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Title: The Chloroplast Tat Pathway Transports Substrates in the Dark

Abstract

Photosynthetic electron transport pumps protons into the thylakoid lumen, creating an electrochemical potential called the protonmotive force (PMF). The energy of the thylakoid PMF is utilized by such machinery as the chloroplast F0F1-ATPase as well as the chloroplast Tat (cpTat) pathway (a protein transporter) to do work. The bulk phase thylakoid PMF decays rapidly after the termination of actinic illumination, and it has been well established via potentiometric measurements that there is no detectable electrical or chemical potential in the thylakoid after a brief time in the dark. Yet, we report herein that cpTat transport can occur for long periods in the dark. We show that the thylakoid PMF is actually present long after actinic illumination of the thylakoids ceases and that this energy is present in physiologically useful quantities. Consistent with previous studies, the dark-persisting thylakoid potential is not detectable by established indicators. In conclusion, we propose that cpTat transport in the dark is dependent on a pool of protons in the thylakoid held out of equilibrium with those in the bulk aqueous phase.

Authors:
 [1];  [2]
  1. Univ. of California, Davis, CA (United States); Univ. of Manchester, Manchester (United Kingdom)
  2. Univ. of California, Davis, CA (United States)
Publication Date:
Research Org.:
Univ. of California, Davis, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22). Chemical Sciences, Geosciences & Biosciences Division
OSTI Identifier:
1490447
Grant/Contract Number:  
FG02-03ER15405
Resource Type:
Accepted Manuscript
Journal Name:
Journal of Biological Chemistry
Additional Journal Information:
Journal Volume: 283; Journal Issue: 14; Journal ID: ISSN 0021-9258
Publisher:
American Society for Biochemistry and Molecular Biology
Country of Publication:
United States
Language:
English
Subject:
59 BASIC BIOLOGICAL SCIENCES

Citation Formats

Braun, Nikolai A., and Theg, Steven M. The Chloroplast Tat Pathway Transports Substrates in the Dark. United States: N. p., 2008. Web. doi:10.1074/jbc.M708948200.
Braun, Nikolai A., & Theg, Steven M. The Chloroplast Tat Pathway Transports Substrates in the Dark. United States. doi:10.1074/jbc.M708948200.
Braun, Nikolai A., and Theg, Steven M. Wed . "The Chloroplast Tat Pathway Transports Substrates in the Dark". United States. doi:10.1074/jbc.M708948200. https://www.osti.gov/servlets/purl/1490447.
@article{osti_1490447,
title = {The Chloroplast Tat Pathway Transports Substrates in the Dark},
author = {Braun, Nikolai A. and Theg, Steven M.},
abstractNote = {Photosynthetic electron transport pumps protons into the thylakoid lumen, creating an electrochemical potential called the protonmotive force (PMF). The energy of the thylakoid PMF is utilized by such machinery as the chloroplast F0F1-ATPase as well as the chloroplast Tat (cpTat) pathway (a protein transporter) to do work. The bulk phase thylakoid PMF decays rapidly after the termination of actinic illumination, and it has been well established via potentiometric measurements that there is no detectable electrical or chemical potential in the thylakoid after a brief time in the dark. Yet, we report herein that cpTat transport can occur for long periods in the dark. We show that the thylakoid PMF is actually present long after actinic illumination of the thylakoids ceases and that this energy is present in physiologically useful quantities. Consistent with previous studies, the dark-persisting thylakoid potential is not detectable by established indicators. In conclusion, we propose that cpTat transport in the dark is dependent on a pool of protons in the thylakoid held out of equilibrium with those in the bulk aqueous phase.},
doi = {10.1074/jbc.M708948200},
journal = {Journal of Biological Chemistry},
number = 14,
volume = 283,
place = {United States},
year = {2008},
month = {1}
}

Journal Article:
Free Publicly Available Full Text
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Citation Metrics:
Cited by: 11 works
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Figures / Tables:

Figure 1 Figure 1: Transport of a cpTat substrate in the dark is sensitive to nigericin and valinomycin. Thylakoids were pre-illuminated for 3 min and then kept on ice in darkness for 10 min before the first transport reaction was initiated; time = -10 corresponds to the moment the pre-illumination light wasmore » extinguished. iOE17 transport was initiated at 10-min intervals, and the reactions were each of 5-min duration. A, control reactions without the addition of nigericin and valinomycin. mOE17, mature OE17. B, reactions in which 1 μM both nigericin and valinomycin (nig/val) were added just before initiation of the transport reactions. The first lanes in A and B were loaded with 10% of the iOE17 translation product added to the transport reactions. C, normalized means ±S.E. from three time course experiments for untreated control samples (circles) and samples treated with 1 μM both nigericin and valinomycin just before initiation of the transport reaction (diamonds). An exponential regression line is drawn through the control points. The transport of iOE17 was calculated by comparing the densities of the mature bands to those of the 10% load lanes.« less

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