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Chapter 20 The Calvin cycle and P entose P hosphate P athway  an evolutionary kinship

Chapter 20 The Calvin cycle and P entose P hosphate P athway  an evolutionary kinship. § Dark reaction (Calvin cycle). § Light reaction (Ch. 19). Calvin cycle – take place in the stroma of chloroplast. 3 stages:. or 10.

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Chapter 20 The Calvin cycle and P entose P hosphate P athway  an evolutionary kinship

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  1. Chapter 20 The Calvin cycle and Pentose Phosphate Pathway an evolutionary kinship § Dark reaction (Calvin cycle) § Light reaction (Ch. 19)

  2. Calvin cycle– take place in the stroma of chloroplast 3 stages: or 10 6CO2 + 18 ATP + 12 NADPH + 12 H2O  C6H12O6 + 18 ADP + 18 Pi + 12 NADP+ + 6 H+

  3. Ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) catalyzes the rate-limiting step G°=  12.4 kcal/mol

  4. Tracing the fate of CO2(C3 plant) time course

  5. Rubisco  located on the stromal surface of the thylakoid membrane;  probably the most abundant protein in the biosphere;  8 large subunits: each contains catalytic site and regulatory site 8 small subunits: enhance the catalytic activity of L subunits  a slow enzyme (kcat), 3 s-1  requires amagnesiumion and a CO2 other than the substrate CO2  the activity increase markedly on illumination (CAM?)  also catalyzes oxygenase reaction –photorespiration Rubisco activase faciliate How to mimic?

  6. Taiz and Zeiger, 2006 substrate active form Rubisco activase: exhibit an ATPase activity two polypeptide (42 and 47 kDa)

  7. Oxygenase activity of Rubisco  still requires that Lys210 be in the carbamate form no CO2, no oxygenation 2C  The rate of carboxylation is four times that of oxygenation under normal conditions.  Stromal [CO2]: 10  M, [O2]: 250  M  A salvage pathway for phosphoglycolate

  8. Photorespiration  a wasteful process ¾ C

  9. TPP

  10. 23C  16C + 33C  35C

  11. 5C

  12. 35C + 3 H2O 6(3CO2)   53C 10 6 CO2 + 18 ATP + 12 NADPH + 12 H2O  C6H12O6 + 18 ADP + 18 Pi + 12 NADP+ + 6 H+ Rubisco activity analysis?

  13. Synthesis ofsucroseandstartch in cytoplasm and chloroplasts, separately. ADP-G starch Phosphate translocator (diel) Storage forms in plants: sucrose, starch, fructan

  14. § 20.2 The activity of the Calvin cycle depends on environmental conditions alkaline pH and [Mg2+] rhythm phenomenon

  15. Thioredoxin: plays a key role in the regulating the Calvin cyclea 12 kDa protein that have a catalytically active disulfide group containing two redox-active cysteine residues (-Trp-Cys-Gly-Pro-Cys).

  16. Calvin cycle

  17. C4 pathway of tropical plants sugar cane  concentrating CO2 , little phosphorespiration Kranz (wreath) cells: Malate dehydrogenase Malic enzyme PEP carboxylase 2 ATP Pyruvate-Pi dikinase 6 CO2 + 30 ATP + 12 NADPH + 24 H2O  C6H12O6 + 30 ADP + 30 Pi + 12 NADP+ + 18 H+

  18. Crassulacean acid metabolism (CAM)Cacti, pineapple, vanilla, agave and maturePhalaenopsis. Spatial and temporal Water use efficiency Nocturanl acidification

  19. § 20.3 PentosePhosphatePathway in plants and animal generateNADPH,CO2, and5C sugar. 5C sugar is components of RNA, DNA, ATP, NADH, FAD, CoA.  take place in cytoplasm [gluconeogenesis] G6P dehydrogenase + CO2 isomerase epimerase 35C26C + 13C (p. 579) transaldolase

  20. Oxidative phaseof PPP Phase 1 Glucose 6-P + 2 NADP+ + H2O  ribose 5-P + 2 NADPH + 2 H+ + CO2 C-1 Intramolecular ester C-1 carboxyl group C-5 hydroxyl group

  21. Nonoxidative phaseof PPP transketolaseandtransaldolase (Ex.1)  linked between PPP and glycolysis (2C) TPP -Ketoglutarate dehydrogenase pyruvate dehydrogenase

