Phosphorylation of external cell-surface proteins by an endogenous ecto-protein kinase of XXXX epididymal intact spermatozoa.

@entity6000 @entity8262 @entity1391 @entity1919 @entity563 @entity1889 @entity1237 @entity855
Intact spermatozoa from @entity1237 cauda epididymides possess an ecto-( @entity1919 -independent protein kinase) activity that causes transfer of the terminal @entity1391 of exogenously added [gamma-32P]ATP to the @entity563 and @entity1889 residues of several endogenous plasma-membrane phosphoproteins located on the external cell surface. @entity1919 , @entity8262 , calmodulin and muscle @entity1919 -dependent protein kinases I and II had no appreciable effect on the rate of phosphorylation of ecto-proteins by the intact cells. The ecto-enzyme is not derived from the catalytic subunit of a @entity1919 -dependent kinase. Sperm ecto-kinase activity is not due to contamination of broken cells or any possible cell damage during incubation and isolation of spermatozoa. The phosphorylation reaction was linear for approx. 1 min and there was no detectable uptake of @entity855 by these cells. The activity of the ecto-kinase was strongly inhibited by proteinases and by the membrane-nonpenetrating surface probes. The products of the reaction were associated with the intact cells and the 32P of the labelled cells was largely lost when treated with @entity6000 or proteinases: trypsin and pronase. These data are consistent with the view that the observed protein kinase and the phosphoproteins are located on the external surface of spermatozoa. Vigorously forward-motile whole spermatozoa showed a relatively high capacity to phosphorylate ecto-proteins that undergo rapid turnover. The results suggest the occurrence of a novel coupled-enzyme system (ecto-protein kinase and phosphoprotein phosphatase) on the sperm external surface that may modulate sperm physiology by determining the phosphorylated states of the ecto-proteins.
