, the 1st and larger component was a glycoproteln and its carbohydrate part was mainly composed of D-mannose and D-glucosamine together with smaller amounts of arabinose, xylose and fucose. The 2nd protein component isolated was a trypsin inhibitor and was almost entirely devoid of sugars but contained a firmly bound pinkish-blue pigment. The amino acid composition of the 2 proteins was determined. The glycoproteln contained very little if any cyst(e)ine but was relatively rich in aromatic amino acids, whereas the trypsin inhibitor had an unusually high cystine content (nearly 15%) but was relatively poor in valine and in aromatic amino acids.