Pyruvate carboxylase

Pyruvate carboxylase is a biotin-dependent enzyme that uses ATP to convert pyruvate and bicarbonate into oxaloacetate. It replenishes citric-acid-cycle intermediates and supports gluconeogenesis.

Biotin: Biotin is a water-soluble vitamin that serves as a covalently bound carbon-dioxide carrier in several carboxylation reactions. It carries the carbon dioxide that pyruvate carboxylase adds to pyruvate.
Gluconeogenesis: Gluconeogenesis is the synthesis of glucose from non-carbohydrate precursors, especially in liver and kidney. Its first committed steps use oxaloacetate made by pyruvate carboxylase.
Bicarbonate: Bicarbonate is a dissolved form of inorganic carbon that serves as a carbon-dioxide source in many carboxylation reactions. It supplies the carbon atom incorporated into oxaloacetate.
Pyruvate dehydrogenase complex: The pyruvate dehydrogenase complex converts pyruvate into acetyl-CoA and carbon dioxide. It irreversibly oxidizes pyruvate, whereas pyruvate carboxylase adds carbon to it.
Carboxylation: Carboxylation is the chemical addition of a carboxyl group to a molecule. Pyruvate carboxylase performs this reaction while consuming ATP.
Citric acid cycle: The citric acid cycle is a series of reactions that oxidizes acetyl-CoA and transfers energy to electron carriers. The enzyme restores oxaloacetate and other intermediates withdrawn from this cycle.
Acetyl-CoA: Acetyl-CoA is a two-carbon metabolic intermediate that carries an acetyl group into biosynthetic and energy-producing pathways. It activates pyruvate carboxylase and signals abundant fuel availability.
Phosphoenolpyruvate carboxykinase: Phosphoenolpyruvate carboxykinase converts oxaloacetate into phosphoenolpyruvate using GTP or ATP, depending on the organism. It often follows pyruvate carboxylase in gluconeogenesis, carrying carbon toward glucose.
Oxaloacetate: Oxaloacetate is a four-carbon molecule that participates in the citric acid cycle and several metabolic pathways. It is the product formed when the enzyme carboxylates pyruvate.
Anaplerotic reactions: Anaplerotic reactions replenish intermediates consumed from metabolic cycles. Pyruvate carboxylase is a major route for refilling citric-acid-cycle intermediates.

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