Light-induced currents from oriented purple membrane
Liu, Su-Yi
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Permalink
https://hdl.handle.net/2142/20356
Description
Title
Light-induced currents from oriented purple membrane
Author(s)
Liu, Su-Yi
Issue Date
1990
Doctoral Committee Chair(s)
Ebrey, Thomas G.
Department of Study
Biophysics and Computational Biology
Discipline
Biophysics
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biophysics, General
Language
eng
Abstract
This thesis is a report on photocurrent measurements of purple membrane oriented in an polyacrylamide gel. In the first section, the photocurrent measuring system was frequency analyzed from DC to 100 MHz. The optimized conditions that can measure the photocurrent signal in the 70 ms to 32 ns range without any distortion were found. In the second section, the correlation of the microsecond photocurrent component with the optical intermediates of the photocycle of bacteriorhodopsin was studied. It was found that the rise phase of microsecond component of photocurrent is closely correlated with K-L optical transition and decay phase is closely correlated with L-M transition when the salt concentration is relatively high. This correlation holds through the entire pH range that the L-M transition can be observed and is not temperature dependent. In the third section, the effect of salt on the microsecond photocurrent component was studied. In the fourth section, the effect of pH buffers on the microsecond photocurrent component was studied. Through these studies, it was concluded that: (1) when the salt (or pH buffer) concentration is relatively high, the microsecond component represents a proton release signal; (2) when the salt (or buffer) concentration is relatively low, the microsecond photocurrent component represents a sum of proton release and metallic cations (or protonated pH buffer molecules) moving backwards in the direction opposite to that of the proton release. A counter current theory for the photocurrent was developed. Many characteristics of the proton pump of bacteriorhodopsin, which are difficult to study by other methods, were studied using the photocurrent measurement method.
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