Taurine, Glutathione and Bioenergetics - Advances in Experimental Medicine and Biology - page 2

Abbreviations

GSH Glutathione

GSSG Oxidised glutathione

ROS Reactive oxygen species

1.1 Introduction

The chemiosmotic theory proposed by Peter Mitchell in the 1960s is today accepted
as the basis for the understanding of the oxidative phosphorylation and subsequent
ATP production in the bioenergetic processes in the mitochondria (Mitchell 1966,
1968 ; Nicholls and Ferguson 2002 ). The presentation in most biochemical text-
books focuses on the pH and the electrical gradients across the mitochondrial mem-
branes. The gradients combine to form an electrical potential D E Total for moving
protons across the inner-membrane:

RT

Δ= − E log(10) Δ pH. (1.1)

Total

F

This potential, often referred to as the proton-motive force, drives by use of pro-
ton movement the ATP production through the ATP synthase protein complex loca-
lised in the mitochondrial inner-membrane.
A series of arguments based on experimental observation can be given that the pH
in the cytosol is about 7.0-7.4, and in the mitochondrial matrix pH is most likely in
the range 7.8-8.5. In order to stabilise the ATP production, it seems evident that locali-
sation of a pH buffer in the mitochondrial matrix is necessary (Hansen et al. 2010 ) .
Furthermore, it is generally accepted that the proton-motive force can be considered
as constant about 200 mV. It is generally accepted that no appreciable dependence on
the matrix pH is observed [e.g. Fig. 4.5 in Bioenergetics 3 (Nicholls and Ferguson
2002 )]. However, such constancy of two apparently independent contributions needs
explanation from a theoretical argument (see later in Sect. 1.2.6 and Fig. 1.1 ).

1.2 Mitochondria: pH and Redox Buffering

1.2.1 Taurine: pH Buffer

Taurine has previously (Hansen et al. 2006, 2010 ) been presented as a compound
that possesses the optimal characteristics to be a pH buffer in the mitochondrial
matrix. Taurine is found ubiquitously in animal tissue with concentrations in the
millimolar range. Notably high concentrations of taurine in oxidative tissue lead to