They had highly, highly inbred (identical) fruitflies with respect to nuclear genes. They maintained them as identical as possible. Different strains had mitochondria with minor variations in mtDNA, within normal limits, but with differences of "fit" to the (all identical) nuclear genome. Some combinations gave better ETC characteristics than others.
To see if the variations in function were due to ROS flux they treated the flies with n-acetyl-cysteine, a glutathione precursor, producing an excellent scavenger of ROS. You know:
To see if the variations in function were due to ROS flux they treated the flies with n-acetyl-cysteine, a glutathione precursor, producing an excellent scavenger of ROS. You know:
2G-SH + H2O2 -> G-S-S-G + 2H2O
and all should be well, or at least better.
That didn't work out too well. Males were more or less OK. Most females were "seedy" on NAC. In one strain all of the females, only, died. They checked glutathione levels and the NAC appeared to be doing what it was supposed to do, lots of glutathione.
Lane's idea, which is rather insightful as regards life, is that a body will tolerate an ROS flux within certain limits. To limit excessive ROS formation cells are willing to limit oxidative phosphorylation by deactivating complex I. Compromising ATP production is considered acceptable in order to limit ROS generation to "tolerable" limits.
This is not really surprising. If we think about uncoupling proteins their core function is to dissipate delta psi to a voltage which will not generate many ROS (less than ~140mV), at the cost of decreased ox-phos.
At a guess you might be able to limit/localise the glutathiolation effect to those proteins which are responsible for excess ROS, so glutathione glutathiolates the cysteines within said protein (in this example complex I) in proportion to ROS being generated. Like this
G-SH + Prot-SH + H2O2 -> G-S-S-Prot + 2H2O
Glutathiolation has evolved to alter the function of a protein in such a manner as to decrease ROS generation, even if that includes a decrease in oxidative phosphorylation.
Lane's guess is that female flies, with their high demand for ATP for egg production, couldn't cope with the drop in ox-phos mediated by glutathiolation of complex I.
These flies died in order to limit ROS production.
Have I ever mentioned that ROS are central to, well, everything?
Peter
Supplementary thought: Perhaps we could better phrase it that oral NAC raises glutathione to levels in excess of those which are already ideal, so hyper-glutathiolation causes death by excess ox-phos limitation. This would be particularly problematic for flies with slightly more ROS generation than others. The flies were okay provided ROS and glutathiolation of complex I were at physiological appropriate levels.
Fascinating in view that NAC/glutathione appears to be a pretty Good Drug in general terms. But, as always, over riding evolution has costs.
