The difference may arise from experimental differences as, in our approach, isolated and immobilized SPM were used as binding templates for fucose- or LeA-PAA-biotin (each polyacryl-amide-biotin conjugate contains approximately 20 mol% of fucose or LeA). In contrast, Suarez et al. used a bioassay in which unconjugated (free-form) fucose and LeA was used to block live sperm binding to oviductal epithelium. Alternatively, the difference can be due to the different spatial presentations of these two carbohydrates (fucose and LeA) attached to the PAA molecule. The presentation of the sugar residue within a larger molecule determines the binding affinity of the lectin.
Various mono- and oligosaccharides affect the binding affinity of fucose-PAA-biotin to SPM. Fucose, mannose, glucose, and maltose only weakly inhibited this binding. This lack in fucose-binding competition contrasts with the significant inhibitory effect of extracellular fucose on sperm-oviduct binding. Possibly, the absence of inhibition of free fucose on fucose-PAA-biotin binding to SPM is due to conformation of this conjugate that contains four fucose residues.