Plasma membrane-associated protein tyrosine phosphatase activity in hamster spermatozoa

Plasma membranes of caput and cauda epididymal spermatozoa of hamster exhib ited protein phosphatase activity. This membrane-associated protein phospha tase was identified as a protein tyrosine phosphatase based on its ability to hydrolyse a substrate specific for PTPase, by inhibition of its activity with a specific inhibitor of PTPase (sodium orthovanadate) and by the inab ility to inhibit its activity with calyculin, okadaic acid, trifluoperazine , calcium, EGTA, and EDTA, which ave specific inhibitors of other protein p hosphatases, namely PP-1, PP-2A, PP-2B, and PP-2C respectively. The specifi c activity of the protein tyrosine phosphatase both in the caput and cauda epididymal sperm plasma membranes was similar, implying that the enzyme may not be solely responsible for the differential phosphorylation of membrane proteins observed during maturation (Uma Devi et al. 1997. Mol Reprod Dev 47:341-350). Thus the significance of the PTPase activity in epididymal mat uration still remains to be determined. The membrane-associated PTPase may not be essential for acquisition of motility. However, it appears that the activity is essential for the sustenance of motility since sodium orthovana date, which specifically inhibits PTPase activity also inhibits motility of spermatozoa and decreases the overall velocity of the spermatozoa by decre asing the average path velocity, straight line velocity, curvilinear veloci ty, and amplitude of lateral head displacement of the treated spermatozoa. (C) 1999 Wiley-Liss, Inc.