Anaerobic glycolysis

Anaerobic glycolysis is the transformation of glucose to lactate when limited amounts of oxygen (O₂) are available. ^[1] This occurs in health as in exercising and in disease as in sepsis and hemorrhagic shock. ^[1] providing energy for a period ranging from 10 seconds to 2 minutes. During this time it can augment the energy produced by aerobic metabolism but is limited by the buildup of lactate. Rest eventually becomes necessary. ^[2] The anaerobic glycolysis (lactic acid) system is dominant from about 10–30 seconds during a maximal effort. It produces 2 ATP molecules per glucose molecule, ^[3] or about 5% of glucose's energy potential (38 ATP molecules). ^{[4] [5]} The speed at which ATP is produced is about 100 times that of oxidative phosphorylation. ^[1]

Anaerobic glycolysis is thought to have been the primary means of energy production in earlier organisms before oxygen was at high concentration in the atmosphere and thus would represent a more ancient form of energy production in cells.

In mammals, lactate can be transformed by the liver back into glucose using the Cori cycle.

Fates of pyruvate under anaerobic conditions:

1. Pyruvate is the terminal electron acceptor in lactic acid fermentation.
   When sufficient oxygen is not present in the muscle cells for further oxidation of pyruvate and NADH produced in glycolysis, NAD+ is regenerated from NADH by reduction of pyruvate to lactate. ^[4] Lactate is converted to pyruvate by the enzyme lactate dehydrogenase. ^[3] The standard free energy change of the reaction is -25.1 kJ/mol. ^[6]
2. Ethanol fermentation
   Yeast and other anaerobic microorganisms convert glucose to ethanol and CO₂ rather than pyruvate. Pyruvate is first converted to acetaldehyde by enzyme pyruvate decarboxylase in the presence of Thiamine pyrophosphate and Mg++. Carbon-dioxide is released during this reaction. Acetaldehyde is then converted to ethanol by the enzyme alcohol dehydrogenase. NADH is oxidized to NAD+ during this reaction.

See also

• Aerobic glycolysis
• Lactate shuttle hypothesis
• Lactic acidosis

References

1. Stojan, George; Christopher-Stine, Lisa (2015-01-01), Hochberg, Marc C.; Silman, Alan J.; Smolen, Josef S.; Weinblatt, Michael E. (eds.), "151 - Metabolic, drug-induced, and other noninflammatory myopathies", Rheumatology (Sixth Edition), Philadelphia: Content Repository Only!, pp. 1255–1263, ISBN   978-0-323-09138-1 , retrieved 2020-11-02
2. Pigozzi, Fabio; Giombini, Arrigo; Fagnani, Federica; Parisi, Attilio (2007-01-01), Frontera, Walter R.; Herring, Stanley A.; Micheli, Lyle J.; Silver, Julie K. (eds.), "CHAPTER 3 - The Role of Diet and Nutritional Supplements" , Clinical Sports Medicine, Edinburgh: W.B. Saunders, pp. 23–36, doi:10.1016/b978-141602443-9.50006-4, ISBN   978-1-4160-2443-9 , retrieved 2020-11-02
3. Bender, D. A. (2003-01-01), "GLUCOSE | Function and Metabolism", in Caballero, Benjamin (ed.), Encyclopedia of Food Sciences and Nutrition (Second Edition), Oxford: Academic Press, pp. 2904–2911, ISBN   978-0-12-227055-0 , retrieved 2020-11-02
4. Kantor, PAUL F.; Lopaschuk, GARY D.; Opie, LIONEL H. (2001-01-01), Sperelakis, NICHOLAS; Kurachi, YOSHIHISA; Terzic, ANDRE; Cohen, MICHAEL V. (eds.), "CHAPTER 32 - Myocardial Energy Metabolism" , Heart Physiology and Pathophysiology (Fourth Edition), San Diego: Academic Press, pp. 543–569, doi:10.1016/b978-012656975-9/50034-1, ISBN   978-0-12-656975-9 , retrieved 2020-11-02
5. Engelking, Larry R. (2015-01-01), Engelking, Larry R. (ed.), "Chapter 24 - Introduction to Glycolysis (The Embden-Meyerhoff Pathway (EMP))" , Textbook of Veterinary Physiological Chemistry (Third Edition), Boston: Academic Press, pp. 153–158, doi:10.1016/b978-0-12-391909-0.50024-4, ISBN   978-0-12-391909-0 , retrieved 2020-11-02
6. Cox Michael M, Nelson David L (2008). "Chapter 14: Glycolysis, Gluconeogenesis, and the Pentose Phosphate Pathway". Lehninger Principles of Biochemistry (5 ed.). W H Freeman & Co. pp.  527–568. ISBN   978-1429222631.