Similarly, QR protects against cytotoxicity by catalyzing a two electron reduction of quinones that arise from one electron reduction.
Consequently, the efficient cellular protection of IRFI005 against toxic free radicals can be explained by a two electron-transfer process, because of reduced inter-frontier molecular orbital energy gap barrier at physiological pH.
By comparison, an electron is half a million electron volts, and a proton is about 2,000 times heavier.
(By comparison, a proton is about a billion electron volts, and an electron is about half a million).
The overall HemN reaction involves a net four electron oxidation, probably involving two H-atom abstractions by dAdo followed by two one-electron oxidations.
Laccase has been used in the synthesis of bio-fuel cells due to its ability to oxidize phenols, and reduction of oxygen to water by four electron transfer at high redox potential (Zheng et al. 2008), which is an important application of laccase in the cathode compartment of bio-fuel cells (Quan et al. 2004).
To deal with rising levels of O2, a direct strategy is to reduce it by four electrons all the way to water; this process may have been catalyzed early on by the widespread cytoplasmic flavodiiron proteins, which perform this reaction with turnovers almost identical to those of the "canonical" membrane attached heme copper or cytochrome bd oxygen reductases.
When the molecule is excited (e.g., by absorption of a photon), one electron is promoted to a previously unoccupied orbital, and, if its spin does not change, then the two (now unpaired) electrons still have opposing spin and the molecule is still in a singlet state.
This is a two-level system with electron being either at the donor or at acceptor, and it is characterized by four electron-conformational states with different occupancies. .
