natural products 2
TRANSCRIPT
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UPTAKE OF NITROGENBY PLANTS
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THE NITROGEN CYCLE
NitrogenFixingBacteria
N2
AminoAcids
HigherPlants
HigherPlants
NO3- NH3
NO2-
NitrifyingBacteria(Nitrobacter)
NitrifyingBacteria(Nitrosomas)
proteins, nucleic acidselectron carriers,alkaloids
returned tothe soil or the
atmosphere
ETC
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In this section we will study the mechanismsby which plants take up nitrogen.
First, however, we need to look at a couple ofcoenzyme systems.
NAD+ NADH
NADP+ NADPH
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THE NAD+ / NADP+ COENZYMES
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N
NN
NN
CNH
2
O
O
CH2
O P O
O
O
P
O
O
O CH2
O
OH OH
OH O
NH2
R- -
+
NICOTINE ADENINE DINUCLEOTIDE
NAD+
NADP+
R = -H
R = -PO3H
N
CNH
2
O
R+
Natures HydrideReducing / OxidizingCoenzyme (reagent)
membranes
cytosol
The two forms differby a phosphate groupwhich also controls the
location in the cell.
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NAD+ and NADP+ ARE HYDRIDE ACCEPTORS
OXIDATION
N
C
NH2
O
R+
C
O
H
H
C
O
N
C
NH2
O
R
H
:
H
..
hydride transfers
REDUCTION
:B-EnzH-B-Enz
NAD+
NADP+
NADH
NADPH
NADH and NADPH ARE HYDRIDE DONORS
alcohol ketone oraldehyde
Unlike ordinary chemical reagents,these coenzymes function reversibly.
AROMATICBUT
CHARGED
UNCHARGEDBUT NOT
AROMATIC
OXIDATION
REDUCTION
-2e-
+2e-
-2e-
+2e-
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N
CNH
2
O
R+
N
CNH
2
O
R
H
H
..
hydride
acceptor
NAD+
NADP+
NADH
NADPH
Unlike ordinary chemical reagents,these coenzymes function reversibly.AROMATIC
BUTCHARGED
UNCHARGEDBUT NOT
AROMATIC
OXIDATION
REDUCTION
-2e-
+2e-
H:-
BIOCHEMICAL REVERSIBILITY
hydride
donor
Many biochemical reagents aredesigned to reversible -
this is the ultimate in conservation
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C
O
H
H
C
O
NAD+ NADH
BIOCHEMICAL NOTATION
C
O
H
H
C
O
NADH NAD+
oxidation
reduction
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OTHER FUNCTIONAL GROUPS CAN BE OXIDIZED / REDUCED
C
N
H
H
H
C
NH
NADH NAD+
reduction
imine amine
:..
C
NH
N
CNH
2
O
R
HH
..
Enz-B-H
:
This process is one ofthe steps of
REDUCTIVE AMINATION
one of the ways thatplants take upnitrogen.
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REDUCTIVE AMINATION
C O
H3
N:
H-B-Enz
..: C O HNH
H- H2O
N CH
N
CNH
2
O
R
HH
..
NAD+
Enz-B-H
NADH
CNH
H
..
....
aldehydeor ketone
imine
amine
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C
O
RR R C R
NH2
H
NH4+ HCO2
-
DC
N
RR
HH
H C
O
O
+
-....
:
..:
formateion
CLASSICAL REACTION
LEUCKART REACTIONREDUCTIVE AMINATION
ammoniumformate
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HOW PLANTS INCORPORATENITROGEN
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GLUCOSE
GLYCOLY
SIS
.a-ketoglutaric acid
CITRICACID
CYCLE
FORMATION OF AMINO ACIDS
CH2
CH2
C
O
COOHHOOC
NH3
NADH
NAD+
CH2
CH2
C
NH2
COOHHOOC
H
an intermediate from
the citric acid cycle
a-ketoglutaric acid
glutamic acid
(NO3-)PRIMARY
METABOLISM
Glutamic acid is the only amino acidthat can be formed by direct uptakeof nitrogen from the soil.
