Characterization of the Surface Glycoproteins of Rat Spermatozoa1

Abstract

The present study investigates the macromolecular composition of a membrance fraction isolated from rat spermatozoa and uses specific biochemical probes to study the externally oriented plasma membrane glycoproteins of caput and cauda epididymal spermatozoa. A highly purified membrane fraction was isolated from rat cauda epididymal spermatozoa using sonication and differential centrifugation. SDS polyacrylamide gels of the isolated membrane fraction revealed a large number of Coomassie Blue staining bands (>25) and 5 PAS positive bands. The galactose oxidase-[3H]sodium borohydride technique was employed on intact spermatozoa to radioactively label externally oriented plasma membrane glycoproteins possessing terminal galactose or galactosamine residues on their oligosaccharide chains. Cauda epididymal spermatozoa possess a 37,000 dalton glycoprotein on the cell surface which is labelled by this technique, but no such component is detected on caput epididymal spermatozoa. Similarly, radioactive labelling of surface sialo-glycoproteins by sequential treatment of spermatozoa with sodium metaperiodate and [3H]sodium borohydride revealed that the 37,000 dalton glycoprotein could be labeled on cauda epididymal spermatozoa, but is not detected on caput epididymal spermatozoa. The significance of these results with respect to maturation of spermatozoa in the epididymis is discussed.