بسم الله الرحمن الرحيم

Glycolysis By Amr S. Moustafa, M.D.; Ph.D. Assistant Prof. & Consultant, Medical Biochemistry Dept. College of Medicine, KSU amrsm@hotmail.com

Glucose Transport Na+-Independent Facilitated Diffusion Glucose Transporters (GLUT 1-14) With concentration gradient Energy Independent Na+-Monosaccharide Cotransporter: Against concentration gradient Energy dependent Carrier-mediated (SGLT) Coupled to Na+ transport Small intestine, renal tubules & choroid plexus

Glucose Transport: Facilitated Diffusion

Glucose Transporters Tissue-specific expression pattern GLUT-1 RBCs and brain GLUT-2 Liver, kidney & pancreas GLUT-3 Neurons GLUT-4 Adipose tissue & skeletal muscle GLUT-5 Small intestine & testes GLUT-7 Liver (ER-membrane) Functions: GLUT-1, 3 & 4 Glucose uptake from blood GLUT-2 Blood & cells (either direction) GLUT-5 Fructose transport

Glucose Transport & Insulin

Metabolic Pathway Definition Site: Cellular (tissue) and Subcellular Reactions Rate-limiting enzyme(s) Regulatory mechanism(s): Rapid, short-term: Allosteric Covalent modification Slow, long-term: Induction/repression

Glycolysis

Aerobic Vs Anaerobic Glycolysis

Aerobic Glycolysis: Total Vs Net ATP Production

Aerobic Glycolysis-1 Hexokinase Glucokinase

Aerobic Glycolysis-2

Aerobic Glycolysis: 3-5

2 2 Aerobic Glycolysis: 6 -10 2 2 2 2

Aerobic Glycolysis-1 Hexokinase Glucokinase

Hexokinase Vs Glucokinase Site Most tissues Hepatocytes Islet cells (pancreas) Kinetics Low Km Low Vmax High Km High Vmax Regulation G-6-phosphate F-6-phosphate Insulin: Induction Function Low glucose conc. High glucose conc. Glucose sensor

Hexokinase Vs Glucokinase -2

Glucokinase Regulatory Protein

PFK-1 : Regulation

F – 2,6 – Bisphosphate and PFK-2

Aldolase and Triose Isomerase

Glyceraldehyde 3-Phosphate Dehydrogenase 2 2 2 2 2 2

Phospho- glycerate Kinase 2 2 Phospho- glycerate Kinase Substrate- Level Phosphorylation 2 2 2 2

2 2 2 Substrate- Level Phosphorylation 2 2 Pyruvate Kinase 2

Pyruvate Kinase Covalent Modification

Pyruvate Kinase Deficiency Hemolytic Anemia

Summary: Regulation of Glycolysis Regulatory Enzymes (Irreversible reactions): Glucokinase/hexokinase PFK-1 Pyruvate kinase Regulatory Mechanisms: Rapid, short-term: Allosteric Covalent modifications Slow, long-term: Induction/repression Apply the above mechanisms for each enzyme where applicable

Aerobic Glycolysis: ATP Production ATP Consumed: 2 ATP ATP Produced: Substrate-level 2 X 2 = 4 ATP Oxidative-level 2 X 3 = 6 ATP Total 10 ATP Net: 10 – 2 = 8 ATP

Shuttle Mechanisms 2 ATP 3 ATP A. Glycerol-phosphate Shuttle B. Malate - Aspartate Shuttle 3 ATP

Anaerobic Glycolysis

Lactate Dehydrogenase

Lactate Consumption Lactate Pyruvate LD NAD+ NADH Liver: Pyruvate to glucose (Gluconeogenesis) Pyruvate to active acetate (CO2 + H2O, Krebs) Heart: Pyruvate to active acetate (CO2 + H2O, Krebs)

Lactate Lactate in muscle: Muscle cramps Lactate in blood: Lactic acidosis Blood lactate level: Monitors patient’s recovery Oxygen debt

Anaerobic Glycolysis: ATP Production ATP Consumed: 2 ATP ATP Produced: Substrate-level 2 X 2 = 4 ATP Oxidative-level 2 X 3 = 6 ATP Total 4 ATP Net: 4 – 2 = 2 ATP

Anaerobic Glycolysis: RBCs 2,3-BPG Shunt

Glycolysis in RBCs: ATP Production ATP Consumed: 2 ATP ATP Produced: Substrate-level 2 X 2 = 4 ATP 1 X 2 = 2 ATP Oxidative-level 2 X 3 = 6 ATP Total 4 ATP Net: 4 – 2 = 2 ATP 2 – 2 = 0 ATP OR OR

Glycolysis in RBCs: Summary End product: Lactate No net production or consumption of NADH Energy yield: No 2,3-BPG 2 ATP 2,3-BPG shunt 0 ATP PKD hemolytic anemia depends on: Degree of PKD Compensation by 2,3-BPG