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LECTURE PRESENTATIONS
For BROCK BIOLOGY OF MICROORGANISMS, THIRTEENTH EDITION
Michael T. Madigan, John M. Martinko, David A. Stahl, David P. Clark
Chapter 13
Phototrophy,
Chemolithotrophy, and
Major Biosyntheses
Lectures by
John Zamora
Middle Tennessee State University
© 2012 Pearson Education, Inc.
I. Phototrophy
•
•
•
•
•
13.1 Photosynthesis
13.2 Chlorophylls and Bacteriochlorophylls
13.3 Carotenoids and Phycobilins
13.4 Anoxygenic Photosynthesis
13.5 Oxygenic Photosynthesis
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13.1 Photosynthesis
• Photosynthesis is the conversion of light energy to
chemical energy
– Phototrophs carry out photosynthesis (Figure 13.1)
– Most phototrophs are also autotrophs
• Photosynthesis requires light-sensitive pigments
called chlorophylls
• Photoautotrophy requires ATP production and CO2
reduction
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Figure 13.1
PHOTOTROPHS
(all use light
as energy source)
Use CO2
Photoautotrophs
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Use organic carbon
Photoheterotrophs
13.1 Photosynthesis
• Photoautotrophy
– Oxidation of H2O produces O2 (oxygenic
photosynthesis; Figure 13.2)
– Oxygen not produced (anoxygenic
photosynsthesis; Figure 13.2)
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Figure 13.2
Phototrophs
Purple and green bacteria
Cyanobacteria, algae, green plants
Oxygenic
Anoxygenic
Reducing power
Carbon
electrons
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Energy
Light
Reducing power
Carbon
Energy
Light
13.2 Chlorophylls and Bacteriochlorophylls
• Organisms must produce some form of
chlorophyll (or bacteriochlorophyll) to be
photosynthetic (Figure 13.3a)
• Chlorophyll is related to porphyrins
• Number of different types of chlorophyll exist
– Different chlorophylls have different absorption
spectra (Figure 13.3b)
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Figure 13.3a
Cyclopentanone
ring
Phytol
Chlorophyll a
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Cyclopentanone
ring
Phytol
Bacteriochlorophyll a
Figure 13.3b
0.9
Chl a
Bchl a
0.8 360
Absorbance
0.7
0.6
805
430
480
0.5
870
680
475
525
0.4
590
0.3
0.2
0.1
340 400
500
600
700
Wavelength (nm)
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800
900
13.2 Chlorophylls and Bacteriochlorophylls
• Cyanobacteria produce chlorophyll a (Figure 13.4)
• Prochlorophytes produce chlorophyll a and b
• Anoxygenic phototrophs produce
bacteriochlorophylls
• Chlorophyll pigments are located within special
membranes
– In eukaryotes, called thylakoids (Figure 13.5)
– In prokaryotes, pigments are integrated into
cytoplasmic membrane
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Figure 13.4
Pigment/Absorption
maxima (in vivo)
Bchl a
(purple bacteria)/
805, 830–890 nm
Bchl b
(purple bacteria)/
835–850, 1020–1040
nm
Bchl c
(green sulfur
bacteria)/745–755
nm
Bchl cS
(green nonsulfur
bacteria)/740 nm
Bchl d
(green sulfur
bacteria)/705–740
nm
Bchl e
aNo
double bond between C3 and
C4; additional H atoms are in
positions C3 and C4.
bP,
Phytyl ester (C20H39O—); F,
farnesyl ester (C15H25O—); Gg,
geranylgeraniol ester (C10H17O—);
S, stearyl alcohol (C18H37O—).
(green sulfur
bacteria)/719–726
nm
cNo
Bchl g
dBacteriochlorophylls
(heliobacteria)/
670, 788 nm
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double bond between C3 and
C4; an additional H atom is in
position C3.
c, d, and e
consist of isomeric mixtures with
the different substituents on R3
as shown.
