Glycolysis & related phenomena

Glycolysis & related phenomena

1. BIOCHEMISTRY Glycolysis and related phenomena

2. AGENDA: Glycolysis – (from the Greek words γλυκυς – sweet or sugar; λυσις – dissolution) – is a universal pathway in the living cell. This pathway is often reffered to as Embden-Meyerhof pathway .

3. Glycolysis is the sequence of reactions that converts glucose into pyruvate (or lactate) with the concomitant productions of ATP. In aerobic organisms, glycolysis is the prelude to the citric acid cycle and the electron-transport chain, which together harvest most of the energy contained in glucose. Under aerobic conditions, pyruvate enters mitochondria, where it is completely oxidized to CO 2 and H 2 O. If the supply of oxygen is insufficient, as in actively contracting muscle, pyruvate is converted into lactate. In some anaerobic organisms, such as yeast, pyruvate is transformed into ethanol.

4. Glycolysis is listed among major pathways of carbohydrate metabolism, mainly they are as follows: - glycolysis (oxidation of G [ lucose ] to pyruvate/lactate) - citric acid cycle (oxidation of Acetyl-CoA to CO 2 ) - gluconeogenesis (synthesis of G from non-carbonic precursors: amino acids, glycerol etc.) - glycogenesis (formation of glycogen from G ) - glycogenolis (breakdown of glycogen to G ) - galactose methabolism (conversion of galactose to G and synthesis of lactose) - fructose metabolism (oxidation of fructose to pyruvate) - hexose monophosphat shunt (pentose phosphat pathway of G direct oxidation to CO 2 and H 2 O) - uronic acid pathway (convertation of G to glucuronic acid, pentoses [even to ascorbinic acid but not in man!]) - amino sugar and mucopolysaccharide metabolism (the synthesis of amino sugars for the formation of mucopolysaccharides and glycoproteins).

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6. Pyruvate (pyruvic acid) and related compounds

7. Main types of glycolysis reactions (1) – Phosphoryl transfer – phosphoryl group is transferred from ATP to a glycolitic intermediate, or vice versa

8. Main types of glycolysis reactions (2) – Phosphoryl shift – phosphoryl group is shifted within a molecule from one oxygen atom to another

9. Main types of glycolysis reactions (3) – Isomerization – a ketose is converted into aldose, or vice versa

10. Main types of glycolysis reactions (4) – Dehydratation – a molecule of water is eliminated

11. Main types of glycolysis reactions (5) – Aldol cleavage – a carbon-carbone bond is split in a reversal of an aldol condensation

12. Fates of Glucose

13. There are two pathways of glycolysis reactions: -anaerobic (absence of oxygen: leads to lactate) -aerobic (presence of oxygen: lead to pyruvate) [dichotomic degrading: διχα- – divided into two parts] [apotomic degrading: απο- – cleavage] – glycolysis is a pathway for ATP synthesis in tissues lacking mitochondria (erythrocytes, cornea, lens etc) – glycolysis is essential for brain – glycolysis is a central metabolic pathway with many intermediates providing branch point to other pathways

14. Main features of Gly c oly s is

15. Generally the glycolysis pathway can be divided into three distinct phases I. Energy investment phase ( G is irreversibly phosphorylated to Glucose 6-phosphate by hexokinase or glucokinase [isoenzymes] dependent on ATP and Mg 2+ ) II. Splitting phase (six carbon fructose 1,6-bisphosphate is split by aldolase [hence the name lysis ] into two three-carbon compounds: glyceraldehyde 3-phosphate and dihydroxyacetone phosphate) III. Energy generating phase (glyceraldehyde 3-phosphate dehydrogenase converts glyceraldehyde 3-phosphate to 1,3-bisphosphoglycerate it is involved in the formation of NADH+H + and high energy compound: 1,3-bisphospho- glycerate [iodoacetate and arsenate inhibit the enzyme])

16. Glucose → Glucose 6-phosphate [1°-irreversible] (hexokinase) [+ATP+divalent metal] Hexokinase (glucokinase) – like all other kinases, requires Mg 2+ (or another divalent metal ion such as Mn 2+ )

17. Glucose 6-phosphate → Fructose 6-phosphate [2°] (phosphoglucose isomerase)

18. Fructose 6-phosphate → Fructose 1,6-bisphosphate [3° -irreversible ] (phosphofructokinase) [+ATP Mg 2+ ]

19. Fructose 1,6-bisphosphate → Dihydroxyacetone phosphate [4°] + Glyceraldehyde 3-phosphate (aldolase) triose phosphate [phosphotriose] isomerase convert Dihydroxyacetone phosphate to Glyceraldehyde 3-phosphate

20. Glyceraldehyde 3-phosphate oxydated → 1,3-bisphosphoglycerate [5°] (Glyceraldehyde 3-phosphate dehydrogenase) [+NAD+P i ]

21. 1,3-bisphosphoglycerate → 3-phosphoglycerate [6°] (phosphoglyceratekinase) [ADP (Mg 2+ ) → ATP]

22. 3-phosphoglycerate → 2-phosphoglycerate [7°] (phosphogyceromutase)

23. 3-phosphoglycerate → phosphoenolpyruvate [8°] (enolase) [Mg 2+ ]

