Monday 22 October 2007
Pyruvic acid (CH3COCO2H) is an alpha-keto acid. Pyruvate plays an important role in biochemical processes. The carboxylate anion of pyruvic acid is known as pyruvate.
Pyruvate is the output of the aerobic metabolism of glucose known as glycolysis. One molecule of glucose breaks down into two molecules of pyruvate, which are then used to provide further energy, in one of two ways.
Pyruvate is converted into acetyl-coenzyme A.
Pyruvate is also converted to oxaloacetate by an anaplerotic reaction which replenishes Krebs cycle intermediates; alternatively, the oxaloacetate is used for gluconeogenesis.
If insufficient oxygen is available, the acid is broken down anaerobically, creating lactic acid in animals and ethanol in plants.
Pyruvate from glycolysis is converted by anaerobic respiration to lactate using the enzyme lactate dehydrogenase and the coenzyme NADH in lactate fermentation, or to acetaldehyde and then to ethanol in alcoholic fermentation.
Pyruvate is a key intersection in the network of metabolic pathways. It unites several key metabolic processes.
Pyruvate can be converted :
to carbohydrates via gluconeogenesis
to fatty acids or energy through acetyl-CoA
to the amino acid alanine
Pyruvate production by glycolysis
Pyruvate decarboxylation to acetyl CoA
Pyruvate carboxylation to oxaloacetate
Transamination by the alanine aminotransferase
Reduction to lactate
Citric acid cycle (or Krebs cycle or TCA cycle)
The citric acid cycle (or Krebs cycle or TCA cycle) takes place within the mitochondrial matrix. In this cycle, pyruvic acid generated from glycolysis is converted into acetyl coenzyme A (acetyl CoA) by losing a carbon dioxide molecule. It then combines with oxaloacetic acid to form citric acid, a six-carbon molecule.
In total, it loses 2 CO2 molecules and 4 electrons, of which 3 are accepted by NAD+ to reduce it to NADH, and the last electron accepted by FAD+ to reduce to FADH2 in redox reactions.
In the end, it regenerates oxaloacetic acid to continue the citric acid cycle. In addition, a single GTP molecule is created from the combination of GDP and a phosphate group.
Since 2 pyruvic acid molecules are formed by glycolysis, each time a cell undergoes glycolysis two turns of the citric acid cycle will occur. That means that the citric acid cycle produces a total of 6 NADH, 2 FADH2, and 2 GTP molecules.
Pathology of pyruvate metabolism and transport
pyruvate dehydrogenase deficiency
SLC16A1 (MCT1) transporter in exercise-induced hypoglycemia and erythrocyte lactate transporter defect (MIM.245340)