Figure 13.5
Outer
membrane
Inner membrane
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Stroma
Thylakoid
membrane
Stacked thylakoids
forming grana
13.2 Chlorophylls and Bacteriochlorophylls
• Reaction centers participate directly in the
conversion of light energy to ATP
• Antenna pigments funnel light energy to
reaction centers (Figure 13.6)
• Chlorosomes function as massive antenna
complexes (Figure 13.7)
– Found in green sulfur bacteria and green
nonsulfur bacteria
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Figure 13.6
LHI
LHII
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Reaction
center
Figure 13.7
Bchl c, d, or e
In
BP
FMO
Out
RC
Membrane proteins
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13.3 Carotenoids and Phycobilins
• Phototrophic organisms have accessory pigments
in addition to chlorophyll, including carotenoids and
phycobiliproteins
• Carotenoids (Figure 13.8)
– Always found in phototrophic organisms
– Typically yellow, red, brown, or green (Figure 13.9)
– Energy absorbed by carotenoids can be
transferred to a reaction center
– Prevent photooxidative damage to cells
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Figure 13.8
H3C CH3
CH3
CH3
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H3C
CH3
CH3
CH3
H3C CH3
Figure 13.9
I. Carotenes
Diaponeurosporene
Neurosporene
Lycopene
-Carotene
-Carotene
Chlorobactene
-Isorenieratene
Isorenieratene
II. Xanthophylls
OH-Spheroidenone
Spheroidenone
Spirilloxanthin
Okenone
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Heliobacteria
Purple bacteria
Green nonsulfur bacteria
(Chloroflexus)
Green sulfur bacteria
Purple bacteria
(in presence of air)
Green sulfur bacteria
(brown-colored species)
13.3 Carotenoids and Phycobilins
• Phycobiliproteins are main antenna pigments
of cyanobacteria and red algae
– Form into aggregates within the cell called
phycobilisomes (Figure 13.10)
– Allow cell to capture more light energy than
chlorophyll alone (Figure 13.11)
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Figure 13.10
Allophycocyanin
Phycocyanin
Thylakoid
membrane
Phycocyanin
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Figure 13.11
0.9
0.8
Chlorophyll a
peaks
Absorbance
0.7
0.6
Phycocyanin
peak
0.5
0.4
0.3
0.2
0.1
340 400
500
600
700
Wavelength (nm)
© 2012 Pearson Education, Inc.
800
13.4 Anoxygenic Photosynthesis
• Anoxygenic photosynthesis is found in four phyla
of Bacteria
• Photosynthesis apparatus embedded in
membranes (Figure 13.12)
• Electron transport reactions occur in the reaction
center of anoxygenic phototrophs (Figure 13.13)
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Figure 13.12
Vesicles
Lamellar
membranes
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Figure 13.13
Photosynthetic
membrane
H
M
L
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13.4 Anoxygenic Photosynthesis
• Reducing power for CO2 fixation comes from
reductants present in the environment (i.e., H2S,
Fe2+, or NO2)
– Requires reverse electron transport for NADH
production in purple phototrophs (Figure 13.14)
– Electrons are transported in the membrane
through a series of proteins and cytochromes
(Figure 13.15)
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Figure 13.14
1.0
Strong
electron
donor
0.75
0.5
E0
(V) 0.25
Cyclic electron
flow (generates
proton motive
force)
0.0
0.25
Poor
electron
donor
0.5
Red or infrared light
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External
electron
donors
Figure 13.15
Light
Out
(periplasm)
Quinone
pool
ATPase
Photosynthetic
membrane
In
© 2012 Pearson Education, Inc.
