Characterization of human sperm cell surface components.

Abstract

Intact human sperm, sperm cell lysates, and seminal plasma were radiolabeled by enzymatic iodination with lactoperoxidase and Na’25 L SDS-polyacrylamide gel electrophoresis of labeled sperm surface resolved one minor and four major components with approximate molecular weights of 92, 72, 46, 30, and 20 Kd, respectively. That labeling of intact sperm specifically marked the surface components was supported by experiments in which cell lysates were labeled rather than intact cells. Electrophoresis of labeled sperm cell lysates revealed two major components, both distinct from those detected on the surface of human sperm. To identify components adsorbed to sperm cell surfaces from adnexal secretions, seminal plasma was similarly analyzed. Separation of labeled seminal plasma from both normospermic and vasectomized men resolved five components with approximate molecular weights of 74, 52, 43, 28, and 20 Kd. Three of these coincided with sperm surface components. To identify the chemical composition of the radioiodinated components, labeled sperm surface and labeled seminal plasma were subjected to isopycnic density gradient centrifugation in cesium chloride, a procedure which separates proteins from lipids. With human sperm surface, two areas of radioactivity were resolved, one equilibrium banding with a density characteristic of protein, the other with a density characteristic of lipid. With human seminal plasma, only one area of radioactivity, having a density characteristic of protein, was identified. Electrophoretic analysis of each area of radioactivity obtained from the gradients demonstrated that all of the sperm. surface components and four of the five seminal plasma components were in the protein fractions.