Ultrastructural study of separated cell and acrosomal membranes from bull spermatozoa

Ejaculated bull spermatozoa were washed and incubated with a cationic detergent, Hyamine 2389, and the material removed was centrifuged on a three-step sucrose gradient. Five different bands were obtained, three of which contained cell and acrosomal membranes and also acrosomal material. The first of these, band III, was composed of two parts. The lower part contained U-shaped membrane profiles originating from the outer acrosomal membrane, acrosomal material attached to them, and vesicles of different sizes. The upper part, in addition to various vesicles (probably formed from cell membrane), contained acrosomal vesicles arranged in the form of aggregates or caps. The latter vesicles were formed by fusion and vesiculation of the cell and outer acrosomal membranes with tightly bound acrosomal material. Band IV was uniform and comprised various round vesicles with a smooth membrane, which had a typical unit-membrane structure. There were obviously formed from the cell membrane. The fifth band, in the saline portion with material unsedimented in the sucrose, included small vesicles and membrane fragments, the origin of which was obscure. The solubilized material was also left in this fraction.