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Proton Transfer and Protein Conformation Dynamics in Photosensitive Proteins by Time-resolved Step-scan Fourier-transform Infrared Spectroscopy
Published on: June 27, 2014
Cooperativity-regulated parallel pathways of the bacteriorhodopsin photocycle
1Institute of Biophysics, Hungarian Academy of Sciences, Szeged.
FEBS Letters
|January 3, 1995
Summary
This study reveals a model for the bacteriorhodopsin (BR) photocycle, detailing parallel pathways and cooperative interactions. The findings clarify intermediate decay kinetics and offer a new method for kinetic evaluation.
Area of Science:
- Biophysics
- Photochemistry
Background:
- Bacteriorhodopsin (BR) is a light-driven proton pump with a complex photocycle involving multiple intermediates.
- Previous studies using double flash experiments proposed a model for the BR photocycle.
Purpose of the Study:
- To investigate the millisecond part of the bacteriorhodopsin photocycle at high pH using actinic light density dependence.
- To validate and refine the existing model of the BR photocycle, including its intermediate sequences and decay kinetics.
Main Methods:
- Analysis of the actinic light density dependence of the millisecond phase of the BR photocycle at high pH.
- Kinetic evaluation and comparison of different pathways and intermediate decay rates.
Main Results:
- The study confirms a model comprising parallel pathways (Mf-->N-->BR and M(s)-->BR) regulated by cooperative BR molecule interactions.
- The decay of M(s) is slower than Mf, involving direct Schiff-base reprotonation and near-simultaneous ground-state recovery.
- M(s) decomposes into M'f and M's, with M'f preceding a conformational change before Mf decay. The amount of intermediate N decreases with increasing fraction cycling, while its decay rate remains independent.
Conclusions:
- The findings support a refined model of the bacteriorhodopsin photocycle, consistent with previous double flash experiments.
- The research elucidates the kinetics of intermediate decay and suggests a novel approach for kinetic evaluation under specific conditions.
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