Purification and characterization of a new dimeric mannose/glucose-binding isolectin from Vicia tetrasperma (L.)...

A new mannose/glucose specific isolectin VTL-II has been purified to electrophoretic homogeneity from the seeds of Vicia tetrasperma (L.) Schreber through successive steps of (i) lectin extraction, (ii) ammonium sulfate fractionation (30-50%), and (iii) affinity chromatography on a column of Sephadex G-50 covalently coupled with D-mannose. The isolectin was found to be a dimeric protein of molecular weight 62 kDa made up of apparently chemically identical subunits unlike the tetrameric isolectins reported earlier from the same plant source. It was found to exhibit (i) 8-16 times higher specificity for rabbit RBC than human RBC, though it showed unspecificity with respect to the different human blood groups, (ii) non-dependence on divalent metal ion for its hemagglutinating activity, (iii) relatively broad pH optimum ranging from pH 7.0 to 8.0, and (iv) thermal inactivation behavior characterized by t(1/2) of 50 degrees C.