Evonymus europaea lectin precipitated with alpha DGal(1----3) beta DGal(1----4)beta DGlcNAc-bovine serum albumin (BSA), alpha LFuc(1----2)beta DGal(1----3)beta DGlcNAc-BSA, alpha LFuc(1----2)beta DGal(1----4)DGlcNAc, and alpha DGal(1----3)[alpha LFuc(1----2)]beta DGal-BSA. However, the lectin neither precipitated with alpha LFuc(1----2)-beta DGal-BSA, alpha DGal(1----3)beta DGal-BSA, or beta DGal(1----4)beta DGlcNAc-BSA nor agglutinated erythrocytes of Oh phenotype having multiple terminal beta DGal(1----4)beta DGlcNAc residues. These results indicate that the minimal structural requirement for glycoprotein precipitation or cell agglutination by the lectin includes any of the three trisaccharides (fucosylated or nonfucosylated) derived from the blood group B tetrasaccharide. The monosaccharides linked to the beta-D-galactosyl residue in the blood group B tetrasaccharide, namely, alpha-D-galactose, alpha-L-fucose, and N-acetyl-beta-D-glucosamine, participate almost equally in binding to the lectin in as much as removal of any one of these sugars reduces the inhibiting potency of the resulting trisaccharide. alpha LFuc(1----2)beta DGal(1----3)beta DGlcNAc-BSA (H type 1) and alpha LFuc(1----2)beta DGal(1----4)beta DGlcNAc (H type 2) were precipitated to the same extent. The E. europaea lectin neither precipitated alpha DGal(1----4)-beta DGal(1----4)beta DGlcNAc-BSA, Lea-BSA, Leb-BSA, or beta DGlcNAc(1----4)[alpha LFuc(1----6)]beta DGlcNAc-BSA nor agglutinated Oh,Lea and Oh,Leb erythrocytes, demonstrating that terminal D-galactose linked alpha-(1----4) to subterminal beta-D-galactose, or alpha-L-fucose linked to N-acetylglucosamine, prevents lectin binding. Corey-Pauling-Koltun molecular models, built on the basis of data from 1H NMR and hard-sphere exo-anomeric (HSEA) calculations provided by Lemieux and co-workers [Lemieux, R. U., Bock, K., Delbaere, L. T. J., Koto, S., & Rao, V. S. (1980) Can. J. Chem. 58, 631-653], show that these alpha-D-galactosyl and alpha-L-fucosyl groups act to sterically hinder lectin binding to these oligosaccharides; these observations also suggest that the lectin binds to the beta-side of these oligosaccharides. These sides, on both blood group H type 1 and blood group H type 2 oligosaccharides, provide a similar contour which can fully account for their equal reactivity with E. europaea lectin. The only difference found between Lotus and Ulex I lectins in precipitating ability was that only Lotus precipitated with beta DGlcNAc(1----4)[alpha LFuc(1----6)]beta DGlcNAc-BSA.(ABSTRACT TRUNCATED AT 400 WORDS)