pyruvate

Examples of pyruvate in the following topics:

• 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.

• 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.

• 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.

• The Energy-Releasing Steps of Glycolysis

  • The last step in glycolysis is catalyzed by the enzyme pyruvate kinase (the enzyme in this case is named for the reverse reaction of pyruvate's conversion into PEP) and results in the production of a second ATP molecule by substrate-level phosphorylation and the compound pyruvic acid (or its salt form, pyruvate).

• Connecting Proteins to Glucose Metabolism

  • When deaminated, amino acids can enter the pathways of glucose metabolism as pyruvate, acetyl CoA, or several components of the citric acid cycle.
  • The carbon skeletons of certain amino acids (indicated in boxes) are derived from proteins and can feed into pyruvate, acetyl CoA, and the citric acid cycle.

• ATP in Metabolism

  • For example, the pyruvate dehydrogenase (PDH) complex could be phosphorylated by pyruvate dehydrogenase kinase (PDHK).
  • This reaction leads to inhibition of PDH and its inability to convert pyruvate into acetyl-CoA.

• Acetyl CoA to CO2

  • Acetyl CoA links glycolysis and pyruvate oxidation with the citric acid cycle.

• Epinephrine and Norepinephrine

  • Binding to α-adrenergic receptors inhibits insulin secretion by the pancreas, stimulates glycogenolysis (the breakdown of glycogen) in the liver and muscle, and stimulates glycolysis (the metabolic pathway that converts glucose into pyruvate) in muscle. β-Adrenergic receptor binding triggers glucagon secretion in the pancreas, increased adrenocorticotropic hormone (ACTH) secretion by the pituitary gland, and increased lipolysis by adipose tissue.