Occurrence of a coupled-enzyme system on the intact-sperm outer surface that phosphorylates and dephosphorylates ecto-proteins.
Goat cauda-epididymal intact sperm ecto [32P] proteins phosphorylated in presence of exogenous [gamma-32P]ATP by an endogenous ecto-cyclic AMP-independent protein kinase (CIK), have been found to lose 32P when the labelled cells are incubated at 37 degrees C in a modified Ringer's solution. Analysis of the 32P-labelled products of the turnover of the ecto-phosphoproteins show that 32Pi rather than 32P-labelled peptides, is released from the cell-surface phosphoproteins indicating that the turnover of the ecto-phosphoproteins is mediated by an endogenous sperm outer-surface phosphoprotein phosphatase (ecto-PPase). The ecto-PPase is not a non-specific phosphatase since unlabelled p-nitrophenyl phosphate, beta-glycerophosphate or ATP at a relatively high concentration (1 mM each) has no appreciable effect on the dephosphorylation of the cell-surface proteins. The intact-sperm ecto-proteins phosphorylated and then dephosphorylated by the endogenous ecto-CIK and PPase respectively, undergo rephosphorylation by the cell-surface CIK. The data are consistent with the view that sperm external surface possesses a novel coupled-ecto-CIK and PPase enzyme system that regulates the phosphorylated states of the intact-sperm ecto-proteins by a cyclic mechanism of protein phosphorylation and dephosphorylation.
Barua
M
M
Indian Institute of Chemical Biology, Calcutta.
Haldar
S
S
Majumder
G C
GC
D000818:Animals; D004590:Electrophoresis, Paper; D006041:Goats; D007700:Kinetics; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism*; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D013094:Spermatozoa / Q000201:enzymology*
D008565:Membrane Proteins; D010750:Phosphoproteins; D011494:Protein Kinases; D010749:Phosphoprotein Phosphatases