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Pre-steady-state charge translocation in NaK-ATPase from eel electric organ
K Fendler1, S Jaruschewski, A Hobbs
1Max-Planck-Institute für Biophysik, Frankfurt, Germany.
The Journal of General Physiology
|October 1, 1993
Summary
This study investigates the NaK-ATPase enzyme
Area of Science:
- Biochemistry
- Biophysics
- Enzyme kinetics
Background:
- The NaK-ATPase enzyme plays a crucial role in cellular ion transport.
- Understanding its reaction cycle is vital for comprehending cellular energy transduction.
Purpose of the Study:
- To elucidate the pre-steady state kinetics of NaK-ATPase.
- To characterize charge translocation and phosphorylation during the enzyme's reaction cycle.
Main Methods:
- Time-resolved measurements of charge translocation using adsorbed microsomes on lipid bilayers.
- Rapid acid quenching technique to study phosphoenzyme formation kinetics.
- Kinetic modeling based on the Albers-Post cycle.
Main Results:
- Identified distinct phases in the enzyme's electrical signal.
- Correlated relaxation times with ATP binding/exchange and phosphorylation.
- Determined a rate constant for the electrogenic E1P-->E2P transition (> or = 1,000 s-1).
Conclusions:
- Proposed a kinetic model for NaK-ATPase pre-steady state.
- Confirmed ATP binding/exchange and phosphorylation precede the E1P-->E2P transition.
- Provided insights into the electrogenic nature of the NaK-ATPase reaction cycle.