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Dephosphorylation Kinetics of Pig Kidney Na+,K+-ATPase

MPS-Authors
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Kane,  David J.
Department of Biophysical Chemistry, Max Planck Institute of Biophysics, Max Planck Society;

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Grell,  Ernst
Department of Biophysical Chemistry, Max Planck Institute of Biophysics, Max Planck Society;

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Bamberg,  Ernst
Department of Biophysical Chemistry, Max Planck Institute of Biophysics, Max Planck Society;

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Clarke,  Ronald J.
Department of Biophysical Chemistry, Max Planck Institute of Biophysics, Max Planck Society;

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Citation

Kane, D. J., Grell, E., Bamberg, E., & Clarke, R. J. (1998). Dephosphorylation Kinetics of Pig Kidney Na+,K+-ATPase. Biochemistry, 37(13), 4581–4591-4581–4591. doi:10.1021/bi972813e.


Cite as: http://hdl.handle.net/21.11116/0000-0007-A1E0-5
Abstract
The kinetics of K+-stimulated dephosphorylation of the Na+,K+-ATPase were investigated at pH 7.4, 24 degrees C, and an ATP concentration of 1.0 mM via the stopped-flow technique using the fluorescent label RH421. Two different mixing procedures were used: (a) premixing with ATP to allow phosphorylation to go to completion, followed by mixing with KCl; and (b) simultaneous mixing with ATP and KCl. Using mixing procedure (a), the dephosphorylation rate constant of enzyme complexed with K+ ions could be determined directly to be </=366 s-1 and the rate constant for spontaneous dephosphorylation (without K+) </=60 s-1. The K+ concentration dependence of the observed reciprocal time constant showed half-saturation at a K+ concentration of 2.4-2.6 mM with positive cooperativity involved in the occupation of the K+ binding sites on the E2P conformation of the enzyme. Using mixing procedure (b), it was found that at saturating K+ concentrations the dephosphorylation of the enzyme is rate-limited by its phosphorylation, which occurs with a rate constant of approximately 190 s-1 (1). These results show that all reactions occurring after phosphorylation and prior to dephosphorylation, i.e., the E1P to E2P conformational transition as well as Na+ release and K+ binding steps, must be fast (>190 s-1).