Taurine, Glutathione and Bioenergetics - Advances in Experimental Medicine and Biology - page 6

Table 1.2 Approximate actual redox point potentials E actual,pH (mV) at different pH values

Typical ox/red
ratio Redox pair pH = 7.0 pH = 7.5 pH = 8.0 pH = 8.5

NADH/NAD + 10 −290 −305 −320 −335

NADPH/NADP + 0.01 −380 −395 −410 −425

GSH/GSSG(when
10 mM)

0.01 −240 −270 −300 −330

Based directly on the values given in Table 3.2 in Bioenergetics 3 (Nicholls and Ferguson 2002 ) .
In their calculations the factor 2.303 RT/F from the Nernst equation was set to 60 mV (correspond-
ing to T = 302 K or 29.2°C)

Fig. 1.2 Estimation of actual redox potentials E actual,pH (mV) for the redox pairs NADH/NAD + ,
NADPH/NADP + , and GSH/GSSG at pH = 7.0 and pH = 8.5, respectively. The concentrations of the
compounds are based on the values given in Table 3.2 in Bioenergetics 3 (Nicholls and Ferguson
2002 ). At the slightly alkaline pH = 8.5, it is possible to obtain redox equilibrium between NADH/
NAD + and GSH/GSSG

and the GSH/GSSG redox pairs become almost identical. That is in the pH range of
8.0-8.5, where taurine acts as a pH buffer, it is possible to obtain thermodynamic
equilibrium between the NADH/NAD + and GSH/GSSG, whereas NADPH/NADP +
acts as a sort of cofactor for the involved enzymes! Consequently, taurine can sud-
denly be given a very important supporting role to GSH in the mitochondrial matrix.
In a recent advanced theoretical and numerical calculation model for mitochon-
drial energetics only the NADH/NAD + -redox couple was included (Wei et al. 2011 ) ,
although the GSH/GSSG was included in a previous unifying hypothesis focusing
on reactive oxygen species (ROS) and oxidative stress (Aon et al. 2010 ) . Now, it
seems that taurine also should be included in such calculation models due to its
contribution to the mitochondrial pH buffering capacity.