Glycolysis and the Catabolism of Hexoses

Glycolysis and the Catabolism of Hexoses Eduard Büchner 1860 - 1917 (Anaerobic Fermentation) Fritz A. Lipmann 1899 – 1986 (Discovered Coenzyme A) Sir Hans A. Krebs 1900 – 1981 (Citric Acid Cycle) Lipmann and Krebs shared the 1953 Nobel Prize for Physiology or Medicine Fates of Glucose Fig 15-01.GIF 1 Two phases of Glycolysis: Preparatory Phase C6 9 2 C3 Fig 15-02.GIF Two phases of Glycolysis: Energy Conservation Phase 2 C3 9 2 C3 2 ATP Fig 15-02.GIF 2 Glycolysis Stage I: Preparatory Phase (Rxn 1 & -1) 6 HO 5 O "Tags" glucose to keep it in the cell ∆G B N = - 16.7 kJ/mol OH 4 OH 1 3 2 OH +1 - glucokinase (or hexokinase) OH -1 - glucose-6-phosphate phosphatase glucose (G) Pi ATP +1 -1 H2O PiO ∆G B N = - 13.8 kJ/mol Removes Pi - active only in gluconeogenesis ADP nonliver 6 O 5 OH 4 1 OH 2 3 OH liver OH glucose-6-phosphate (G6P) Glycolysis Stage I: Preparatory Phase (Rxn 1) 6 HO 5 O "Tags" glucose to keep it in the cell ∆G B N = - 16.7 kJ/mol OH 4 OH 1 3 2 OH +1 - glucokinase (or hexokinase) OH -1 - glucose-6-phosphate phosphatase glucose (G) Pi +1 -1 H2O PiO B ∆G N = - 13.8 kJ/mol Removes Pi - active only in gluconeogenesis ADP 6 5 O OH 4 OH ATP 1 3 2 OH OH glucose-6-phosphate (G6P) 3 Glycolysis Stage I: Preparatory Phase (Rxn 2) PiO 6 O 5 phosphohexose isomerase OH 4 OH 1 2 3 OH OH glucose-6-phosphate (G6P) 2 - glucose-6-phosphate isomerase B ∆G N = + 1.67 kJ/mol 2 O 6 PiO 1 5 OH 2 Isomerization of C6 in preparation for the cleavage reaction OH OH 4 3 OH fructose-6-phosphate (F6P) º Glycolysis Stage I: Preparatory Phase (Mechanism 2a) 4 º Glycolysis Stage I: Preparatory Phase (Mechanism 2b) º Glycolysis Stage I: Preparatory Phase (Mechanism 2c) CH2OH C O HO C H H C OH H C OH CH2OH 1 2 3 HO O 6 OH 5 4 4 5 1 3 OH 2 OH OH 6 OPEN CHAIN FORM α-D-FRUCTOFURANOSE 5 Glycolysis Stage I: Preparatory Phase (Rxn 3 & -3) O 6 PiO OH 1 5 OH 2 2nd phosphorylation to commit glucose into glycolysis OH B ∆G N = - 14.2 kJ/mol 4 3 OH fructose-6-phosphate (F6P) Pi +3 -3 H2O +3 - phosphofructokinase -3 - fructose-1,6-bisphosphate phosphatase ATP B ∆G N = - 16.7 kJ/mol Removes Pi - active only in gluconeogenesis ADP 6 PiO 1 O OH 5 2 4 OPi OH 3 OH fructose-1,6-bisphosphate (F6P) Glycolysis Stage I: Preparatory Phase (Rxn 4 & 5) 1 O 6 PiO OH 5 2 4 OPi OH 4 - aldolase 3 OH B ∆G N = + 24.0 kJ/mol fructose-1,6-bisphosphate (F6P) 4 PiO 6 1 OH OPi + 5 Cleavage of C6 into 2 x C3 fragments 4 OH 2 OH 3 O glyceraldehyde-3-phosphate dihydroxyacetone phosphate (DHAP) (GAP) CH 5 H C OH 6 CH2OPi (GAP) 1 CH2OPi 2 C 3 CH2OH 5 Isomerization of C3 to interconvert forms B ∆G N = - 24.0 kJ/mol O 4 5 - triosephosphate isomerase B ∆G N = - 7.6 kJ/mol O (DHAP) (over for Stage II starting with 2 GAP) 6 ALDOLASE º º º º Glycolysis Stage I: Preparatory Phase (Rxn 5) glyceraldehyde-3-phosphate (GAP) dihydroxyacetone phosphate (DHAP) O 4 CH 5 H C OH 6 CH2OPi (GAP) 5 1 CH2OPi 2 C 3 CH2OH O (DHAP) 5 - triosephosphate isomerase B ∆G N = - 7.6 kJ/mol Isomerization of C3 to interconvert forms 7 Triosephosphate Isomerase Mechanism Glycolysis Stage II: Energy Conservation Phase (Rxn 6) ***2 x all intermediates*** O 3,4 CH GLYCOLYSIS STAGE II: PREPARATORY PHASE 2,5 H C OH 1,6 CH2OPi glyceraldehyde-3-phosphate (GAP) Pi + NAD+ 6 (Energy Conservation Phase) 6 - glyceraldehyde-3-phosphate dehydrogenase ∆G B