TU Darmstadt / ULB / TUbiblio

Electrophysiological analysis of the yeast V-type proton pump: variable coupling ratio and proton shunt.

Kettner, C. and Bertl, A. and Obermeyer, G. and Slayman, C. L. and Bihler, H. (2003):
Electrophysiological analysis of the yeast V-type proton pump: variable coupling ratio and proton shunt.
In: Biophysical journal, pp. 3730-3738, 85, (6), ISSN 0006-3495, [Online-Edition: http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B94R...],
[Article]

Abstract

Isolated vacuoles from the yeast Saccharomyces cerevisiae were examined in the whole-vacuole mode of patch recording, to get a detailed functional description of the vacuolar proton pump, the V-ATPase. Functioning of the V-ATPase was characterized by its current-voltage (I-V) relationship, obtained for various levels of vacuolar and cytosolic pH. I-V curves for the V-ATPase were computed as the difference between I-V curves obtained with the pump switched on (ATP, ADP, and Pi present) or off (no ATP). These difference current-voltage relationships usually crossed the voltage axis within the experimental range (from -80 to +80 mV), thus measuring the reversal voltage (ER) for the V-ATPase, which could be compared with the standing ion gradients and free energy of ATP hydrolysis, to calculate the apparent pump stoichiometry or coupling ratio: the number of protons transported for each ATP molecule hydrolyzed. This ratio was found to depend strongly upon the pH difference (DeltapH) across the vacuolar membrane, being approximately 2H+/ATP at high DeltapH (4 pH units) and increasing to >4H+/ATP for small or zero DeltapH. That result is in quantitative agreement with previous determinations on plant vacuoles. Considerations of purely electrical behavior, together with the physical properties of a recent detailed structural model for V-ATPases, led to a linear equivalent circuit--which quantitatively accounts for all observations of variable coupling ratios in fungal and plant V-ATPases by variations of the conductance for bona fide proton pumping (GP) through the ATPase relative to independent proton shunting (GS) through the same protein.

Item Type: Article
Erschienen: 2003
Creators: Kettner, C. and Bertl, A. and Obermeyer, G. and Slayman, C. L. and Bihler, H.
Title: Electrophysiological analysis of the yeast V-type proton pump: variable coupling ratio and proton shunt.
Language: English
Abstract:

Isolated vacuoles from the yeast Saccharomyces cerevisiae were examined in the whole-vacuole mode of patch recording, to get a detailed functional description of the vacuolar proton pump, the V-ATPase. Functioning of the V-ATPase was characterized by its current-voltage (I-V) relationship, obtained for various levels of vacuolar and cytosolic pH. I-V curves for the V-ATPase were computed as the difference between I-V curves obtained with the pump switched on (ATP, ADP, and Pi present) or off (no ATP). These difference current-voltage relationships usually crossed the voltage axis within the experimental range (from -80 to +80 mV), thus measuring the reversal voltage (ER) for the V-ATPase, which could be compared with the standing ion gradients and free energy of ATP hydrolysis, to calculate the apparent pump stoichiometry or coupling ratio: the number of protons transported for each ATP molecule hydrolyzed. This ratio was found to depend strongly upon the pH difference (DeltapH) across the vacuolar membrane, being approximately 2H+/ATP at high DeltapH (4 pH units) and increasing to >4H+/ATP for small or zero DeltapH. That result is in quantitative agreement with previous determinations on plant vacuoles. Considerations of purely electrical behavior, together with the physical properties of a recent detailed structural model for V-ATPases, led to a linear equivalent circuit--which quantitatively accounts for all observations of variable coupling ratios in fungal and plant V-ATPases by variations of the conductance for bona fide proton pumping (GP) through the ATPase relative to independent proton shunting (GS) through the same protein.

Journal or Publication Title: Biophysical journal
Volume: 85
Number: 6
Divisions: 10 Department of Biology
?? fb10_botanik ??
10 Department of Biology > Yeast Membrane Biology
Date Deposited: 29 Nov 2010 15:25
Official URL: http://www.sciencedirect.com/science?_ob=MImg&_imagekey=B94R...
Identification Number: doi:10.1016/S0006-3495(03)74789-4
Export:

Optionen (nur für Redakteure)

View Item View Item