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
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?


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



23C

16C + 33C

 35C



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


§ 20.2 The activity of the Calvin cycle depends on

environmental conditions

alkaline pH and [Mg2+]

rhythm phenomenon


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).



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



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


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


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-



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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