Glycolysis and Regulation PDF

BIOENERGETICS AND INTEGRATED METABOLISM (BIOC202) GLYCOLYSIS AND RED BLOOD CELLS (RBC) Glucose metabolism role in RBC functions: 1) RBCs rely solely on glycolysis to generate adenosine triphosphate (ATP); 2) approximately 25% of glucose in RBCs is used to produce the RBC spe...

BIOENERGETICS AND INTEGRATED METABOLISM (BIOC202) GLYCOLYSIS AND RED BLOOD CELLS (RBC) Glucose metabolism role in RBC functions: 1) RBCs rely solely on glycolysis to generate adenosine triphosphate (ATP); 2) approximately 25% of glucose in RBCs is used to produce the RBC specific metabolite 2,3-bisphosphoglycerate (2,3-BPG) for haemoglobin O2 affinity modulation; 3) RBCs depend on the oxidative branch of the pentose phosphate pathway (PPP) to generate reducing equivalents (NADPH) to preserve glutathione homeostasis and counteract oxidative stress.” (Sun et al., 2017)  IMPORTANCE OF GLYCOLYSIS IN RBCs 2- O OPO 3 C Bisphosphoglycerate mutase H C OH 2- CH2 OPO3 1,3-Bisphosphoglycerate (1,3-BPG) 2ADP - COO 7 Phosphoglycerate 2- kinase H C OPO3 ( PGK) 2ATP 2- CH2 OPO3 2,3-Bisphosphoglycerate (2,3-BPG) 3-Phosphoglycerate (3PG) - COO H2O 2,3-Bisphosphoglycerate H C OH p hosphatase 2- CH2 OPO3 Pi  IMPORTANCE OF GLYCOLYSIS Production of 2,3-bisphosphoglycerate (2,3-BPG), an allosteric effector that promotes the release of oxygen from hemoglobin. 2,3-bisphosphoglycerate interacts with the subunits of hemoglobin thereby decreasing its affinity for oxygen. Red blood cells contain the enzyme bisphosphoglycerate mutase that catalyses the transfer of a phosphoryl group from C-1 to C-2 of 1,3- bisphosphoglycerate, to form 2,3-BPG.  IMPORTANCE OF GLYCOLYSIS The enzyme 2,3-bisphosphoglycerate phosphatase then converts 2,3-BPG to 3-phosphoglycerate which can re-enter the glycolytic pathway and be converted to pyruvate. These steps bypass step 7 of the glycolytic pathway during which ATP is generated. Thus, in exchange for decreased ATP production, there is a regulated supply of 2,3-BPG that is crucial for release of O2 from hemoglobin.  ARESENATE POISONING Arsenic and phosphorous is in Group V of the periodic table Arsenate is an analogue of inorganic phosphate and can replace a phosphate group in 1,3-bisphospholycerate to give arseno-3- phosphoglycerate Arseno-3-phosphoglycerate can be rapidly hydrolyzed in water to produce 3- phosphoglycerate Step 7 of glycolysis is by-passed – no net yield of ATP ARSENATE POISONING O 2- O OPO3 O O As O C C O H C OH H C OH 2- 2- CH2 OPO3 CH2 OPO3 1,3-Bisphosphoglycerate (1,3-BPG) 1-Arseno-3-phosphoglycerate 2ADP H 2O 7 Phosphoglycerate non-enzymatic kinase 2ATP (PGK) AsO4 3- 3-Phosphoglycerate (3PG) 3-Phosphoglycerate (3PG) - - COOH COOH H C OH H C OH 2- 2- CH2 OPO3 CH2 OPO3  REGULATION OF GLYCOLYSIS First step of regulation - glucose transport into the cells via glucose transporters Intestinal and kidney cells have Na+-dependent co-transporters called SGLT1 – glucose moves in by passive transport via facilitated diffusion The GLUT family makes up the other hexose transporters: GLUT 1 & GLUT 3 – present in nearly all mammalian cells, continually transports glucose at a constant rate GLUT 2 – present in liver cells GLUT 4 – present in skeletal muscle cells and adipocytes. Insulin promotes rapid uptake of glucose by increasing the number of GLUT 4 receptors on the cell membrane GLUT 5 – transports glucose in the small intestine GLUT 7 – transports glucose-6-phosphate from the cytosol to the ER.  REGULATION OF GLYCOLYSIS Three enzymes i. Hexokinase – inhibited by glucose-6- phosphate ii. Phosphofructokinase (PFK) - inhibited by [ATP] and citrate - activated by [AMP] and fructose-2.6- bisphosphate. (When present in high amount, Fructose-6- phosphate can be converted to fructose-2,6- bisphosphate) iii. Pyruvate kinase - inhibited by [ATP] - activated by fructose-2,6-bisphosphate  REGULATION OF GLYCOLYSIS i. Hexokinase – inhibited by glucose-6-phosphate  REGULATION OF GLYCOLYSIS ii. Phosphofructokinase (PFK) - inhibited by [ATP] and citrate - activated by [AMP] and fructose-2.6- bisphosphate. When present in high amount, fructose-6- phosphate can be convertedto fructose-2,6- bisphosphate) ii. Phosphofructokinase (PFK) (contd) Excess Fructose-6-phosphate is converted to fructose-2,6-bisphosphate using the enzyme Phosphofructokinase-2 (PFK-2) Thus presence of fructose-2,6-bisphosphate indicates that lots of fructose-6- phosphate is present and thus glycolysis must occur FBPase-2 = Fructose-2,6-bisphosphatase-2  REGULATION OF GLYCOLYSIS iii. Pyruvate kinase - inhibited by [ATP] - activated by fructose-2,6-bisphosphate