(cytoplasm)
13.4 Anoxygenic Photosynthesis
• For a purple bacterium (Figure 13.16) to grow
autotrophically, the formation of ATP is not
enough
– Reducing power (NADH) is also necessary
– Reduced substances such as H2S are
oxidized and the electrons eventually end up
in the “quinone pool” of the photosynthetic
membrane (Figure 13.17)
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Figure 13.16
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Figure 13.17
Purple bacteria
Green sulfur bacteria
Heliobacteria
1.25
1.0
0.75
0.5
E0 (V)
0.25
0
Reverse
electron
flow
0.25
0.5
Light
Light
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Light
13.5 Oxygenic Photosynthesis
• Oxygenic phototrophs use light to generate ATP
and NADPH
• The two light reactions are called photosystem I
and photosystem II
• “Z scheme” of photosynthesis (Figure 13.18)
– Photosystem II transfers energy to photosystem I
• ATP can also be produced by cyclic
photophosphorylation
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Figure 13.18
1.25
The Z Scheme:
1.0
PSII PSI
0.75
Cyclic electron
flow (generates
proton motive
force)
0.5
0.25
E0
0.0
(V)
0.25
Noncyclic
electron flow
(generates
proton motive
force)
Light
0.5
Photosystem I
0.75
1.0
Photosystem II
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Light
II. Chemolithotrophy
•
•
•
•
•
•
13.6 The Energetics of Chemolithotrophy
13.7 Hydrogen Oxidation
13.8 Oxidation of Reduced Sulfur Compounds
13.9 Iron Oxidation
13.10 Nitrification
13.11 Anammox
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13.6 The Energetics of Chemolithotrophy
• Chemolithotrophs are organisms that obtain
energy from the oxidation of inorganic
compounds
• Mixotrophs are chemolithotrophs that require
organic carbon as a carbon source
• Many sources of reduced molecules exist in
the environment
• The oxidation of different reduced compounds
yields varying amounts of energy
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13.7 Hydrogen Oxidation
• Anaerobic H2-oxidizing Bacteria and Archaea
are known
• Catalyzed by hydrogenase
• Calvin cycle and hydrogenase enzymes allow
chemolithotrophic growth (Figure 13.20)
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Figure 13.20
Membrane-integrated
hydrogenase
Out
In
Cytoplasmic
hydrogenase
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Cell material
13.8 Oxidation of Reduced Sulfur
Compounds
• Many reduced sulfur compounds are used as
electron donors (Figure 13.22a)
• Discovered by Sergei Winogradsky
• H2S, S0, S2O3 are commonly used
• One product of sulfur oxidation is H+, which lowers
of the pH of its surroundings
• Sox system oxidizes reduced sulfur compounds
directly to sulfate
• Usually aerobic, but some organisms can use
nitrate as an electron acceptor
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Figure 13.22a
Electron
transport
Sox
system
APS reductase
sulfide
Electron
transport
Adenosine
phosphosulfate
(APS)
sulfur
thiosulfate
sulfite
sulfate
Sulfite
oxidase
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Substrate-level
phosphorylation
13.8 Oxidation of Reduced Sulfur
Compounds
• Electrons from reduced sulfur compounds
reach the electron transport system (Figure
13.22b)
– Transported through the chain to O2
– Generates a proton motive force that leads to
ATP synthesis by ATPase
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Figure 13.22b
Out
Reverse e flow
In
Cell
material
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13.9 Iron Oxidation
• Ferrous iron (Fe2+) oxidized to ferric iron
(Fe3+)
• Ferric hydroxide precipitates in water
• Many Fe oxidizers can grow at pH < 1
– Often associated with acidic pollution from
coal mining activities (Figure 13.23)
• Some anoxygenic phototrophs can oxidize
Fe2+ anaerobically using Fe2+ as an electron
donor for CO2 reduction
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Figure 13.23
