The effect of cytoplasmic K+ on the activity of the Na+/K(+)-ATPase.
Experiments with the reconstituted (Na+ + K+)-ATPase show that besides the ATP-dependent cytoplasmic Na(+)-K+ competition for Na+ activation there is a high affinity inhibitory effect of cytoplasmic K+. In contrast to the high affinity K+ inhibition seen with the unsided preparation at a low ATP especially at a low temperature, the high affinity inhibition by cytoplasmic K+ does not disappear when the ATP concentration an-or the temperature is increased. The high affinity inhibition by cytoplasmic K+ is also observed with Cs+, Li+ or K+ as the extracellular cation, but the fractional inhibition is much less pronounced than with Na+ as the extracellular cation. The results suggest that either there are two populations of enzyme, one with the normal ATP dependent cytoplasmic Na(+)-K+ competition, and another which due to the preparative procedure has lost this ATP sensitivity. Or that the normal enzyme has two pathways for the transition from E2-P to E1ATP. One on which the enzyme with the translocated ion binds cytoplasmic K+ with a high affinity but not ATP, and another on which ATP is bound but not K+. A kinetic model which can accommodate this is suggested.
Cornelius
F
F
Institute of Biophysics, University of Aarhus, Denmark.
Skou
J C
JC
D000255:Adenosine Triphosphate / Q000378:metabolism; D001667:Binding, Competitive; D003593:Cytoplasm / Q000201:enzymology* / Q000378:metabolism; D003902:Detergents; D004789:Enzyme Activation; D011188:Potassium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
D003902:Detergents; D000255:Adenosine Triphosphate; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium