Conformational changes of Na,K-ATPase probed with eosin Y

Area of Science:

• Biochemistry
• Enzyme kinetics
• Biophysical chemistry

Background:

• Na,K-ATPase (sodium-potassium adenosine triphosphatase) is a crucial ion pump in cell membranes.
• Understanding cation interactions with Na,K-ATPase is vital for cellular physiology.
• Fluorescent probes offer sensitive methods for studying enzyme dynamics.

Purpose of the Study:

• To investigate the thermodynamic and kinetic parameters of cation binding to Na,K-ATPase.
• To characterize the interaction using the fluorescent dye eosin Y.
• To elucidate the binding mechanism and its dependence on enzyme conformation.

Main Methods:

• Time-resolved fluorescence spectroscopy.
• Stopped-flow fluorometry.
• Fluorescence binding studies with eosin Y and various cations.

Main Results:

• Eosin Y binding to Na,K-ATPase was observed, indicated by a 3 ns fluorescence decay.
• Cation binding, requiring mono- and divalent cations, was characterized as a nonselective electrostatic interaction.
• Eosin Y binding occurred specifically when the enzyme was in the F1 conformational state.
• Kinetic parameters for eosin Y binding were successfully determined.

Conclusions:

• Eosin Y serves as a sensitive reporter for cation binding to Na,K-ATPase.
• The enzyme possesses high-affinity binding sites for eosin Y mediated by negatively charged groups, revealed by cation presence.
• Cation binding is conformation-dependent, occurring in the F1 state, suggesting a role in enzyme regulation.