Antimycin A is added to mitochondria oxidizing NAD-linked substrates. Which pattern of redox state among the electron carriers would be observed distal to the site of blockade?

• A Cytochrome aa3 becomes fully reduced
• B Coenzyme Q pool becomes fully oxidized
• C Cytochrome c and cytochrome aa3 remain oxidized ✓
• D All carriers on both sides of the block become reduced

Explanation

Antimycin A inhibits Complex III at the Qi site, preventing reoxidation of ubiquinol. Carriers proximal to the block (the Q pool and cytochrome b) become fully reduced, while carriers distal to it, cytochrome c and cytochrome aa3, receive no electrons and remain oxidized. This proximal-reduced, distal-oxidized split is the classic way inhibitor sites were mapped spectrophotometrically.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.