A MATURATION-RELATED DIFFERENTIAL PHOSPHORYLATION OF THE PLASMA-MEMBRANE PROTEINS OF THE EPIDIDYMAL SPERMATOZOA OF THE HAMSTER BY ENDOGENOUS PROTEIN-KINASES

When the plasma membranes of caput and cauda epididymal spermatozoa of hamster were evaluated for their ability to undergo phosphorylation, a differential phosphorylation of the membrane proteins was observed. In the plasma membranes of the caput epididymal spermatozoa (immature) , twelve proteins were phosphorylated (100, 76, 67, 65, 55, 52, 47, 42 , 38, 32, 30, and 20 kD), whereas in the plasma membranes of cauda epi didymal spermatozoa (mature), a differential phosphorylation pattern w as observed with respect to the 94, 67, 52, and 47 kD proteins. The 94 kD protein was found to be phosphorylated and the 67 kD protein was f ound to be not phosphorylated in cauda spermatozoal plasma membrane (C d SPM) in contrast to this protein in caput spermatozoal plasma membra ne (Cpt SPM). The 52 and 47 kD proteins were also more intensely phosp horylated in Cd SPM than Cpt SPM. The 100 kilodalton protein, although present in both Cpt and Cd sperm plasma membranes, was found to be ph osphorylated at the tyrosine residues only in the Cd SPM, as indicated by the Western blot using antiphosphotyrosine antibody. Further, a di fferential phosphorylation of the substrate proteins present in the Cp t and Cd SPM was seen when Mg2+ in the assay buffer was replaced by ot her divalent cations. For instance, Zn2+ stimulated the phosphorylatio n of an 85 kD protein in cauda SPM and not in the caput SPM and Ca2+ s timulated the phosphorylation of a 76 kD protein only in the cauda SPM . The phosphoproteins in both the plasma membranes were found to be ph osphorylated predominantly at the tyrosine residue. The differential p hosphorylation of a 100 kD protein at tyrosine in the Cd SPM (Western blot), which is absent in the immature Cpt SPM, also indicated that ce rtain proteins in the hamster spermatozoa are phosphorylated in a matu ration-specific manner. (C) 1997 Wiley-Liss, Inc.