ISOLATION AND PARTIAL CHARACTERIZATION OF A PORCINE THYROGLOBULIN-BINDING PHASEOLUS-VULGARIS L LECTIN

An albumin lectin from Phaseolus vulgaris L. cultivar Black Turtle Soup (BTS) was purified with porcine thyroglobulin (PTG)-Sepharose affinity chromatography and Sephadex SP-C50-120 ion exchange chromatography. The PTG-binding lectin concentration of BTS bean is 22.5 +/- 0.9 mg g-1 dry flour. The lectin is a tetrameric protein with an estimated molecular weight of 140,000 +/- 9,000, and a sedimentation coefficient of 6.7 S at pH 6.0. The estimated molecular weights of the polypeptide subunits were 37,500, 35,000, 34,500 and 33,500. Isoelectric focusing of the purified lectin revealed three major bands and two minor bands. The isoforms of the lectin focused in a pI range of 5.7-6.3. The partition coefficient of the lectin in a Waters I-250 protein column was 0.25. The lectin contained small concentrations of methionine and no detectable cysteine.