Characterization of the Surface Glycoproteins of Rat Spermatozoa1

Abstract
The macromolecular composition of a membrane fraction isolated from rat spermatozoa was investigated. Specific biochemical probes were used 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 [sodium dodecyl sulfate] polyacrylamide gels of the isolated membrane fraction revealed a large number of Coomassie Blue staining bands (> 25) and 5 PAS [periodic acid Shiff reagent] 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 labeled by this technique, but no such component is detected on caput epididymal spermatozoa. Similarly, radioactive labeling 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.