ISSN:
1432-1017
Keywords:
Key words Coupling stoichiometry
;
Electrogenicity
;
Slip
;
Calcium pumping
;
Proton ejection
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Physics
Notes:
Abstract A non-equilibrium thermodynamics (NET) model describing the action of completely coupled or `slipping' reconstituted Ca2+-ATPase is presented. Variation of the coupling stoichiometries with the magnitude of the electrochemical gradients, as the ATPase hydrolyzes ATP, is an indication of molecular slip. However, the Ca2+ and H+ membrane-leak conductances may also be a function of their respective gradients. Such non-ohmic leak typically yields `flow-force' relationships that are similar to those that are obtained when the pump slips; hence, caution needs to be exercised when interpreting data of Ca2+-ATPase-mediated fluxes that display a non-linear dependence on the electrochemical proton (Δµ˜H) and/or calcium gradients (Δµ˜Ca). To address this issue, three experimentally verifiable relationships differentiating between membrane leak and enzymic slip were derived. First, by measuring Δµ˜H as a function of the rate of ATP hydrolysis by the enzyme. Second, by measuring the overall `efficiency' of the pump as a function of Δµ˜H. Third, by measuring the proton ejection rate by the pump as a function of its ATP hydrolysis rate.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/s002490050132
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