Which enzyme catalyzes the conversion of pyruvate to oxaloacetate in gluconeogenesis?

Which enzyme catalyzes the conversion of pyruvate to oxaloacetate in gluconeogenesis?

• A. Pyruvate carboxylase
• B. Pyruvate dehydrogenase
• C. Lactate dehydrogenase
• D. Pyruvate kinase

Answer: (A)

In gluconeogenesis, the first crucial move to use a pyruvate carbon skeleton for glucose is to attach a CO2 group to pyruvate, forming oxaloacetate. This carboxylation step is carried out by pyruvate carboxylase, which sits in the mitochondria and uses ATP (and biotin) to add the carboxyl group. This activation is necessary because it creates a four-carbon compound that can be rearranged and eventually converted into phosphoenolpyruvate for glucose synthesis. From there, oxaloacetate is transported to the cytosol and converted to phosphoenolpyruvate by PEP carboxykinase, continuing gluconeogenesis. The other enzymes listed do different things: pyruvate dehydrogenase converts pyruvate to acetyl-CoA for the TCA cycle; lactate dehydrogenase reduces pyruvate to lactate; pyruvate kinase is the glycolytic enzyme that converts phosphoenolpyruvate to pyruvate, not the reverse step needed in gluconeogenesis.

In gluconeogenesis, the first crucial move to use a pyruvate carbon skeleton for glucose is to attach a CO2 group to pyruvate, forming oxaloacetate. This carboxylation step is carried out by pyruvate carboxylase, which sits in the mitochondria and uses ATP (and biotin) to add the carboxyl group. This activation is necessary because it creates a four-carbon compound that can be rearranged and eventually converted into phosphoenolpyruvate for glucose synthesis. From there, oxaloacetate is transported to the cytosol and converted to phosphoenolpyruvate by PEP carboxykinase, continuing gluconeogenesis. The other enzymes listed do different things: pyruvate dehydrogenase converts pyruvate to acetyl-CoA for the TCA cycle; lactate dehydrogenase reduces pyruvate to lactate; pyruvate kinase is the glycolytic enzyme that converts phosphoenolpyruvate to pyruvate, not the reverse step needed in gluconeogenesis.