pyruvate

Examples of pyruvate in the following topics:

• Pyruvic Acid and Metabolism

  • Pyruvic acid (CH3COCOOH) is an organic acid, a ketone, and the simplest of the alpha-keto acids.
  • Pyruvic acid (CH3COCOOH; is an organic acid, a ketone, and the simplest of the alpha-keto acids.
  • The carboxylate (COO−) anion of pyruvic acid.
  • Pyruvate is an important chemical compound in biochemistry.
  • Pyruvate is a key intersection in the network of metabolic pathways.

• Breakdown of Pyruvate

  • After glycolysis, pyruvate is converted into acetyl CoA in order to enter the citric acid cycle.
  • In order for pyruvate, the product of glycolysis, to enter the next pathway, it must undergo several changes to become acetyl Coenzyme A (acetyl CoA).
  • The conversion of pyruvate to acetyl CoA is a three-step process .
  • A carboxyl group is removed from pyruvate, releasing a molecule of carbon dioxide into the surrounding medium.
  • Each pyruvate molecule loses a carboxylic group in the form of carbon dioxide.

• Outcomes of Glycolysis

  • One glucose molecule produces four ATP, two NADH, and two pyruvate molecules during glycolysis.
  • Glycolysis starts with one molecule of glucose and ends with two pyruvate (pyruvic acid) molecules, a total of four ATP molecules, and two molecules of NADH .
  • If the cell cannot catabolize the pyruvate molecules further (via the citric acid cycle or Krebs cycle), it will harvest only two ATP molecules from one molecule of glucose.
  • Additionally, the last step in glycolysis will not occur if pyruvate kinase, the enzyme that catalyzes the formation of pyruvate, is not available in sufficient quantities.
  • Thus, pyruvate kinase is a rate-limiting enzyme for glycolysis.

• Fermentation Without Substrate-Level Phosphorylation

  • During fermentation, pyruvate is metabolised to various compounds.
  • Homolactic fermentation is the production of lactic acid from pyruvate; alcoholic fermentation is the conversion of pyruvate into ethanol and carbon dioxide; and heterolactic fermentation is the production of lactic acid as well as other acids and alcohols.
  • Pyruvic acid can be made from glucose through glycolysis, converted back to carbohydrates (such as glucose) via gluconeogenesis, or to fatty acids through acetyl-CoA.
  • Pyruvic acid supplies energy to living cells through the citric acid cycle (also known as the Krebs cycle) when oxygen is present (aerobic respiration), and alternatively ferments to produce lactic acid when oxygen is lacking (fermentation).

• The Entner–Doudoroff Pathway

  • The Entner–Doudoroff pathway is an alternate series of reactions that catabolize glucose to pyruvate.
  • The Entner–Doudoroff pathway describes an alternate series of reactions that catabolize glucose to pyruvate using a set of enzymes different from those used in either glycolysis or the pentose phosphate pathway .
  • Glycolysis (from glycose, an older term for glucose + -lysis degradation) is the metabolic pathway that converts glucose C6H12O6, into pyruvate, CH3COCOO− + H+.
  • Distinct features of the Entner–Doudoroff pathway are that it occurs only in prokaryotes and it uses 6-phosphogluconate dehydratase and 2-keto-3-deoxyphosphogluconate aldolase to create pyruvate from glucose.

• Muscle Metabolism

  • Glycolysis the the metabolic reaction which produces two molecules of ATP through the conversion of glucose into pyruvate, water and NADH in the absence of oxygen.
  • Pyruvate is continually processed into lactic acid, with pyruvate accumulation the amount of lactic acid produced is also increased.
  • Whilst the pyruvate generated through glycolysis can accumulate to form lactic acid, it can also be used to generate further molecules of ATP.
  • Mitochondria in the muscle fibers can convert pyruvate into ATP in the presence of oxygen via the Krebs Cycle, generating an additional 30 molecules of ATP.
  • Cellular respiration is limited by oxygen availability and as such lactic acid can still build up if insufficient pyruvate can enter the Krebs Cycle.

• Importance of Glycolysis

  • Through two distinct phases, the six-carbon ring of glucose is cleaved into two three-carbon sugars of pyruvate through a series of enzymatic reactions.
  • The first phase of glycolysis requires energy, while the second phase completes the conversion to pyruvate and produces ATP and NADH for the cell to use for energy.
  • Overall, the process of glycolysis produces a net gain of two pyruvate molecules, two ATP molecules, and two NADH molecules for the cell to use for energy.
  • Following the conversion of glucose to pyruvate, the glycolytic pathway is linked to the Krebs Cycle, where further ATP will be produced for the cell's energy needs.

• Respiration and Proton Motive Force

  • During glycolysis, pyruvate is formed from glucose metabolism.
  • During aerobic conditions, the pyruvate enters the mitochondrion to be fully oxidized by the Krebs cycle.
  • The initial phosphorylation of glucose is required to destabilize the molecule for cleavage into two pyruvate.
  • Glucose + 2 NAD+ + 2 Pi + 2 ADP → 2 pyruvate + 2 NADH + 2 ATP + 2 H+ + 2 H2O + heat
  • Fructose 1, 6-diphosphate then splits into two phosphorylated molecules with three carbon chains that later degrades into pyruvate.

• Control of Catabolic Pathways

  • The last step in glycolysis is catalyzed by pyruvate kinase.
  • The pyruvate produced can proceed to be catabolized or converted into the amino acid alanine.
  • Pyruvate kinase is also regulated by ATP (a negative allosteric effect).
  • If more energy is needed, more pyruvate will be converted into acetyl CoA through the action of pyruvate dehydrogenase.
  • Pyruvate dehydrogenase is also regulated by phosphorylation: a kinase phosphorylates it to form an inactive enzyme, and a phosphatase reactivates it.

• Anaerobic Cellular Respiration

  • Once the lactic acid has been removed from the muscle and circulated to the liver, it can be reconverted into pyruvic acid and further catabolized for energy.
  • Pyruvic acid → CO2 + acetaldehyde + NADH → ethanol + NAD+
  • The first reaction is catalyzed by pyruvate decarboxylase, a cytoplasmic enzyme, with a coenzyme of thiamine pyrophosphate (TPP, derived from vitamin B1 and also called thiamine).
  • A carboxyl group is removed from pyruvic acid, releasing carbon dioxide as a gas.
  • The fermentation of pyruvic acid by yeast produces the ethanol found in alcoholic beverages.