Thomas D. Noland

Substructure of the postacrosomal sheath of bovine spermatozoa.

The substructure of the postacrosomal sheath and its relationship to the plasma membrane and nuclear membrane complex were examined in thin-section, negative-stain, surface-replica, and freeze-fracture preparations. The matrix of the postacrosomal sheath contains a single layer of closely associated 10- to 12-nm filamentous elements aligned parallel to the long axis of the sperm. A precise lateral interaction of the filaments is suggested from negative-stain images which reveal a second set of parallel striations extending over the surface of the sheath at 60 degrees relative to the filament long axis. Several structural differences between the posterior and anterior segments and the outer and inner surface of the postacrosomal sheath were identified. Data on structural specializations of the plasma membrane and nuclear membrane complex which relate to the asymmetric structure are presented and their potential significance in fertilization events discussed.

Testicular membranes with improved stability of the gonadotropin receptor

A plasma membrane fraction has been prepared from rat testis using an aqueous double-phase polymer system containing dextran, poly(ethylene glycol) 6000 and Zn2+. The membrane-associated gonadotropin receptor for lutropin and human choriogonadotropin can be markedly stabilized by a thawing-washing step of frozen membranes which prolongs the apparent half-life of the unoccupied membrane-associated receptors from less than 1 h at 37 degrees C to greater than 5h. Also, no degradation of 125I-labeled human choriogonadotropin was detected following incubation with the membrane fraction. The equilibrium binding was characterized by an apparent association constant of 1.6 x 10(10) M-1 and a receptor content of 33 fmol/mg protein. Binding kinetics yielded as association rate constant of 1.0 x 10(8) M-1 x min-1, while the dissociation rate constant for human choriogonadotropin was too low to be accurately determined under the conditions used. In contrast, ovine lutropin could be reversibly bound to the membranes leaving the previously occupied receptors available for binding by 125I-labeled human choriogonadotropin.