In the citrate cycle, oxaloacetate is formed from malate. Oxaloacetate is then used as the starting substrate in another round of the citrate cycle. But oxaloacetate is also a precursor for many other molecules. Which of the following is NOT a potential fate of the molecule oxaloacetate?

A. aspartate

B. citrate

C. phosphoenolpyruvate

D. heme cofactors

D. heme cofactors

Explanation:

A principal route by which Oxaloacetate formed is upon oxidation of L-malate, catalysed by malate dehydrogenase, in the citric acid cycle.

Oxaloacetate can also be precusors in several ways.

Oxaloacetate can also arise from transamination or deamination of aspartic acid to form aspartate.

Citrate can be formed from the reaction of Oxaloacetate in the presence of acetyl-coA and water. This reaction is is catalyzed by citrate synthase.

It can arises from the condensation of pyruvate with carbonic acid, driven by the hydrolysis of ATP:

CH3C (O) CO2 - + HCO3 - + ATP → - O2CCH2C (O) CO2 - + ADP + Pi

Occurring in the mesophyll of plants, this process proceeds via phosphoenolpyruvate, catalysed by pyruvate carboxylase.

A cofactor is a non-protein chemical compound that is required for the protein's biological activity. There are types of co factors

Organic Cofactors, such as flavin or hemecofactor, and

inorganic cofactors, such as the metal ions e. g Mg2+.

We can then conclude that heme cofactors in not a potential fate of the molecule oxaloacetate.