Question

For each of the following TCA Cycle enzymes, list the name of the enzyme in the fatty

      acid b-oxidation pathway that is most similar in function and state why.

1. Succinate dehydrogenase

2. Fumarase                                           

3. Malate dehydrogenase                       

4. Aconitase

Answer 1

1. the enzyme acyl CoA dehydrogenase of the beta oxidation pathway is similar to that of succinate dehydrogenase.

in both cases there these enzymes drive oxidation of substrates to productss. The succinate dehydrogenase oxidises succinate to fumarase while acyl CoA dehydrogenase oxidises acyl CoA to trans-Δ2-enoyl-CoA.

2. the enzyme enoyl CoA hydratase is similar to that of Fumarase as both involves hydration of their sustrate molecule to form the product.

Fumarase hydrates fumarate to malate and enoyl CoA hydratase hydrates trans-Δ2-enoyl-CoA to  form L-3-hydroxyacyl CoA.

3.the enzyme 3-hydroxy acyl CoA dehydrogenase is similar to that of malate dehydrogenase, as both catalyses reactions involving oxidation by using NAD+ to NADH.

while malate dehydrogenase form oxaloacetate from malate , the 3-hydroxy acyl CoA dehydrogenase enzyme form β-ketoacyl CoA from L-3-hydroxyacyl CoA. both by using NAD+.

4. The propionyl CoA enzyme is related to the aconitase enzyme.

The propionyl CoA enzyme catalyses a stereoisomeric reaction to form methyl malonyl CoA from propionyl CoA (this reaction takes place in the fatty acids having odd number of carbons and thus producing propionyl CoA) which then undergoes a lot of rearrangement to form succinyl CoA.

aconitase also catalyses a similar stereospecific isomerization of citrate to isocitrate in the TCA cycle.