In the reoxidation of QH2 by purified ubiquinone-cytochrome c reductase (Complex III) from heart muscle, the overall stoichiometry of the reaction requires 2 mol of cytochrome c per mole of QH2 because:

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a. cytochrome c is a one-electron acceptor, whereas QH2 is a two-electron donor.

b. cytochrome c is a two-electron acceptor, whereas QH2 is a one-electron donor.

c. cytochrome c is water soluble and operates between the inner and outer mitochondrial membranes

d. heart muscle has a high rate of oxidative metabolism, and therefore requires twice as much cytochrome c as QH2 for electron transfer to proceed normally.

e. two molecules of cytochrome c must first combine physically before they are catalytically active.

cytochrome c is a one-electron acceptor, whereas QH2 is a two-electron donor. ( A )

Explanation:

The overall stoichiometry of the reaction requires 2 mol of cytochrome per mole of QH2 because a cytochrome is simply a one-electron acceptor while QH2 is not a one-electron donor ( i.e. it is a two-electron donor )

An electron donor in a reaction is considered a reducing agent because it donates its electrons to another compound thereby self oxidizing itself in the process.