Question

You do an experiment in which you use acetyl-CoA with 14C label on both carbons of the acetyl group. You let this run through one round of the citric acid cycle with unlabeled oxaloacetate, and monitor the production of 14CO2. At which reactions (labeled by the enzyme that catalyzes them) do you expect to detect 4CO2?a) alpha ketoglutarate dehydrogenaseb) succinyl CoA synthetasec) No reactions will yield thisd) aconitase

Answer 1

Answer: Option A - alpha ketoglutarate dehydrogenase

Explanation:

One of the peculiarities of the Citric acid cycle is that it contains two successive decarboxylation steps.

The 1st decarboxylation step is catalyzed by Isocitrate dehydrogenase, while the 2nd step is catalyzed by Alpha ketoglutarate dehydrogenase.

So, the reaction where 4CO2 is observed will be:

Oxidative decarboxylation of α-ketoglutarate to Succinyl-CoA