Alteration of goat sperm ecto-phosphoprotein phosphatase activity and its distribution on the sperm surface during epididymal maturation

Abstract

Phosphoprotein phosphatase (ecto-PPase) of goat epididymal sperm outer surface showed a significant increase in its activity at the initial stage of epididymal sperm maturation (up to the proximal corpus region) followed by a sharp fall towards the terminal phase of the maturation event. PPase activity showed nearly the same profile when estimated in intact cells as well as in isolated sperm plasma membrane. The ecto-PPase was purified to apparent homogeneity by using various biochemical fractionation procedures, such as solubilization with Triton X-100, sephadex gel filtration chromatography, concanavalin A–sepharose affinity chromatography and diethylaminoethyl–cellulose ion-exchange chromatography. The isolated PPase has a molecular mass of approximately 36 kDa and an isoelectric point of 5.95. Sperm surface topography of the enzyme was investigated using fluorescein isothiocyanate-conjugated antibody of the purified PPase. The immunofluorescent studies have demonstrated that the isolated PPase is localized on the external surface of viable sperm. Immunocytochemical studies also revealed a marked topographical alteration of ecto-PPase during epididymal transit of the male gametes. Immunoreactivity was observed all over the surface of caput sperm, but was restricted primarily to the anterior tip of the head in the corpus sperm and to the posterior part of the head in cauda sperm cells. The maturation-dependent decrease in PPase activity was also confirmed by immunofluorescent studies. This remarkable maturation-dependent modification of ecto-PPase activity, as well as its distribution on sperm surface, suggest that the ecto enzyme may play an important role in sperm function by regulating the phosphorylation states of the membrane-associated and reproductive fluid phosphoprotein substrates.