Dr.H.MOHAMMAD HANAFI, MBBS (Syd).MS. MEDICAL FACULTY UNAIR

1. CARBOHYDRATE METABOLISM Dr.H.MOHAMMAD HANAFI, MBBS (Syd).MS. MEDICAL FACULTY UNAIR Blog : http//mhanafi123.wordpress.com

2. INTRODUCTION Carbohydrate is a staple food of Indonesian, as many others, specially of Asian and African countries. In general, the source of carbohydrate in food derived from rice, but some are derived from corn, sago, cassava, potatoes, sweet potatoes, and bananas.

3. In rice amylum is the major component. Others are minerals, vitamins, and fibers • Amylum : amylopectin and amylose • Classification of Carbohydrate • Hetero polysaccharides • Homo polysaccharides • Oligosaccharides • Disaccharides • Monosaccharide's

4. Digestion and absorption • Amylase pancreas (alfa amylase) • Endopolysaccharidase : break up alfa link ( 1  4 ), except on the tip of polymers, and near the branch points. • Result of digestion : glucose, maltose, maltotriose, iso maltose, and oligosaccharides (limit dextrins) • Intestinal enzymes : maltase, lactase, sucrase, limit dextrase etc. • Active absorption : glucose and galactose

6. Blood & guts: Putting it together for glucose transport… glucose Fig. 11-44

7. Transfer of Glucose and Other Sugars Through The Lipid Bilayer • Because the lipid bilayer of the eucaryotic plasma membrane is impermeable for hydrophilic molecules, glucose is transported across the plasma membrane by membrane associated carrier proteins, glucose transporters. There are 2 different types of transporter proteins, which mediate the transfer of glucose and other sugars through the lipid bilayer: • Na+-coupled carrier system (SGLT) • The facilitative glucose transporters (GLUT)

10. Glycolysis Glycogenesis Glycogenolysis Pyruvate oxidation TCA Cycle (final common pathway) Hexose Mono-phosphate Shunt or Pentose Phosphate Pathway Gluconeogenesis Uronic Acid pathway Fructose and Galactose metabolism Hexosamine PATH WAYS IN CARBOHYDRATE METABOLISM

11. GLYCOLYSIS • Change : glucose  pyruvate • glucose  lactic acid • Function : produce ATP • Site : cytoplasm • Aerobic glycolysis forms 7 ATP • Anaerobic glycolysis forms 2 ATP

13. Pyruvate Lactate

14. G  G 6P

15. Found in all cells except pancreas Inhibited by ( G 6P ) Km for glucose low Catalyze the reaction Fructose (F)  F 6P Found in liver and pancreas G 6P has no effect Km for glucose high The only enzyme for G  G 6P HEXOKINASEGLUCOKINASE

17. G 6P  F 6P

18. PFK-1 Regulator enzyme F 6P  F 1,6 BP One way reaction

19. Activators : ADP AMP Pi NH3 F 2,6 BP ( fructose 2,6 Bis Phosphate ) F 6 P Inhibitors ATP Citric acid 2,3 BP Glycerate ( in erythrocytes) Free Fatty Acid Acetyl-CoA Ketone bodies PHOSPHO FRUCTO KINASE 1( PFK 1 )

20. Ketone bodies : Acetoacetate Betahydroxy Butyrate Acetone O || C-C-C-COOH O || C-C-C OH | C-C-C-COOH

21. UNIQUE ROLE OF 2,6 BP In the liver • The most potent positive allosteric • activator for enzyme Phosphofructokinase-1 (PFK-1), and • It relieves inhibition of PFK-1 • by ATP, and ↑ affinity for F 6 P • Inhibit Fructose 1,6-bisphosphatase • ( ↑ Km for F 1,6 BP )

22. F 6P  F2,6 BP PFK-2 cAMP Dependent Protein Kinase Protein  Protein P ( few proteins )

23. kinase ATP ADP fructose-2,6-bisphosphate fructose-6-phosphate Pi phosphatase Phosphofructokinase-2 (PFK-2) is also a phosphatase (bifunctional enzyme) • Bifunctional enzyme has two activities: • 6-phosphofructo-2-kinase activity, decreased by phosphorylation • Fructose-2,6-bisphosphatase activity, increased by phosphorylation