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13.9 Iron Oxidation
• Ferrous iron oxidation begins in the
periplasm, where rusticyanin oxidizes Fe2+ to
Fe3+ (Figure 13.24)
• Rusticyanin then reduces cytochrome c, and
this subsequently reduces cytochrome a
• Cytochrome a interacts with O2 to form H2O
• ATP is synthesized from ATPases in the
membrane
• Autotrophy in Acidithiobacillus ferrooxidans is
driven by the Calvin cycle
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Figure 13.24
Out
(pH 2)
Outer membrane cyt c
Rusticyanin
Reverse e flow
In
(pH 6)
Cell material
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13.9 Iron Oxidation
• Ferrous iron can be oxidized under anoxic
conditions by certain anoxygenic phototrophic
bacteria (Figure 13.25)
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Figure 13.25
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13.10 Nitrification
• NH3 and NO2 are oxidized by nitrifying
bacteria during the process of nitrification
• Two groups of bacteria work in concert to fully
oxidize ammonia to nitrate
• Key enzymes are ammonia monooxygenase,
hydroxylamine oxidoreductase, and nitrite
oxidoreductase
• Only small energy yields from this reaction
– Growth of nitrifying bacteria is very slow
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13.10 Nitrification
• Ammonia-oxidizing bacteria (Figure 13.26)
– NH3 is oxidized by ammonia monooxygenase
producing NH2OH and H2O
– Hydroxylamine oxidoreductase then oxidizes
NH2OH to NO2
– Electrons and protons used to generate ATP
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Figure 13.26
Oxidation of
hydroxylamine
Out
In
Oxidation of
ammonia
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Reduction
of oxygen
13.10 Nitrification
• Nitrite-oxidizing bacteria (Figure 13.27)
– Nitrite (NO2) is oxidized by enzyme nitrite
oxidoreductase to nitrate (NO3)
– Electrons and protons used to generate ATP
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Figure 13.27
Periplasm
Reverse e flow
to make NADH
Cytoplasm
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Oxidation
of nitrite
Reduction
of oxygen
13.11 Anammox
• Anammox: anoxic ammonia oxidation
– Performed by unusual group of obligate
aerobes (Figure 13.28a and b)
– Anammoxosome is compartment where
anammox reactions occur (Figure 13.28c)
• Protects cell from reactions occurring during
anammox
• Hydrazine is an intermediate of anammox
• Anammox is very beneficial in the treatment of
sewage and wastewater
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Figure 13.28a
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Figure 13.28b
Anammoxosome
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Figure 13.28c
Anammoxosome
membrane
Out
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In
Electron
transport
III. Major Biosyntheses: Autotrophy and
Nitrogen Fixation
•
•
•
•
13.12 The Calvin Cycle
13.13 Other Autotrophic Pathways in Phototrophs
13.14 Nitrogen Fixation and Nitrogenase
13.15 Genetics and Regulation of Nitrogen
Fixation
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13.12 The Calvin Cycle
• The Calvin cycle (Figure 13.29)
– Named for its discoverer Melvin Calvin
– Fixes CO2 into cellular material for autotrophic
growth
– Requires NADPH, ATP, ribulose bisphophate
carboxylase (RubisCO), and
phosphoribulokinase
– 6 molecules of CO2 are required to make 1
molecule of glucose (Figure 13.30)
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Figure 13.29
Ribulose
bisphosphate
carboxylase
(RubisCO)
Ribulose
bisphosphate
Phosphoglyceric acid
Unstable intermediate
Two phosphoglyceric acid (PGA)
Oxygenation
reaction
1,3-Bisphosphoglyceric acid
Glyceraldehyde 3-phosphate
To biosynthesis
Cycle repeats
starting with (a)
Phosphoribulokinase
Ribulose 5-phosphate
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Ribulose bisphosphate
Figure 13.30
