Regional differences in distribution of surface proteins over the bull spermatozoa.

Surface-radioiodinated bull spermatozoa were ultrasonicated and fractionated by Percoll-gradient centrifugation. The different fractions obtained were solubilized and analyzed by SDS-polyacrylamide gel electrophoresis. Three fractions containing sperm heads, midpieces, and membranes and small fragments of the principal pieces were obtained. The electrophoresis revealed 5 main peaks representing the radioiodinated surface proteins with molecular weights of 80 000-90 000 (Ia), 68 000-75 000 (Ib), 42 000-47 000 (II), 33 000-37 000 (III) and 15 000-18 000 (V) from the intact spermatozoa as well as from each sperm fragment fraction. The major differences between fractions were in the relative magnitudes of the peaks. The peak II characteristically dominated in the head fraction, but was very small in the midpiece fraction. The results from the present study suggest that the peak II seen in the intact spermatozoa is mainly located on the head plasma membrane and that the differences in the sperm surface properties may be due to the uneven distribution or surface exposure of the proteins.