Generally, increasingly in the menaquinone potential increased the thermionic efficiency of the system with respect to membrane potential. To obtain high menaquinone potential modifying other recognized internal parameters such as cytochrome C potential and temperature are required .
Higher \(V_{MQ}\) values would require higher \(V_{MtrC}\) values so that electrons can reduce menaquinone from the cytochromes in the cell membrane, which meant that incoming electrons have to arrive at a higher potential.
Figures 3B, C show the various \(V_{MtrC}\) values and how the thermionic efficiency changes with those changes in \(V_{MQ}\). The general trend seen is that the efficiency rises with more negative \(V_{MQ}\), but the higher \(V_{MtrC}\) reduces efficiency given the same \(V_{MQ}\). Thus, there is a balance that is required between increasing either \(V_{MtrC}\) or \(V_{MQ}\).
To describe how increased MQ potential could improve the thermionic efficiency, the effect of menaquinone potential (\(V_{MQ}\)) on the EET system movement in protons across the membrane was investigated (figure 3D). By raising the \(f_{uphill}\) the menaquinone potential shifts in its position between \(V_{NADH}\) and \(V_{O_2}\), which causes more NADH reduction and then increasing the thermionic efficiency. Also, proton movement at MQ standard potential is shown in figure 3E. The increase in proton limits, where increasing the proton limits favour thermionic efficiencies particularly at lower membrane potentials is seen.
2.1.3- Temperature
Figure 3F, G investigates the temperature effect on the efficiency of the system at various menaquinone potential with and without proton limitation, respectively. limits in proton movements (5 per electron) are introduced in Figure 3F, unsurprisingly at lower temperatures (hence lower membrane potentials), we get a reduced thermionic efficiency. Any increases seen in both the \(V_{MQ}\)at standard and at the lower potential were accompanied by a roughly 1.4% change in efficiency at around 302K and 326K respectively. For the lower potential, staying at room temperature offers the maximum efficiency, while at the standard potential, the rise in efficiency occurs at around 326K.
In the case of no proton movement limitation, at -35mV of \(V_{MQ}\) there is a rise in temperature. However, at more favorable menaquinone potentials this is not the case. Hence any temperature dependence is dependent on how the membrane potential affects the overall thermionic efficiency.