Ultrastructural localization of protein kinase C in human sperm

We localized protein kinase C (PKC) in human sperm cells at the ultrastructural level by the immunogold technique. The sperm head PKC was localized in the acrosome, equatorial segment, and post-acrosomal region. In the flagellum, PKC was associated with the segmented column of the neck and was distributed along the mid, principal, and end pieces. Immunoreactive sites were observed in patches along the axoneme and outer dense fibers and were evenly distributed between these regions. Pre-absorption of the antibody used with rat brain PKC (alpha and beta) eliminated gold labeling of the sperm head but only reduced labeling of the sperm tail. The co-localization of PKC with various cytoskeletal and other structural elements suggests that the proteins involved are potential substrates for sperm PKC subspecies. The localization of PKC in distinct structures of the human sperm (head, neck, and tail) strongly suggests a role for this enzyme in various aspects of sperm physiology.