Introduction
The
bc1
operates via the modified Q-cycle in which ubiquinol (UQH2) is oxidized at the Qo centre on the cytosolic side of the membrane. The two protons are released into the intermembrane space and the first electron is passed to the high potential chain consisting of an iron-sulphur centre (FeS) in the iron sulphur protein and heme
c1, and then passed to cytochrome c
(Cytc). The second electron is passed to the low potential chain consisting of heme bL
and
bH
and then used to reduce ubiquinone at the Qi centre using protons from the matrix.
The two b-hemes straddle the membrane and their oxidation state is sensitive to the membrane potential so that they are an intrinsic sensor of the membrane potential.
While the algorithm to calculate the membrane potential from the oxidation state of the hemes is complex and based on a sophisticated thermodynamic analysis, the Iberius makes measuring the membrane potential very simple.
First the Iberius cell spectroscopy system measures the oxidation state of
bH, bL
and Cytc as well as the turnover number of the
bc1
complex. Then the Iberius software implements the algorithms to calculate the membrane potential, pH gradient and redox potential of the ubiquinone pool in millivolts. The methodology and algorithms have been published [1, 2]
To achieve millivolt precision, the calculation is based on the average data over a 30 second epoch.