Question

A researcher follows a protocol to test the activity of a mitochondrial extract containing all of the soluble enzymes of the matrix. Because the mitochondrial extract was dialyzed, the protocol lists low molecular weight cofactors that must be added to the extract in order to catalyze the oxidation of acetyl-CoA to CO2. The list does not include lipoic acid, a known cofactor of the citric acid cycle. Why is lipoic acid omitted from the list of cofactors to add back to the extract? O O O O O The added TPP can substitute for lipoic acid in the pyruvate dehydrogenase complex. Lipoic acid is covalently attached to the pyruvate dehydrogenase complex. The disulfide bond in lipoic acid prevents diffusion through the dialysis membrane. The Kd of lipoic acid binding to pyruvate dehydrogenase is extremely low. The oxidation of acetyl-CoA to CO2 does not require lipoic acid in vitro.

Answer 1

The answer is: Lipoic acid is covalently attached to the pyruvate dehydrogenase complex

Step-by-step explanation:

It can be said that via a convalent amide bond lipoic acid binds to the terminal lysine residue found in the lipophilic domains of the enzyme. The importance of lipoic acid is that it acts as a cofactor in the pyruvate dehydrogenase enzyme complex.

Answer 2

Lipoic acid is covalently attached to the pyruvate dehydrogenase complex.

Step-by-step explanation:

The pyruvate dehydrogenase complex has lipoic acid bound covalently to it.

This explain why dialysis is not effective in separating the lipoic acid from the enzyme