The nature of lectins from Dolichos lablab.

ABSTRACT

The lectins from the seeds of Dolichos lablab var. lignosus (field bean) and Dolichos lablab var. typicus (lablab bean) have been isolated in a homogeneous form by affinity chromatography on D-mannose linked Sepharose. Both the lectins are glycoproteins and have a molecular weight of 60,000 and S 20,w value of 5·2 and seem to be made up of 4 similar subunits (apparent molecular weight 15,000). The carbohydrate content ofthe lectins is mostly fucose (2-5 mol per mol of protein), mannose (5-8 mol per mol of protein) and N-acetyl glucosamine (1–2 mol per mol of protein). The amino acid composition of both the lectins was similar and methionine and half cystine could not be detected, Both the lectins have similar tryptic peptide map. Alanine and serine were the only Ν and C-terminal amino acids for both lectins. The lectins were found to contain low amounts of bound metals such as manganese, magnesium and calcium. The near ultra-violet circular dichroism spectra of the lectins are similar to that of Sainfoin. Circular dichroism data indicate that tyrosine and tryptophan residues are involved in sugar binding. The lectins are nonspecific for human blood groups and they agglutinate a variety of other erythrocytes. Among a number of sugars, D-glucose and D-mannose inhibited the haemagglutinating activity of the lectins. The lectins were antigenically similar.