| Popis: |
Charge translocation associated with partial reactions of the Na,K-pump may be studied by fast perturbation methods. After an ATP concentration-jump, transient currents can be recorded in a compound membrane system consisting of flat Na,K-ATPase membrane fragments bound to a planar lipid bilayer acting as a capacitive electrode. The electrical signals, which can be suppressed by inhibitors of the Na,K-ATP-ase, require the presence of Na+ but not of K+ in the aqueous medium. From the recorded current signal, the intrinsic pump current can be evaluated. Information on the nature of the electrogenic reaction steps can be obtained by a chymotrypsin modification of the protein, by which the release of sodium ions to the extracellular side is blocked. These and other experiments lead to the conclusion that the transient pump-currents result from charge translocation associated with deocclusion of trapped sodium ions, followed by release of Na+ to the extracellular medium. |
