Restriction of a sperm surface antigen's mobility during capacitation

Abstract

Fluorescent Fab 1 1 Abbreviations used: Fab, immunoglobulin G (IgG) fragment with antigen binding capacity from papain digestion of IgG; MGP, rabbit sperm plasma membrane glycoprotein; AMGP, guinea pig antimembrane glycoprotein globulin; Fl-AMGP, fluorescein-conjugated AMGP; AMGP-Fab, Fab fragment of IgG from AMGP globulin; Control-Fab, Fab fragment of IgG from globulin of guinea pigs injected with Freund's complete adjuvant and saline; Fl-AIgG, Fluorescein-conjugated rabbit IgG antiguinea pig IgG. [immunoglobulin G (IgG) fragment with antigen binding capacity from papain digestion of IgG] antibody fragments and globulin from antisera prepared against a single rabbit sperm surface membrane glycoprotein antigen (MGP) were used to study surface antigen mobility. Epididymal and ejaculated spermatozoa exhibited a redistribution of MGP surface antigen over the acrosomal region when labeled at 4°C and warmed to 37°C. Following in vivo capacitation, spermatozoa did not exhibit MGP surface antigen redistribution over the acrosome. The restricted mobility of this surface antigen implies a physiological change in plasma membrane fluidity, which may be a necessary preliminary to the acrosome reaction. Furthermore, it is suggested that the presence or absence of specific peripheral membrane proteins may control the positional relationship between mobile and nonmobile integral membrane components.