12 3-Phosphoglycerate
(36 carbons)
RubisCO
6 Ribulose
1,5-bisphosphate
(30 carbons)
12 1,3-Bisphosphoglycerate
(36 carbons)
Phosphoribulokinase
12 Glyceraldehyde
3-phosphate
(36 carbons)
6 Ribulose
5-phosphate
(30 carbons)
Sugar
rearrangements
10 Glyceraldehyde
3-phosphate
(30 carbons)
Fructose
6-phosphate
(6 carbons)
To biosynthesis
Overall stoichiometry:
6 CO2  12 NADPH  18 ATP
 12 NADP  18 ADP  17 Pi
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C6 H12 O6(PO3 H2)
13.13 Other Autotrophic Pathways in
Phototrophs
• Green sulfur bacteria use the reverse citric acid
cycle to fix CO2 (Figure 13.32a)
• Green nonsulfur bacteria use the
hydroxypropionate pathway to fix CO2
(Figure 13.32b)
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Figure 13.32
Cell material
Glyceraldehyde 3-P
Hexose-P
Oxalacetate
Phosphoenolpyruvate
Malate
Fumarate
Pyruvate
Succinate
Ferredoxinred
Succinyl-CoA
Ferredoxinred
Acetyl-CoA
Citrate
-Ketoglutarate
Net reaction:
Isocitrate
3 CO2  12 H  5 ATP
C3H6O3PO32  3 H2O
Cell material
(Acetyl-CoA)
Malyl-CoA
(Hydroxypropionyl-CoA)
Glyoxylate
Succinyl-CoA
Net reaction:
2 CO2  4 H  3 ATP
(Propionyl-CoA)
(Methylmalonyl-CoA)
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C2H2O3  H2O
13.14 Nitrogenase and Nitrogen Fixation
• Only certain prokaryotes can fix nitrogen
• Some nitrogen fixers are free-living and
others are symbiotic
• Reaction is catalyzed by nitrogenase
– Sensitive to the presence of oxygen
• A wide variety of nitrogenases use different
metal cofactors (Figure 13.33)
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Figure 13.33
Protein
Homocitrate
Protein
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13.14 Nitrogenase and Nitrogen Fixation
• Electron Flow in Nitrogen Fixation (Figure 13.34)
– Electron donor  dinitrogenase reductase 
dinitrogenase  N2
– Ammonia is the final product
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Figure 13.34
Pyruvate
Electron
flow to
nitrogenase
Pyruvate flavodoxin
oxidoreductase
Flavodoxin
(Oxidized)
Flavodoxin
(Reduced)
Dinitrogenase
reductase
(Reduced)
Dinitrogenase
reductase
(Oxidized)
Dinitrogenase
(Oxidized)
Dinitrogenase
(Reduced)
Nitrogenase
enzyme
complex
N2
reduction
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13.14 Nitrogenase and Nitrogen Fixation
• Unique nitrogenase of Streptomyces
thermoautotrophicus (Figure 13.36)
– A structurally and functionally novel
molybdenum nitrogenase
– S. thermoautotrophicus nitrogenase is
completely insensitive to O2
• Nitrogenase activity can be assayed using
the acetylene reduction assay (Figure 13.37)
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Figure 13.36
Mo
Mo
Superoxide
formation
CO dehydrogenase
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Nitrogenase
Figure 13.37
Atmosphere, 10% C2H2 in air (aerobes) or
10% C2H2 in H2 or Ar (anaerobes)
Acetylene Ethylene
Chart recorder for
gas chromatograph
C2H2
Stoppered vial containing
cell suspension
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Sample headspace
periodically and inject
into gas chromatograph
C2H4
C2H2
C2H4
Nitrogenase
Incubation
C2H2
Time 0
1h
2h
13.15 Genetics and Regulation of
Nitrogen Fixation
• Highly regulated process because it is such an
energy- demanding process
• nif regulon coordinates regulation of genes
essential to nitrogen fixation (Figure 13.38)
• Oxygen and ammonia are the two main
regulatory effectors
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Figure 13.38
Nitrogenase
proteins
Dinitrogenase
reductase
FeMo-co
synthesis
FeMo-co
synthesis
Denitrogenase
reductase
processing
Regulators
Mo
processing
Positive Negative
Flavodoxin
Dinitrogenase
Homocitrate
synthesis
FeMo-co
synthesis

Electron
transport

Pyruvate
flavodoxin
oxidoreductase
FeMo-co
insertion into
dinitrogenase
Metal center
biosynthesis
nif DNA
Q
B
A
L
F
M Z W V S U
X
N
E
Y
T
K
D
H
J
RNA
© 2012 Pearson Education, Inc.