Purification and some properties of Phaseolus mungo lectin

Abstract

Phaseolus mungo lectin in pure form was isolated from seeds by affinity chromatography on a galactosyl Sepharose 6B column. The lectin contained 8.3% neutral carbohydrate. It absorbed maximally near 278 nm, and the corresponding maxima in fluorescence excitation and emission spectra occurred, respectively, at 278 and 337 nm. Its elution profile from an analytical Sephadex G-150 column was consistent with a molecular weight of 137 000 and a Stokes radius of 4.3 nm; the frictional ratio, f/f0, of the lectin was calculated to be 1.26. The lectin moved as a single protein band of Mr 66 000 in SDS-PAGE under both reducing and nonreducing conditions. The results suggested that the lectin is a dimer whose overall native conformation is nearly globular. From the effect of 10 saccharides on the hemagglutinating activity of lectin against trypsinized rabbit erythrocytes, it was concluded that the lectin was galactose/N-acetylgalactosamine-specific, having significantly reduced affinity for N-acetylgalactosamine. The lectin showed preference for alpha-glycoside and probably does not contain a hydrophobic binding site.