vate carboxylase (EC 6.4.1.1) catalyzes the carboxylation of pyruvate to form ox

Question

vate carboxylase (EC 6.4.1.1) catalyzes the carboxylation of pyruvate to form oxaloacetate, anMap intermediate in several metabolic pathways. Complete parts (a), (b) and (c) beiow. The net reaction is pyruvate+ CO,+ATP+H,0 oxaloacetate+ ADP+P,+2H (a) What is the role of ATP in this reaction? O It activates CO2 (HCo3). O It is the source of the phosphory group in the product. O It allosterically activates the enzyme. O It activates the enzyme cofactor. (b) Identify the atom on the cofactor that acts as a nucleophile and reacts with the carbon dioxide Click on the atom to highlight it. The selected atom will be highlighted green. (H atoms are not graded.) NH The name of the cofactor is (Select answer continued below.. (c) Identify the allosteric activator of pyruvate carboxylase ATP

Explanation / Answer

a. In the conversion of pyruvate into oxaloacetate, ATP is involved as a source of phosphoryl group. ATP is converted to ADP and inorganic phosphate.

c. A high level of acetyl-CoA inside mitochondria is required for optimal activity of pyruvate carboxylase. Acetyl-CoA serves as an allosteric activator of this enzyme, even though acetyl-CoA itself does not partake in the reaction. The mitochondrial level of acetyl-CoA starts to rise when fatty acids are broken down to fill a demand for energy, and this rise causes pyruvate carboxylase to replenish the TCA cycle (by generating OAA from pyruvate), so that acetyl-CoA can be combusted through citrate formation.

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