A new assay for functional lectins: the brush border lectin agglutination assay (BBLAA)

Abstract

A new method, the brush border lectin agglutination assay (BBLAA), has been developed to measure the capacity of functional lectins to agglutinate the intestinal brush border membrane. Lectins were incubated with purified chick small intestinal brush border vesicles, agglutinated membrane was isolated by low speed centrifugation and then assayed using alkaline phosphatase as a marker. The brush border agglutination activity of purified plant lectins with various carbohydrate binding specificity was compared. Tomato ( Lycopersicon esculentum) lectin, and wheat germ ( Triticum vulgaris) agglutinin bind N-acetyl- d-glucosamine and were found to have the highest activity. An exponential sigmoid equation fit the data obtained with wheat germ agglutinin, which is consistent with a cooperative mechanism of brush border agglutination. The N-acetyl- d-galactosamine specific lectin from soybean ( Glycine max), and the l-fucose specific lectin from asparagus pea ( Lotus tetragonolobus) had intermediate activity. Of the mixed carbohydrate binding isolectins from red kidney bean ( Phaseolus vulgaris), Pha-E had intermediate activity, and Pha-L no detectable activity. Jack bean ( Canavalia ensiformus) lectin, concanavalin A, (Con A) binds glucose/mannose residues and had marginal activity. Succinylation of con A eliminated brush border agglutination activity. The BBLAA has distinct advantages when compared to other lectin assay systems in that it measures functional agglutination activity directed toward the target membrane on the intestinal epithelium, does not require antibody or enzyme conjugation, and can be used to measure total functional lectins in extracts from diets or meals.