Four isolectins from the cactus Machaerocereus eruca (ME-C2, D2,E2,F2) have been isolated and purified by hydrophobic and affinity chromatography on a red blood cell stroma column; in their native form there were differences in the molecular weights, whereas in their monomeric form they all showed a repetitive subunit of 35 kDa. The glycan portion of the isolectin which is composed of glucose, galactose, rhamnose, xylose and mannose, represented 20, 24, 26 and 30% of their weight, for ME-C2, D2, E2 and F2, respectively. All four isolectins were closely related in amino acid composition, although the less hydrophobic isolectin contained more glycine and threonine than the more hydrophobic fraction. Hapten inhibition assays indicated that the isolectins possess specificity for d-galactose, N-acetyl-d-galactosamine and galactose-containing glycoproteins and glycopeptides. All the isolectins were capable of suppressing the murine humoral immune response to particulated antigens, although no mitogenic activity in murine lymphocytes was found. The differences found in their physicochemical properties, glycan portion, ability to bind to a hydrophobic gel and amino acid composition suggest that either they are the products ofrelated but distinct genes or the result of different post translational protein processing. © 1991.
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