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Two bacteriorhodopsin M intermediates differing in accesibility of the Schiff base for azide
1Department of Photobiochemistry, A.N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow, Russian Federation.
FEBS Letters
|June 3, 1996
Summary
Glutaraldehyde and LuCl3 inhibit M intermediate decay in bacteriorhodopsin (bR). These agents shift equilibrium towards a less accessible M form, supporting azide
Area of Science:
- Biochemistry
- Photochemistry
- Membrane Proteins
Background:
- Bacteriorhodopsin (bR) is a light-driven proton pump.
- The M intermediate is a key state in the bR photocycle.
- Understanding M intermediate decay mechanisms is crucial for bR function.
Purpose of the Study:
- To investigate the effects of glutaraldehyde, LuCl3, glycerol, and sucrose on M intermediate decay in wild-type and D96N mutant bacteriorhodopsin.
- To elucidate the mechanism of azide action in M intermediate decay.
- To differentiate between proposed models of azide interaction with bR.
Main Methods:
- Spectroscopic analysis of M intermediate decay kinetics in wild-type and D96N mutant bacteriorhodopsin.
- Inhibition studies using glutaraldehyde, LuCl3, glycerol, and sucrose.
- Azide concentration-dependent M decay measurements.
Main Results:
- Glutaraldehyde and LuCl3 inhibit M intermediate decay in both wild-type and D96N mutant bR.
- LuCl3 is a more potent inhibitor than glutaraldehyde.
- Glycerol and sucrose also inhibit M decay.
- Inhibitors shift azide concentration dependency to higher concentrations without altering linearity.
- Data support an equilibrium between two M forms with differing Schiff base accessibility.
Conclusions:
- The M intermediate exists in at least two forms in equilibrium, differing in Schiff base accessibility.
- Inhibitors like glutaraldehyde, LuCl3, glycerol, and sucrose stabilize the less accessible M form.
- Findings support the model of azide as a penetrating proton donor, rather than a catalytic base.