ISOLATION AND GENERAL PROPERTIES OF LECTINS FROM THE BEAN (PHASEOLUS VALGARIS VAR. ROSINHA G2)

Abstract

A purified lectin was prepared from 0.15 M NaCl extracts of bean (Phaseolus vulgaris var. Rosinha G2) by affinity chromatography on ConA-Sepharose followed by gel chromatography on Sephadex G-200. The haemagglutining material isolated by affinity chromatography (CII-Af) contained at least three active protein bands as shown by polyacrylamide gel electrophoresis. By chromatography on a Sephadex G-200 column, the (CII-Af) fraction gave only a major peak (CII-β) with haemagglutininating activity, which showed a single broad band on gel electrophoresis. Gel isoelectric focusing of the CII-β component gave a single active band in the pH range of 5.5–5.7. The purified lectin was a glycoprotein, containing 8.30% of neutral sugars (as mannose) and 2.12% of hexosamine (as glucosamine) and only trace amounts of sulphur-containing amino acids. The protein had a MW of 136,000 (6.9 S) with a Stokes radius of 43 A, a calculated diffusion constant (D20,w) of 5 times 10−7 cm2 s−1, and a partial specific volume (v) of 0.75 ml.g−1. From its frictional ratio f/fo = 1.3 and assuming a hydration capacity of 0.3 to 0.4 g of water/g of protein, the axial ratio for the lectin molecule would be in the range of 3–4 if a prolate ellipsoid of revolution is chosen as a model.