Surface Proteins and Glycoproteins of Ejaculated Bovine Spermatozoa. II. Molecular Composition of the Midpiece and Mainpiece

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Abstract
The midpiece and mainpiece of bovine spermatozoa were fractionated by sucrose density-gradient centrifugation after gentle sonic disruption. The composition of proteins and glycoproteins of the isolated fractions was examined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Some proteins are found in both midpieces and mainpieces while a few are present in midpieces but not in mainpieces. When the gels were stained with 125I-concanavalin A or periodate-Schiff''s stain to visualize glycoproteins, a number of glycoprotein bands were revealed. Surface-labeling with fluorescamine and tritium showed that some of the above glycoproteins and several high MW bands larger than 125,000 are exposed to the sperm surface. The differential composition of surface proteins is likely to reflect the heterogeneous distribution of molecules on the sperm surface and provides evidence of structural and functional differentiation of the sperm surface membrane.