Purification and Partial Characterization of a Lectin from Phaseolus vulgaris

A method is presented for the isolation of a lectin from a Brazilian cultivar of the common bean (Phaseolus vulgaris L.), through extraction in acidic (pH 4.2) medium, fractionation with ammonium sulfate, and chromatography on DEAE-cellulose. The lectin was shown to be homogeneous by gel electrophoresis and isoelectric focusing.The molecular weight, determined by osmometry, is 100,250 daltons; the isoelectric point, determined by isoelectric focusing, is pH 5.1; and the extinction coefficient at 280 nm and pH 7 is E(1%) (1 cm) = 7.85.The lectin was shown to be a glycoprotein with 9.11% of neutral sugars and 1.44% of amino sugars. Its amino acid composition was characterized by the absence of methionine and a very low content of half-cystine, with a predominance of acidic and hydroxylated amino acids.The lectin presented no specificity when tested with red blood cells of all the groups of the ABO system.