Interpretation of extraordinary kinetics of sodium, potassium
adenosine triphosphatase by a phase change.
Post, Robert L., and Irena Klodos.
Department of Physiology, School of Medicine, University of
Pennsylvania, Philadelphia, PA 19104-6085, USA and Institute of
Biophysics, University of Aarhus, DK 8000 Aarhus, Denmark
APStracts 3:0151C, 1996.
Interpretation of extraordinary kinetics of sodium, potassium
adenosine triphosphatase by a phase change. Am. J. Physiol. -- We
interpret at a molecular level an extraordinary response in the
transient kinetics of the phosphointermediate of Na,K-ATPase (Klodos,
I., R.?L.?Post, and B. Forbush, III. J. Biol. Chem. 269: 1734-1743,
1994). The phosphointermediate comprises two principal states. The
partition between these states varies with salt concentration,
[salt]. A jump in [salt] changes the partition of some of the
molecules more rapidly than they interconvert in a steady state at
constant [salt]. We propose that interconversion is limited by free
volume in the lipid of the surrounding membrane. This lipid is
partitioned into phases which vary with [salt]. Free volume is larger
at the interface between these phases than within the phases
themselves. Na,K-ATPase molecules are distributed at random in the
membrane. When the phase boundary moves in response to a jump in
[salt], it crosses some Na,K-ATPase molecules, which transiently
experience an increase in free volume of the surrounding lipid. Thus
their phosphointermediate states equilibrate more rapidly than at a
constant [salt]. Functional and structural heterogeneity of Na,K
-ATPase molecules is discussed.
Received 24 January 1996; accepted in final form 12 April 1996.
APS Manuscript Number C217-6.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 19 May 96