24. Phosphoenolpyruvate → pyruvate [9°-irreversible] (pyruvatekinase) [ADP (Mg 2+ ) → ATP]

25. Summary for glycolysis reartions: Glucose + [2ADP + 2NAD + + 2P i ] → 2 Pyruvate + [2ATP + 2NADH + 2H + + 2H 2 O]

26. Generation of ATP in Glucose metabolism

27. Regulation of glycolysis The three enzymes: Hexocinase (and glucokinase) Phosphofructokinase Pyruvate kinase are catalysing the irrevrsible reactions, what can be considered as regulation of glycolysis Hexokinase – is inhibited by glucose-6-phospate Phosphofructokinase – allosteric enzyme regulated by allosteric effectors, most important regularory enzyme in glycolysis – it catalyses the rate limiting committed step, inhibited by ATP, citrate and H+ ions (low pH); fructose 2,6- bisphosphate, ADP, AMP and Pi – are allosteric activators Pyruvate kinase – is inhibited by ATP and activated by fructose 1,6- bisphosphate

28. Regulation of fructose 2,6 bisphosphate Phospho-fructokinase 2 – allosteric enzyme regulated by allosteric effectors, most important regularory enzyme in glycolysis – it catalyses the rate limiting committed step, inhibited by ATP, citrate and H + ions (low pH); fructose 2,6-bisphosphate, ADP, AMP and P i – are allosteric activators [in fact, the combined name of phosphofructokinase 2/fructose 2,6 bisphosphatase is used to refer to the enzyme that synthesis and degrades fructose 2,6 bisphosphate – bifunctional enzyme]

29. Regulation of pyruvate kinase pyruvate kinase is inhibited by ATP, and activated by fructose 1,6-bisphospate. pyruvate kinase is actove in dephosphorylated state and inactive (b) in phosphorylated state. Inactivation of pyruvate kinase by phosphorylation is brought about by cAMP-dependent protein kinase. The hormone – glucagon – inhibits hepatic glycolysis by this mechanism

30. Regulation of glycolysis Pasteur effect – inhibition of glycolysis by oxygen (aerobic condition) Crabtree effect – the phenomenon of inhibition of oxygen consumption by the addition of glucose to tissues having high aerobic glycolysis. This is opposite to the Pasteur effect – is due to increased competition of glycolysis for inorganic phosphate (Pi) and NAD + which limits their availability for phosphorylation and oxidation.

31. Rapaport-Leubering cycle for the synthesis of 2,3- bisphosphoglycerate This is a supplementary pathway to glycolysis which is operative in the erythrocytes of man and other mammals. This cycle is mainly concerned with the synthesis of 2,3-bisphosphoglycerate in the red blood cells.

32. Pyruvate (enol) → Pyruvate (keto) (spontaneously) and → L-Lactate (lactate dehydrogenase)

33. Main source of Glucose for glycolysis is Glycogen

34. Some poli- and disaccharides are hydrolyzed to monosaccharides which directly cannot enter the glycolysis.

35. Entry of Fructose, Galactose, and Mannose into Glyc o lysis

36. Galactose → Glucose (uridin diphosphate [UDP] + NAD + )

37. Pyruvate is the main source of Acetyl-CoA (catalyzed by pyruvate dehydrogenese)

38. Conversion of pyruvate to acetyl CoA Pyruvate is conversed to acetyl CoA by oxidative decarboxylation. This is an irreversible reaction, catalysed by a multienzyme complex – pyruvate dehydrogenase complex, which is found in the mitochondria. High activities of pyruvate dehydrogenase complex are found in cardiac muscle and kidney. It requires five cofactors (coenzymes): thiamine pyrophosphate (TPP), lipoamide, flavin adenin dinucleotid(FAD), coenzyme A, and nicotine adenin dinucleotid (NAD + ) - (lipoamide contains lipoic acid linked to ε-amino group of lysine)

39. Fatty acids – by reactions of β-oxidation, also, – leads to Acetyl-CoA

40. Acetyl-CoA it the main source of Energy

41. Cycle of citric acid (Kreb’s cycle) [tricarboxylic acid cycle]

42. and it is a starting point of some very important substance synthesis named CHOLESTEROL it leads to steroid hormones, bile acids, membrane construction It is very important in genesis of vascular pathology

43. Cholesterol synthesis pathway isoprenoid unit (5C) ( isopren СН 2 =С(СН 3 )-СН=СН 2 )

44. Cholesterol (1-step) Acetoacetyl CoA (thiolase)

45. Cholesterol (2-step) β-hydroxy β-methylglutaryl CoA (hydroxy-methylglutaril CoA synthase)

46. Cholesterol (3-step) mevalonate (6C) (β-hydroxy β-methylglutaril CoA reductase) Hydroxy- methylglutaril CoA reductase is inhubited by statins and fibrates

47. Cholesterol (4-step) 5-phosphomevalonate (6C) (mevalonate kinase)

48. Cholesterol (5-step) 5-pyrophosphomevalonate (6C) (phosphomevalonate kinase)

49. Cholesterol (6-step) 3-phospho 5-pyrophosphomevalonate (kinase)

50. Cholesterol (7-step) isopentenyl pyrophosphate (5C) (pyrophosphomemalonate decarboxylasae)

51. Cholesterol (8-step) dimethylallyl pyrophosphate (5C) (isopentenyl pyrophoshate isomerase)

52. Cholesterol (9-step) geranyl pyrophosphate (10C) ( cis -prenyltransferase)

53. Cholesterol (10-step) farnesyl pyrophosphate (15C) ( cis -prenyltransferase) + dimethylallyl pyrophosphate (5C)

54. Cholesterol (11-step) squalene (30C) (squalene synthase)

55. Cholesterol (12-step) lanosterol (30C) (epoxidase+hydrolase+cyclase)

56. Cholesterol (13-step + ~ 19 reactions ) cholesterol (27C) (with different enzymes participation)

57. Cholesterol structure

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