24. F 1,6 BP Gld 3P + DHAP

25. In Glycolysis DHAP is converted into glyceraldehyde -3P

26. 6. Glyceraldehyde-3-phosphate Dehydrogenase catalyzes: glyceraldehyde-3-P + NAD+ + Pi 1,3-bisphosphoglycerate + NADH + H+

27. If oxygen available Respiratory Chain in function, by mean of Malate shuttle system oxidizes NADH in the resp. syst ; 2.5 ATP released NAD+ recovered, catalyzed by malate dehydrogenase Enzyme glyceraldehyde 3P dehydrogenase required NAD+ in function If R. C. not in function, NADH will reduces Pyruvate into Lactate

28. Exergonic oxidation of the aldehyde in glyceraldehyde-3-phosphate, to a carboxylic acid, drives formation of an acyl phosphate, a "high energy" bond (~P). This is the only step in Glycolysis in which NAD+ is reduced to NADH.

29. This phosphate transfer is reversible (low ∆G), since one ~P bond is cleaved & another synthesized. The enzyme undergoes substrate-induced conformational change similar to that of Hexokinase.

30. Phosphate is shifted from the OH on C3 to the OH on C2.

31. Fluoride (-) Fluoride in tooth paste inhibits oral bacterial growth F is also used in glucose determination

32. This phosphate transfer from PEP to ADP is spontaneous. • PEP has a larger ∆G of phosphate hydrolysis than ATP. • Removal of Pi from PEP yields an unstable enol, which spontaneously converts to the keto form of pyruvate. • Required inorganic cations K+ and Mg++ bind to anionic residues at the active site of Pyruvate Kinase.

33. Activators : F 1,6 BP In the liver F 1,6 BP able to abolish inhibition of ATP and Alanine Inhibitors : ATP Free Fatty Acid Acetyl CoA Ketone bodies Alanine (in liver only) P y r u v a t e K i n a s eactivity

34. Protein Kinase (P.K.) controls in Glycogen. • cAMP dependent Protein Kinase activated by cAMP. • cAMP synthesized from ATP • enzyme adenylyl cyclase • Glucagon activates adenylyl cyclase (through G protein)

35. 1. PFK-1, with decreasing F2,6 BP. PFK-2-P catalyzes F2,6 BP  F6P + Pi. Active cAMP Dependent P.K. converts PFK-2  PFK-2-P ( ATP  ADP ) 2.Inactive Pyruvate Kinase PEP  P Pyruvate Kinase  PK-P Pyruvate Kinase is phosphorylated by cAMP Dependent P.K. Pyruvate Kinase phosphate (PK-P) is inactive cAMP Dependent Protein Kinase inhibits Glycolysis in two sites

37. If oxygen available for respiratory chain activity, Pyruvate is the end product of Glycolysis with 7 ATP as high energy phosphate. ( older textbook still counting as 8 ATP). In unaerobic Glycolysis of certain type of muscle for sprinters, lack of oxygen cause inactive respiratory chain. NADH will reduces Pyruvate, and Lactate is the final product of Glycolysis. NAD+ is ready as coenzyme for Glyceraldehyde 3P dehydrogenase

38. NAD+ is the target product. Lactate is the by product. Lactate is one of the substrate of gluconeogenesis, will be taken up by the liver and changed into glucose.

39. Glycolysis in Erythrocyte • No mitochondria • No Respiratory enzymes • NADH reduces Pyruvate into Lactate • 2,3 BP Glycerate  drives oxygen dissociation of Oxy hemoglobin to release Oxygen  inhibits PFK-1

40. In the tissue where oxygen required but not ATP, 1,3 BP Glycerate is converted into 2,3 BP Glycerate

41. Lactate release . Tissues that normally derive much of their energy from glycolysis and produce lactate include brain, gastrointestinal tract, renal medulla, retina, and skin. Lactate production is also increased in septic shock, and many cancers also produce lactate.