In this study, we have developed a new assay to biochemically quantify carbohydrate affinity of the apical head plasma membrane of bovine sperm. The SPM was purified and immobilized and biotinylated carbohydrate probes were used for quantitative detection of binding as well as binding competition. The effects of in vitro capacitation factors such as bicarbonate and heparin, as well as endogenous proteoglycans present in the follicular fluid and oviduct, on regulation of carbohydrate affinity were tested.
The assay confirmed involvement of fucose in the sperm-oviduct binding in the bovine species and suggested a role for man-nan in this binding. The relevant carbohydrate binding sites appear to be exclusively localized in the apical tip of the sperm head surface area of uncapacitated bovine sperm cells, and not only the sugar but also the sugar conformation seems to be an important binding factor. We should consider here that we visualized the binding of multivalent biotinylated carbohydrate probes on living sperm cells, which may well cause patching or capping of the sperm lectins of interest.