Partial Reaction Chemistry and Charge Displacement by the Fungal Plasma-Membrane H+-Atpase
Over the past five years, progress in understanding primary charge-displacement reactions in electrogenic ion pumps has come largely from studies on the sodium pump enzyme, the so-called Na+,K+-ATPase. This multiple-ion transporter/exchanger has been shown to occlude both sodium and potassium ions during the transport cycle, and to effect the major charge displacement either during sodium deocclusion or in a debinding step immediately following deocclusion. For kinetic reasons (Nakao & Gadsby, 1986; Sturmer et al., 1991; Gadsby et al., 1993) the sodium pump is now viewed as an ion-activating mechanism operating in series with a high-resistance transmembrane channel, such that the juncture between the two would serve as an ion well, exactly in the sense propounded by Mitchell (1969) for the F-type ATPases, to convert energy of electric fields into energy of chemical concentrations.
KeywordsMembrane Voltage Pump Current Charge Displacement Proton Wire Equilibrium Voltage
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