Voltage-dependent pump currents of the sarcoplasmic reticulum Ca2(+)-ATPase in planar lipid membranes.
Sarcoplasmic reticulum vesicles containing largely Ca2(+)-ATPase were incorporated into planar lipid membranes. The ATPase was activated by a UV flash-induced concentration jump of ATP from a photolabile caged ATP. Under these conditions stationary pump currents were observed. The dependence of these pump currents on applied voltages was investigated. The current-voltage curve of the Ca2(+)-ATPase shows monotonously increasing pump currents with increasing positive potentials of the ATP containing compartment. This indicates the existence of electrogenic steps in the direction of the transported Ca2+ ions. From the extrapolated reversal potentials of the curve is concluded that less than four positive net charges are transported per hydrolyzed ATP.
Eisenrauch
A
A
Max-Planck-Institut für Biophysik, Frankfurt am Main, FRG.
Bamberg
E
E
D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D000252:Calcium-Transporting ATPases / Q000502:physiology*; D004553:Electric Conductivity; D066298:In Vitro Techniques; D007425:Intracellular Membranes / Q000502:physiology; D008564:Membrane Potentials; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000502:physiology*
D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D000252:Calcium-Transporting ATPases