So far, we have considered the different sites for hydrogen peroxide production,
and now we're going to look into how
mitochondria can actually control hydrogen peroxide release.
One of the most important features of cell signals is that the signal,
or secondary molecule, must be controlled.
This can be achieved through its degradation,
and in the case of hydrogen peroxide,
this is done through antioxidant systems.
Secondary signalling of molecule availability is also controlled through its production.
Again, I will use the example of cyclic AMP,
where its production is tightly modulated by the activation of adenylyl cyclase.
Much like cyclic AMP,
hydrogen peroxide production also needs to be tightly controlled to
ensure proper fulfilment of its secondary signalling properties.
Controlling hydrogen peroxide production by mitochondria started
originally with the identification of systems that can prevent oxidative distress.
Proton leaks to this end,
are the most well characterised, and most disputed system,
for controlling mitochondrial hydrogen peroxide production.
This is achieved through the induction of proton return to the matrix,
which alters membrane potential,
an important factor in mitochondrial ROS production.
Another important mechanism for controlling
hydrogen peroxide production is the assembly and disassembly of super complexes,
which can affect electron transfer efficiency,
and how much ROS is formed by the respiratory chain.
The third and final mechanism which I'll focus on the most,
is redox signals, and the oxidation of cysteine switches.
This mechanism is important since the oxidation of protein switches is
mediated by changes in the overall hydrogen peroxide buffering capacity of the matrix,
and the redox state of the glutathione system.
In particular, S-glutathionylation reactions seem to play
an integral role in regulating mitochondrial ROS production.