Chapter 20 the calvin cycle and p entose p hosphate p athway an evolutionary kinship
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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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Chapter 20 the calvin cycle and p entose p hosphate p athway an evolutionary kinship

Chapter 20 The Calvin cycle and Pentose Phosphate Pathway an evolutionary kinship

§ Dark reaction (Calvin cycle)

§ Light reaction (Ch. 19)


Calvin cycle take place in the stroma of chloroplast

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+


R ib u lose 1 5 bis phosphate c arboxylase o xygenase rubisco catalyzes the rate limiting step

Ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) catalyzes the rate-limiting step

G°=  12.4 kcal/mol


Tracing the fate of co 2 c 3 plant

Tracing the fate of CO2(C3 plant)

time course


Rubisco

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?


Chapter 20 the calvin cycle and p entose p hosphate p athway an evolutionary kinship

Taiz and Zeiger, 2006

substrate

active form

Rubisco activase:

exhibit an ATPase activity

two polypeptide (42 and 47 kDa)


Oxygenase activity of rubisco

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


Photorespiration a wasteful process

Photorespiration  a wasteful process

¾ C


Chapter 20 the calvin cycle and p entose p hosphate p athway an evolutionary kinship

TPP


Chapter 20 the calvin cycle and p entose p hosphate p athway an evolutionary kinship

23C

16C + 33C

 35C


Chapter 20 the calvin cycle and p entose p hosphate p athway an evolutionary kinship

5C


Chapter 20 the calvin cycle and p entose p hosphate p athway an evolutionary kinship

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?


Synthesis of sucrose and startch in cytoplasm and chloroplasts separately

Synthesis ofsucroseandstartch in cytoplasm and chloroplasts, separately.

ADP-G starch

Phosphate translocator

(diel)

Storage forms in plants: sucrose, starch, fructan


Chapter 20 the calvin cycle and p entose p hosphate p athway an evolutionary kinship

§ 20.2 The activity of the Calvin cycle depends on

environmental conditions

alkaline pH and [Mg2+]

rhythm phenomenon


Chapter 20 the calvin cycle and p entose p hosphate p athway an evolutionary kinship

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).


Chapter 20 the calvin cycle and p entose p hosphate p athway an evolutionary kinship

Calvin cycle


C 4 pathway of tropical plants sugar cane

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+


Crassulacean acid metabolism cam cacti pineapple vanilla agave and mature phalaenopsis

Crassulacean acid metabolism (CAM)Cacti, pineapple, vanilla, agave and maturePhalaenopsis.

Spatial and temporal

Water use efficiency

Nocturanl acidification


20 3 p entose p hosphate p athway in plants and animal

§ 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


Oxidative phase of ppp

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


Nonoxidative phase of ppp

Nonoxidative phaseof PPP

transketolaseandtransaldolase (Ex.1)

 linked between PPP and glycolysis

(2C)

TPP

-Ketoglutarate dehydrogenase

pyruvate dehydrogenase


Transaldolase

Transaldolase

DHAP

(3C)

Transketolase


Chapter 20 the calvin cycle and p entose p hosphate p athway an evolutionary kinship

Transketolase: 2C


Chapter 20 the calvin cycle and p entose p hosphate p athway an evolutionary kinship

Transaldolase: 3C

C-3 and C-4 is split


Carbanion intermediates formation the common feature of transketolase and transaldolase

Carbanion intermediates formation– the common feature of transketolase and transaldolase


Chapter 20 the calvin cycle and p entose p hosphate p athway an evolutionary kinship

The rate of PPP is controlled bythe level of NADP+

3 (5C)  2 (6C) + 1 (3C)


20 4 the fate of glucose 6 phosphate the need for nadph ribose 5 p and atp

§ 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+


5c nadph

5C = NADPH

Net: G6P + 2 NADP+ + H2O  R5P + 2 NADPH + 2H+ + CO2


5c nadph g6p co 2

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


Both nadph and atp are required

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


Chapter 20 the calvin cycle and p entose p hosphate p athway an evolutionary kinship

Calvin cycle:

CO2 fixation

to use NADPH

C6 + C3 C5 in regeneration phase

PPP:

CO2 production

to produce NADPH

C5  C6 + C3


Reactive oxygen species removed

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


The functions of reduced glutathione gsh

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)


Glucose 6 phosphate dehydrogenase plays a key role in protection against ros

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


Glucose 6 phosphate dehydrogenase deficiency not all bad

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。


Fenton reaction from plant physiol biochem 2000 38 125 140

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-


Chapter 20 the calvin cycle and p entose p hosphate p athway an evolutionary kinship

96T (191)

97T


Chapter 20 the calvin cycle and p entose p hosphate p athway an evolutionary kinship

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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