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Dolichos biflorus agglutinin is a glycoprotein with a molecular weight of about 120,000 and consists of 4 subunits of approximately equal size. This lectin has an isoelectric point of about pH 5.5 and a carbohydrate specificity toward a-linked N-acetylgalactosamine. DBA is approximately 5000 times more active in agglutinating blood group A1 cells versus A2 cells, and is used to distinguish these blood types in routine serology. It has also been used to establish secretor status in A1 individuals by hemagglutination inhibition techniques and has potential applications in examining tumors which affect the levels of blood group substances.
Agarose bound* Dolichos Biflorus Agglutinin is prepared from affinity-purified lectin. Heat stable, cross-linked 4% agarose beads with a molecular weight exclusion limit of about 2x107 are used as the solid-phase matrix to which the lectin is covalently bound. The attachment of the lectin to the solid phase is carefully controlled in order to preserve the activity of the lectin as well as to minimize conformational changes of the bound lectin which might result in nonspecific ionic or hydrophobic interactions.
The technique we have developed to couple lectins to agarose provides a very hydrophilic spacer arm between the protein and the matrix. This ensures maximum expression of the carbohydrate binding activity of the lectin. The linkage is very stable over a range of pH values and, unlike cyanogen bromide linkages, proteins are not leached off the gel by Tris or other routinely used buffers. In addition, residual charges generated during cyanogen bromide conjugation which can produce nonspecific binding are not present on the gel following our coupling procedure. |