Question

In a preparation of isolated mitochondria, the succinate is used as the sole substrate in the presence of ADP and Pi to stimulate the transfer of electrons and the synthesis of ATP. An inhibitor X of the respiratory chain is added. Then, we observed an accumulation of the cofactors of the respiratory chain either in oxidized form or in reduced form as indicated in the table below. Based on these results, indicate from the list below, which inhibitor is used.

Cofactors	Forms
FAD/FADH2	Reduced
Ubiquinone/Ubiquinol	Reduced
Cytochrome C	Reduced
O2/H2O	Oxidized

Inhibitors	Roles
Rotenone	Inhibits the complex I
Malonate	Inhibits the complex II
Antimycine	Inhibits the complex III
Cyanide	Inhibits the complex IV
Oligomycine	Inhibits the complex V

Answer 1

Option D, cyanide, inhibitor of complex IV

All the ETC components before complex IV will remain in reducing state while O2 and H20 ( which is reduced by complex IV) will be in oxidized state.