Protons: Back to N-1a and a nice quote

Eureka moment when I tripped over this gem by Vinogradov

"The redox potential of one binuclear [FeS] center (N-1a) is so negative that it can not be reduced by NADH"

Couple this with this group's conclusion:

"These results lead us to propose a model of thermodynamic control of mitochondrial ROS production which suggests that the ROS-generating site of complex I is the Fe-S centre N-1a".

You can't reduce N-1a to generate superoxide using NADH at "normal" concnetrations. The easiest way you can generate superoxide at N-1a is by reverse electron flow through complex 1 under conditions of a strong membrane potential and a high FADH2 input, in this case using succinate. Very satisfying. They also point out that, if you can get the NAD+/NADH ratio high enough you can get it far enough from its electrical mid point to pass electrons "down gradient" to N-1a. At ratios of less than about 3 parts NADH to one part NAD+ the transfer is uphill and isn't going to happen. As they say:

"...the reduction of the *ROS site [they consider that it is probably N-1a] is regulated by the NADH/NAD+ ratio rather than the NADH level (eqns 7 and 8)..."

which sort of takes us back to B3 and some cancer cells which have probably lost N-1a so fail to develop insulin resistance, ie they don't limit their energy generation to their needs. They also develop metastatic aggressiveness in proportion to their elevated NADH:NAD+ ratio (even if they expressed it as a reduced NAD+/NADH ratio!). I wrote that post a while ago, time to check it and hit publish...

Peter

BTW Vinogradov pointed out in his review paper that very few labs have the massively expensive and complex gear to look at this sort of redox research and both of the papers discussed here are from groups who know each other, Vinogradov being thanked for reading through the manuscript of the second paper. But I think they are correct.