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Biophys J, May 1998, p. 2285-2298, Vol. 74, No. 5

Fast Transient Currents in Na,K-ATPase Induced by ATP Concentration Jumps from the P3-[1-(3',5'-Dimethoxyphenyl)-2-Phenyl-2-Oxo]ethyl Ester of ATP

Valerij S. Sokolov,*# Hans-Jürgen Apell,* John E. T. Corrie,§ and David R. Trentham§

 *Department of Biology, University of Konstanz, Konstanz, Germany;  #A. N. Frumkin Institute of Electrochemistry, Academy of Sciences of Russia, Moscow, Russia; and  §National Institute for Medical Research, Mill Hill, London NW7 1AA, England

Electrogenic ion transport by Na,K-ATPase was investigated by analysis of transient currents in a model system of protein-containing membrane fragments adsorbed to planar lipid bilayers. Sodium transport was triggered by ATP concentration jumps in which ATP was released from an inactive precursor by an intense near-UV light flash. The method has been used previously with the P3-1-(2-nitrophenyl)ethyl ester of ATP (NPE-caged ATP), from which the relatively slow rate of ATP release limits analysis of processes in the pump mechanism controlled by rate constants greater than 100 s-1 at physiological pH. Here Na,K-ATPase was reinvestigated using the P3-[1-(3,5-dimethoxyphenyl)-2-phenyl-2-oxo]ethyl ester of ATP (DMB-caged ATP), which has an ATP release rate of >105 s-1. Under otherwise identical conditions, photorelease of ATP from DMB-caged ATP showed faster kinetics of the transient current compared to that from NPE-caged ATP. With DMB-caged ATP, transient currents had rate profiles that were relatively insensitive to pH and the concentration of caged compound. Rate constants of ATP binding and of the E1 to E2 conformational change were compatible with earlier studies. Rate constants of enzyme phosphorylation and ADP-dependent dephosphorylation were 600 s-1 and 1.5 × 106 M-1 s-1, respectively, at pH 7.2 and 22°C.

Biophys J, May 1998, p. 2285-2298, Vol. 74, No. 5
© 1998 by the Biophysical Society   0006-3495/98/05/2285/14  $2.00


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