At which site does antimycin act? A B C D a) A b) B c) C d) D A biochemist studi

Question

At which site does antimycin act?

A

B

C

D

a)

A

b)

B

c)

C

d)

D

A biochemist studies oxidative phosphorylation in mitochondria isolated from rat liver. He adds mitochondria to an airtight chamber in a medium containing excess ADP and phosphate. He places an oxygen electrode in the chamber to measure oxygen consumption. This is the experimental protocol 1. He adds a substrate to the chamber 2. He adds an inhibitor that stops oxygen consumption. 3. He takes a sample for measuring ATP 4. He adds another substrate to determine if it relieves the inhibition (i.e., starts oxygen consumption again) The substrates and inhibitors used, as well as the results, are shown in the table. The diagram shows the electron transport chain and possible sites where the inhibitors can act. H' Ht Ht NADHH NAD FAD inner membrane 2H20 ADP+ ATP toggle between examples

Explanation / Answer

Option C is Correct.

Antimycin A (AMA) is a chemical compound obtained from Streptomyces Kitazawensis. It binds to the Qi site of cytochrome c reductase in the mitochondrial electron transport chain where it inhibits the oxidation of ubiquinol and thus the flow of electrons between cytochrome b and c in the complex III.

The electron transport inhibition by antimycin causes a loss of the mitochondrial membrane potential which collapses the proton gradient across the mitochondrial inner membrane, . The consequences of inhibiting complex III cause an increase in the production of reactive oxygen species (ROS ) and a reduction in the cellular levels of ATP .

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