  22. Transaldolase DHAP (3C) Transketolase

  23. Transketolase: 2C

  24. Transaldolase: 3C C-3 and C-4 is split

  25. Carbanion intermediates formation– the common feature of transketolase and transaldolase

  26. The rate of PPP is controlled bythe level of NADP+ 3 (5C)  2 (6C) + 1 (3C)

  27. § 20.4 The fate of glucose 6-phosphate– the need for NADPH, ribose 5-P, and ATP 5C  NADPH e.g., rapidly dividing cells Net: 5 G6P + ATP  6 R5P + ADP + H+

  28. 5C = NADPH Net: G6P + 2 NADP+ + H2O  R5P + 2 NADPH + 2H+ + CO2

  29. 5C NADPH, G6P  CO2 Net: G6P + 12 NADP+ + 7 H2O  6CO2+ 12 NADPH + 12H+ + Pi The cytoplasm of a live cell from a well-fed rat: NADP+/NADPH≒ 0.014 NAD+/NADH= 700

  30. Both NADPH and ATP are required ATP Net: 3 G6P + 6 NADP+ + 5 NAD+ + 5 Pi + 8 ADP  5 pyruvate + 3 CO2+ 6 NADPH + 8H+ + 5 NADH + 2 H2O + 8 ATP

  31. Calvin cycle: CO2 fixation to use NADPH C6 + C3 C5 in regeneration phase PPP: CO2 production to produce NADPH C5  C6 + C3

  32. Reactive oxygen species removed superoxide dismutase (p. 518) catalase peroxidase (glutathione, ascorbate) G6P dehydrogenase reduced glutathione (GSH)GSSG reduced ascorbate G6P dehydrogenase level   [NADPH]   sensitive to oxidative stress especially important in red blood cells Phytochelatin (-Glu-Cys)n-Gly n= 2~7

  33. The functions ofreduced glutathione (GSH)  Serves as a sulfhydryl buffer maintains the cysteine residues of hemoglobin and other red-blood-cell proteins in the reduced state. in normal red blood cells: [GSH]/[GSSG]  500 To maintain the normal structural of red blood cells To keep hemoglobin in theferrousstate To detoxify hydrogen peroxide and organic peroxides glutathione peroxidase: 2 GSH + ROOH  GSSG + H2O + ROH § How to regenerate GSH mediate glutathione reductase – a flavoprotein NADPH FAD-Enz (FADH2-Enz)  Enz-cys-cys-Enz (Enz-cys-SH)  GSSG (GSH)

  34. Glucose 6-phosphate dehydrogenase– plays a key role in protection against ROS Glucose 6-phosphate dehydrogenase deficiency – is inherited on the X chromosome – pamaquine, a purine glycoside of fava beans, leads to the generation of peroxides, then induced hemolytic anemia – urine turned black, jaundice developed, and the hemoglobin content of the blood dropped sharply – cross-linked hemoglobins to form Heinz bodies on cell membrane caused membrane damage and cell lysis

  35. Glucose 6-phosphate dehydrogenase deficiency– not all bad  protect against falciparum malaria  the parasites required GSH and the products of PPP for optimal growth  11% among Americans of African heritage  the interplay of heredity and environment in the production of disease  atypical reactions to drugs may have a genetic basis 瘧疾分為四種，其中，最嚴重的是惡性瘧 （falciparum malaria），這種瘧疾會對生命造成威脅。 其他三種瘧疾--隔日瘧、三日瘧卵圓形瘧疾、(vivax, malariae及ovale)則較不嚴重，並且沒有立即致命的危險。

  36. Fenton reactionfrom plant physiol biochem (2000) 38: 125-140 The exceedingly active oxygen species can be produced in a Fenton reaction involving Cu+ and H2O2 O2＋ AH2 → H2O2＋ A 2 Cu2+＋AH2→ 2 Cu+＋ A ＋ 2 H+ Cu+ ＋H2O2 → Cu2+ ＋ OH ＋ OH-

  37. 96T (191) 97T

  38. 98T 95C The reactions of pentose phosphate pathway operate exclusively in (A) mitochondria, (B) cytoplasm, (C) chloroplast, (D) ribosome, (E) endoplasmic reticulum. 97C

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