Question

Vitamin C can bypass complexes 1 and 3 to directly reduce 2 cytochrome c proteins. What is the P:O ratio for vitamin C? Explain

Answer 1

P:O ratio is defined as the ratio of organically bound phosphorous produced per mole of oxygen. It is taken as a measure of oxidative phosphorylation.

When Vitamin C is oxidised (or when it reduces Cytochrome C), only 1 ATP is formed, Hence, Vitamin C has P:O ratio of 1.

It reduces the Cytochrome C through a dye called as N,N,N',N'-Tetramethyl-Para-Phenylendiamine (TMPD) thus bypassing the complexes 1 and 3 which makes it P:O ratio=1

NADH
1
NADH-Q Oxidoreductase
2
Q<-----FADH2<-----Succinate
3
Cytochrome c1
4
Cytochrome c<----Vitamin C + TMPD (Non physiological) Production of 1 ATP molecule
5
Cytochrome oxidase
6
Oxygen (O2)

Rotenone, Amytal blocks at position 2 (mentioned above) and antimycin A block at position 4. Both of which can be bypassed by Vitamin C. On the other hand, Cyanides, Azides, Carbon monoxide block at position 6 and hence cannot be bypassed explaining their toxic characters when compared to other blockers (poisons) of Electron transport