N = + 6.3 kJ/mol NADH + H+ O 3,4 H 2,5 1,6 O C O P O C OH O CH2OPi 1,3-bisphosphoglycerate (1,3-BPG) substrate-level oxidative phosphorylation: process of oxidation coupled to phosphorylation Step 6 alone is an example which generates 1st high energy phosphate compound responsible for the net 2 ATP/glucose. Step 6 + Step 7 can also be considered to be substrate-level oxidative phosphorylation for the formation of ATP 8 Glycolysis Stage II: Energy Conservation Phase (Rxn 6) Fig 15-05.GIF Glycolysis Stage II: Energy Conservation Phase (Rxn 6) GLYCERALDEHYDE-3-PHOSPHATE DEHYDROGENASE O H2N O H C H C + N R **NAD (oxidized form) O H C OH + HO P O OH CH2OPi glyceraldehyde-3-Pi H2N O O H H C + N R **NADH O C O P- O O H C OH + H+ CH2OPi 1,3-bisphosphoglycerate (reduced form) O INHIBITOR WITH RESPECT TO Pi: HO As O(and uncoupler of substrate-level oxidative phosphorylation) OH 9 Glycolysis Stage II: Energy Conservation Phase (Rxn 6) GLYCERALDEHYDE-3-PHOSPHATE DEHYDROGENASE O H2N O H O C H C + + HO P O- H C OH N R H2N C O P- O O H C OH + OH CH2OPi N glyceraldehyde-3-Pi **NAD + H+ CH2OPi R **NADH (oxidized form) O O O H H C 1,3-bisphosphoglycerate (reduced form) ORDERED TRI BI MECHANISM NAD+ E NAD+: G3P ENAD+ E 1,3-BPG Pi G3P E NADH : G'3P NADH E NADH E NADH : 1,3 BPG E Glycolysis Stage II: Energy Conservation Phase (Rxn 6) OPO3-2 - OPO3 2 1 C N CHOH H 4 O H R CH2 CH2 CHOH R H H S N N O P H O N H H C H 3 O HO O H S N H CH2 CHOH N N H OPO3-2 CH2 R O S OPO3-2 2 C O O H N N H P OH O H R N H CHOH C S O O HO H N N H P OH O 10 Glycolysis Stage II: Energy Conservation Phase (Rxn 7) O O C O P O 2,5 H C OH O 3,4 1,6 2x all intermediates in Stage II CH2OPi 1,3-bisphosphoglycerate (1,3-BPG) ADP 7 ATP 7 - phosphoglycerate kinase B ∆G N = - 18.5 kJ/mol O C O 3,4 H 2,5 1,6 C 1st energy conservation step OH CH2OPi 3-phosphoglycerate (3PG) Glycolysis Stage II: Energy Conservation Phase (Rxn 8) 2x all intermediates in Stage II O C O 3,4 H 2,5 1,6 C OH CH2OPi 3-phosphoglycerate (3PG) 8 - phosphoglycerate mutase B ∆G N = + 4.4 kJ/mol 8 O 3,4 H 2,5 C O C prepares C3 for generation of 2nd high energy phosphate compound OPi CH2OH 2-phosphoglycerate (2PG) 1,6 11 Glycolysis Stage II: Energy Conservation Phase (Rxn 8) º 2,3-BPG º º To control oxygen binding to Hb º http://www.med.unibs.it/~marchesi/mutase.html Glycolysis Stage II: Energy Conservation Phase (Rxn 9) O 3,4 H 2,5 C O C OPi CH2OH 2-phosphoglycerate (2PG) 1,6 9 H2O H2 O O 3,4 C O 2,5 C 1,6 CH2 OPi 9 - enolase B ∆G N = + 7.5 kJ/mol generation of 2nd high energy phosphate compound phosphoenolpyruvate (PEP) Write a mechanism for the dehydration using acid/base catalysts 12 Glycolysis Stage II: Energy Conservation Phase (Rxn 10) O 3,4 C O 2,5 C 1,6 CH2 Write a mechanism for the phosphate transfer. What intermediate do you have to write? What is the process by which that intermediate is converted to pyruvate? OPi phosphoenolpyruvate (PEP) ADP 10 ATP 10 - pyruvate kinase B ∆G N = - 31.4 kJ/mol O 3,4 2nd energy conservation step 2,5 1,6 C O C O CH3 pyruvate (PYR) Glycolysis Stage II: Energy Conservation Phase (Rxn 11) 11 - lactate dehydrogenase B ∆G N = - 25.1 kJ/mol 3,4 2,5 1,6 C O C O Regeneration of active oxidant O O CH3 pyruvate (PYR) 3,4 NAD+ NADH + H+ HO 11 2,5 1,6 C O C H CH3 L-lactate (LAC) Write a mechanism for the reduction of pyruvate to L-lactic acid 13