The Na+,K+-ATPase carrying the carboxy-terminal Ca2+/calmodulin binding domain of the Ca2+ pump has 2Na+,2K+ stoichiometry and lost charge movement in Na+/Na+ exchange.
An altered ion-transport stoichiometry from 3Na+,2K+ to 2Na+,2K+ is observed in a chimeric Na+,K+ATPase, which carries the Ca2+/calmodulin binding domain (CBD) of the plasma membrane Ca2+-ATPase at its carboxy-terminus [Zhao et al., FEBS Lett. 408 (1997) 271-2751. The ouabain-resistant mutant of this chimera (ORalpha1-CBD) was constructed to further investigate the effect of the CBD on ion-transport properties. The ORalpha1-CBD still shows the 2Na+,2K+ stoichiometry. The loss of electrogenicity is accompanied by the disappearance of transient charge movements in the Na+/Na+ exchange mode. We conclude that the binding of the third Na+ ion, but not of the two others, in 3Na+,2K+ transport mode apparently senses the electric field, and that the voltage-dependent Na+ binding is likely to be lost in the chimera with CBD.
Yoshimura
S H
SH
Max-Planck-Institut für Biophysik, Frankfurt, Germany.
Vasilets
L A
LA
Ishii
T
T
Takeyasu
K
K
Schwarz
W
W
D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000187:drug effects / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism*; D002645:Chickens; D016297:Mutagenesis, Site-Directed; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000737:chemistry*; D012413:Rubidium / Q000378:metabolism; D012964:Sodium / Q000737:chemistry* / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014101:Torpedo; D014982:Xenopus laevis
D002147:Calmodulin; D010042:Ouabain; D012964:Sodium; D000252:Calcium-Transporting ATPases; D000254:Sodium-Potassium-Exchanging ATPase; D012413:Rubidium; D011188:Potassium; D002118:Calcium