NDLI: Mechanism of Mg2+ Binding in the Na+,K+-ATPase

Content Provider	PubMed Central
Author	Anne, Pilotelle-bunner Cornelius, Flemming Sebban, Pierre Kuchel, Philip W. Clarke, Ronald J.
Copyright Year	2009
Abstract	The Mg2+ dependence of the kinetics of the phosphorylation and conformational changes of Na+,K+-ATPase was investigated via the stopped-flow technique using the fluorescent label RH421. The enzyme was preequilibrated in buffer containing 130 mM NaCl to stabilize the E1(Na+)3 state. On mixing with ATP, a fluorescence increase was observed. Two exponential functions were necessary to fit the data. Both phases displayed an increase in their observed rate constants with increasing Mg2+ to saturating values of 195 (± 6) s−1 and 54 (± 8) s−1 for the fast and slow phases, respectively. The fast phase was attributed to enzyme conversion into the E2MgP state. The slow phase was attributed to relaxation of the dephosphorylation/rephosphorylation (by ATP) equilibrium and the buildup of some enzyme in the E2Mg state. Taking into account competition from free ATP, the dissociation constant (K d) of Mg2+ interaction with the E1ATP(Na+)3 state was estimated as 0.069 (± 0.010) mM. This is virtually identical to the estimated value of the K d of Mg2+-ATP interaction in solution. Within the enzyme-ATP-Mg2+ complex, the actual K d for Mg2+ binding can be attributed primarily to complexation by ATP itself, with no apparent contribution from coordination by residues of the enzyme environment in the E1 conformation.
Related Links	http://dx.doi.org/10.1016/j.bpj.2009.01.042
Ending Page	3761
Page Count	9
Starting Page	3753
File Format	PDF
ISSN	00063495
e-ISSN	15420086
Journal	Biophysical Journal
Issue Number	9
Volume Number	96
Language	English
Publisher	The Biophysical Society
Publisher Date	2009-05-01
Access Restriction	Open
Rights Holder	The Biophysical Society
Subject Keyword	Biophysics Research in Higher Education
Content Type	Text
Resource Type	Article
Subject	Biophysics

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