Differential localization of two isoforms of the regulatory subunit RIIα of cAMP-dependent protein kinase in human sperm: Biochemical and cytochemical study

In the present study, immunogold labeling of ultrathin sections of ejaculated sperm was used to obtain insight into the ultrastructural localization and presumable function of type II cAMP-dependent protein kinase in sperm motion. In the flagellum, a human-specific isoform of the RIIα subunit was located on the axonemal microtubule wall, whereas a different isoform of broader specificity was present in the cytoplasm at the periphery of the coarse fibers and fibrous sheath. This isoform was also found in the mitochondria. The human-specific RIIα subunit is likely linked to microtubules by a unique binding protein of M_r 72kD. These findings are in agreement with the concept of a concerted mechanism involving phosphorylation of both the axonemal microtubules and the fibrous structures for the regulation of mammalian sperm motion. © 1994 Wiley-Liss, Inc.