The pyruvate dehydrogenase is allosterically inhibited by all of the following except?

a) low adp/atp ratios

b) low amp / atp ratios

c) low nad+ / nadh ratios

d) low coa-sh / acetyl-coa ratios

e) low acetyl coa / coa-sh ratios

The correct answer is option e) "low acetyl coa / coa-sh ratios".

Explanation:

Allosteric inhibition, also known as negative allosteric modulation, occurs when a ligand decreases one enzyme's affinity to its substrate by binding to a site different from the active site. One classic example of allosteric inhibition takes place in pyruvate dehydrogenase, an enzyme that converts pyruvate into acetyl-CoA by a process called pyruvate decarboxylation. Pyruvate dehydrogenase is inhibited by the end products of the reactions that it catalyzes to regulate its activity. Therefore, a low acetyl coa / coa-sh ratios would not inhibited pyruvate dehydrogenase, on the contrary, a high concentration of acetyl coa would inhibit its activity.

e) low acetyl-CoA/CoA-sh ratios

Explanation:

The enzyme pyruvate dehydrogenase is allosterically inhibited by a high concentration of some of the products of the reaction it catalyzes: NADH and Acetyl-CoA, and ATP (since its a enzyme involved in the cellular respiration, a metabolic process that converts organic molecules into energy/ATP).

So, if you have a low ratio of acetyl-CoA/CoA-sh it means you have a more of CoA-sh than acetyl-CoA, therefore wouldn't allosterically inhibited the enzyme.