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Chapter 19

Chapter 19. Glycolysis - Phase II. All rights reserved. Requests for permission to make copies of any part of the work should be mailed to: Permissions Department, Harcourt Brace & Company, 6277 Sea Harbor Drive, Orlando, Florida 32887-6777. Glycolysis - Second Phase.

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Chapter 19

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  1. Chapter 19 Glycolysis - Phase II All rights reserved. Requests for permission to make copies of any part of the work should be mailed to: Permissions Department, Harcourt Brace & Company, 6277 Sea Harbor Drive, Orlando, Florida 32887-6777

  2. Glycolysis - Second Phase Phase II of Glycolysis ultimately produces 4 ATP Molecules • Net ATP yield for glycolysis is two ATP • Second phase involves two very high energy phosphate intermediates • . • 1,3 BPG (1,3-bisphosphoglycerate) • Phosphoenolpyruvate

  3. Reaction 6 D-Glyceraldehyde-3-phosphate (G-3P) + NAD+ + HPO42- 1,3-Bisphosphoglycerate (1,3-BPG) + NADH

  4. Rx 6: Gly-3-Dehydrogenase Gly-3P is oxidized to 1,3-BPG • Free energy obtained from converting an aldehyde to a carboxylic acid is used to make 1,3-BPG and NADH • DG in erythrocytes = -1.29 kJ/mol • Mechanism involves covalent catalysis and a nicotinamide coenzyme (NAD+/NADH) - make sure you know it!

  5. Reaction 7 1,3-Bisphosphoglycerate (1,3-BPG) + ADP 3-Phosphoglycerate (3-PG) + ATP

  6. Rx 7: Phosphoglycerate Kinase ATP synthesis from a high-energy phosphate • Often referred to as "substrate-level phosphorylation" • DG in erythrocytes = +0.1 kJ/mol

  7. Reaction 8 3-Phosphoglycerate (3-PG) 2-Phosphoglycerate (2-PG)

  8. Rx 8: Phosphoglycerate Mutase Phosphoryl group is transferred from C-3 to C-2 • Rationale for this enzyme - repositions the phosphate to make phosphoenol pyruvate (PEP) in next step • DG in erythrocytes = +0.83 kJ/mol • Note that phospho-histidines are intermediates

  9. Reaction 9 2-Phosphoglycerate (2-PG) Phosphoenolpyruvate (PEP)

  10. Rx 9: Enolase 2-P-Gly to PEP • Overall Gº’ is +1.8 kJ/mol • G in erythrocytes is +1.1 kJ/mol • How can this reaction create a PEP? • "Energy content" of 2-PG and PEP are quite similar • Enolase simply converts 2-PG to a molecule from which more energy can be released via hydrolysis

  11. Reaction 10 Phosphoenolpyruvate (PEP) + ADP Pyruvate + ATP

  12. Rx 10: Pyruvate Kinase PEP to Pyruvate makes ATP • These two ATP (from one glucose) can be viewed as the "payoff" of glycolysis • Large, negative G (-23.0 kJ/mol in erythrocytes !) • A regulated enzyme • Allosterically activated by AMP, F-1,6-bisP • Allosterically inhibited by ATP and acetyl-CoA • Make sure you understand the keto-enol equilibrium of pyruvate

  13. The Fate of NADH and PyruvateAerobic or anaerobic?? • NADH is energy rich/provides reducing equivalents - two possible fates: • If O2 is available, NADH is re-oxidized in the electron transport pathway, which produced ATP by oxidative phosphorylation • In anaerobic conditions, NADH is re-oxidized by lactate dehydrogenase (LDH), providing additional NAD+ for more glycolysis

  14. The Fate of NADH and PyAerobic or anaerobic?? • Pyruvate is also energy rich - two possible fates: • aerobic: citric acid cycle • anaerobic: LDH makes lactate

  15. Energetics of Glycolysis • See Figure 19.31 • Standard state G°’ values are scattered: + and - • G in cells is revealing: • Most values near zero • 3 of 10 Rxns have large, negative G°’ • Large negative G° Rxns are sites of regulation! • Study, but you need not memorize Table 19.1

  16. Other Substrates for Glycolysis Fructose, mannose and galactose • Fructose and mannose are routed into glycolysis by fairly conventional means. See Figure 19.32 • Galactose is more interesting - the Leloir pathway "converts" galactose to G-6-P • See Figure 19.33

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