Occurrence of an ecto-phosphoprotein phosphatase in goat epididymal spermatozoa

Intact spermatozoa from goat cauda epididymis possess phosphoprotein phosphatase activity that causes dephosphorylation of externally added [32p]histones. The enzymic reaction was linear with time for at least 15 min and there was little uptake of [32p]histones by these cells. The activity of the enzyme of the whole spermatozoa was not due to contamination of the broken cells or epididymal plasma and leakage of the intracellular enzymic activity during incubation. The activity of the phosphoprotein phosphatase was strongly inhibited by the thiol reagent: p-chloromercuribenzenesulfonic acid, which is believed not to enter the cells. There was no appreciable loss of the enzymic activity from the cells when washed with EDTA (2.0 mM) or a hyperosmotic medium. These data are consistent with the view that the observed activity of the enzyme is located on the spermatozoal external surface. Studies with unlabelled p-nitrophenyl phosphate and beta-glycerophosphate indicate that the sperm ecto-enzyme is not a non-specific phosphatase.