Methanotrophy

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Methanotrophy
Methane ---gt methanol ---gt formaldehyde
Formaldehyde
Ribulose monophosphate pathway
Serine pathway
2-PG
GAP
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Methanol dehydrogenase
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PQQ ---gt cytochrome cL ---gt cytochrome cH
Cyctochrome cH ---gt cytochrome c oxidase ---gt O2
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Formaldehyde assimilation Ribulose monophosphate
pathway
3 Ru5P 3 Formaldehyde
3 Hu6P
C7 C3 2 C5
C4 C3 C7
3 F6P
C6 C3 C4 C5
C3 C3 C6
4 GAP 2 DHAP
3 GAP 2 DHAP
3 formaldehyde ATP GAP ADP
1 GAP
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Formaldehyde assimilation Serine pathway
Net rxn
2 formaldehyde CO2 2 ATP NADH FAD ----gt
2-phosphoglycerate NAD FADH2 2 ADP
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Serine Hydroxymethyl Transferase
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Nitrogen cycles
Nitrate/nitrite Reductase
Ammonia monooxygenase Hydroxylamine oxidoreductase
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N2 3H2 ---gt 2NH3 ?Gº -33.5 kJ/mol
-3
0
However, N-N triple bond is a significant kinetic
barrier
Bond energy 930 kJ/mol
Nitrogen is fixed by anaerobic bacteria
N2 10 H 8 e- 16 ATP ---gt 2 NH4 16 ADP
16 Pi H2
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FeMo Cofactor
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Proposed mechanism for dinitrogen reduction
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Nitrateferredoxin reductase
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Dissimilatory/Respiratory Nitrite Reductase
Siroheme and ferredoxin dependent looks and
behaves a lot like cytochrome c oxidase
NO2- ----gt NO ----gt NH2OH ----gt NH4
3
-3
1
-1
Allows anaerobic organisms to respire electrons
onto nitrite instead of oxygen
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Dissimilatory Nitrite Reductase
NO2- ----gt NO
Nitrite reductase, multicopper enzyme
2
3
NO ---gt N2O
Nitric oxide reductase, heme dependent
2
1
N2O ---gt N2
Nitrous oxide reductase, multicopper enzyme
1
0
Produces NO and N2O - potent greenhouse gasses
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Biological Nitrification
NH3 ---gt NO2- ---gt NO3-
3
5
-3
NH3 O2 2 e- 2 H ---gt NH2OH H2O
Ammonia monooxygenase (related to methane
monooxygenase)
NO2- ---gt NO3- is non-enzymatic
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Hydroxylamine oxidoreductase (heme dependent)
NH2OH H2O ---gt NO2- 5 H 4 e-
2 of these electrons are transferred to
cytochrome bc1
Ultimately they land on O2 and generate proton
gradient
2 electrons are returned to AMO to complete the
cycle
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Assimilation of ammonia
Use glutamate and glutamine as reservoirs
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Glutamine synthase
glutamate NH4 ATP ---gt glutamine ADP Pi
H
Glutamate synthase
glutamine ?KG NADPH H ---gt 2glutamate
NADP
Net reaction
?KG NADPH NH4 ATP ---gt glutamate NADP
H2O ADP Pi
Need catalytic amounts of glutamate! There has to
be another way!
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Glutamine synthase
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Glutamate synthase
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What about the reverse reaction of glutamate
dehydrogenase?
glutamate NADP H2O ---gt ?KG NH4 NADPH
Normally this reaction favors the right
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Glutamine synthetase is a control point for
growth. Many end products allosterically regulate
its activity
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Amino transferases
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Carbamoylphosphate synthase step 1
Bicarbonate
Carbonic phosphoric anhydride
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Carbamoylphosphate synthase step 2
Carbonic phosphoric anhydride
Carbamate
Carbamoylphosphate
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Ornithine transcarbamoylase
Pi
Citrulline
Ornithine
These are ?-amino acids
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Argininosuccinate synthase step 1
Citrulline
Citrullyl-AMP
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Argininosuccinate synthase step 2
Citrullyl-AMP
Argininosuccinate
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Argininosuccinate lyase
Fumarate
Argininosuccinate
Arginine
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Arginase
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The aspartate/malate shuttle
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In respiration asp/mal shuttle
Moves NADH into the mitochondrion with net
movement of one H in but also moves NH3 out!
For every asp out a mal goes in and NH3 is moved
out to cytoplasm