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Phosphatase activity and potassium transport in liposomes with sodium potassium atpase incorporated






Biochimica et Biophysica Acta 1103(1): 85-93

Phosphatase activity and potassium transport in liposomes with sodium potassium atpase incorporated

We have used liposomes with incorporated pig kidney Na+,K+-ATPase to study vanadate sensitive K+-K+ exchange and net K+ uptake under conditions of acetyl- and p-nitrophenyl phosphatase activities. The experiments were performed at 20.degree. C. Cytoplasmic phosphate contamination was minmized with a phosphate trapping system based on glycogen, phosphorylase a and glucose-6-phosphate dehydrogenase. In the absence of Mg2+ (no phosphatase activity) 5-10 mM p-nitrophenyl phosphate slightly stimulated K+-K+ exchange whereas 5-10 mM acetyl phosphate did not. In the presence of 3 mM MgCl2 (high rate of phosphatase activity) acetyl phosphate did not affect K+-K+ exchange whereas p-nitropheynl phosphate induced a greater stimulation than in the absence of Mg2+; a further addition of 1 mM ADP resulted in a 35-65% inhibition of phosphatase activity with an increase in K+-K+ exchange, which sometimes reached the levels seen with 5 mM phosphate and 1 mM ADP. The net K+ uptake in the presence of 3 mM MgCl2 was not affected by acetyl phosphatase or p-nitrophenyl phosphate, whereas it was inhibited by 5 mM phosphate (with and without 1 mM ADP). The results of this work suggest that the phosphatase reaction is not by itself associated to K+ translocation. The ADP-dependent stimulation of K+-K+ exchange in the presence of phosphatase activity could be explained by the overlapping of one more step/s of the reversible phosphorylation from phosphate with the phosphatase cycle.


Accession: 007650837



Related references

Berberián, G.; Beaugé, L., 1992: Phosphatase activity and potassium transport in liposomes with Na+,K(+)-ATPase incorporated. We have used liposomes with incorporated pig kidney Na+,K(+)-ATPase to study vanadate sensitive K(+)-K+ exchange and net K+ uptake under conditions of acetyl- and p-nitrophenyl phosphatase activities. The experiments were performed at 20 degrees C...

Hokin L.E.; Dixon J.F., 1979: Parameters of reconstituted sodium and potassium transport in liposomes in which purified sodium potassium atpase is incorporated by freeze thaw sonication. Skou, J C And J G Norby (Ed ) Na,k-Atpase: Structure And Kinetics; 2nd International Conference on Properties And Functions Of Na,k-Atpase, Sonderborg, Denmark, Sept 17-21, 1978 Xii+549p Academic Press, Inc : New York, N Y , Usa Illus P47-68

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