Other amino acids are formed by
transamination.
REDUCTIVE AMINATION
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CH C
OH
R1
O
NH2
CH C
OH
R2
O
NH2
C C
OH
R1
O O
C C
OH
R2
O O
+ +PLP
glutamic acid or
other a-amino acid
NITROGEN EXCHANGETRANSAMINATION
transaminaseenzyme
Most other amino acids are formed by using the -NH2 groupsfrom glutamic acid in transamination reactions.
However, any amino acid can subsequently transfer its amino
group to an a-ketoacid to form a new amino acid.
a-ketoacid
Plants have a severe need for nitrogen and they practice asmuch conservation as possible. Nitrogen is transferred towhere it is needed most.
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CH2
CH2
C COOHHOOC
O
CH2
C
O
COOH
CH3
C
O
COOH
phenylpyruvic acid
pyruvic acid
a-ketoglutaric acid
phenylalanine
CH3
C
NH2
COOH
H
alanine
CH2
C
NH2
COOH
H
CH2
CH2
C
NH2
COOHHOOC
H
glutamic acid
glutamicacid
a-ketoglutaricacid
phenyl-alanine
phenyl-pyruvic acid
alanine pyruvicacid
SOME TRANSAMINATIONS
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FOR MANY OF THE a-AMINO ACIDS FOUND IN NATURETHERE IS A CORRESPONDING a-KETOACID*
alanine pyruvic acid
phenylalanine phenylpyruvic acid
glutamic acid a-ketoglutaric acid
* Some amino acids are made by dimerizations or other non-direct pathways.
valine
leucinea-ketovaleric acid
tyrosine p-hydroxyphenylpyruvic acid
a-ketohexanoic acid
a-amino acid a-keto acid
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CARBAMOYL PHOSPHATE
A Second Method of Transamination
In some plants the major method of nitrogen uptake utilizescarbamoyl phosphate.
NH2
C
O
O P
O
O
OHCO2 + NH4+ + 2 ATP + H2O + 2 ADP + Pi
carbamoyl phosphate
NH2
C
O
O P
O
O
OH
C
O
COOH
.. :Nu C
O
COOH
NH2
H
+ O=C=O
+ Nu-PO3H
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FAD - ANOTHER COENZYME
A Return to Modification of Amino Acids
Process 4
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AMINO ACID METABOLISMWHAT A PLANT CAN DO TO AMINO ACIDS
R CH2
CH
NH2
COOH
R CH2
C
O
HR CH2 C
O
COOH
R CH2
CH2
NH2
C CH
H
R
COOH
1 2
3 4
oxidativedeamination
decarboxylation
oxidative
deamination
decarboxylation deamination
[O]-NH3
[O]-NH3-CO2
-CO2-NH3
Processes 1 2 3 use PLP, pyridoxyl-5-phosphate (B6) coenzymeProcess 4 uses FAD, flavine adenine dinucleotide (B2) coenzyme
and the coenzyme NADH (both discussed later)
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FLAVINE ADENINE DINUCLEOTIDE
N
NN
N
NH2
NH
N
N
NO
O
CH2
CH3
CH3
CH CH CH CH2
O
OHOHOH
P OOH
O
P OOH
O
CH2 O
OH OH
Flavine adenine dinucleotideFAD ( Vitamin B2 )
Cofactor = Mg+2
4
NH
N
N
NO
O
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NH
N
N
NO
O
NH
N
N
NO
O H
H
2e- + 2 H+ +
FAD FADH2
THIS TOO IS A REVERSIBLE COENZYME
It is usually associated with the family of enzymes calledamine oxidases.
R CH2
CH
NH2
COOH
R CH2
C
NH
COOH
R CH2
C
O
COOH
FAD FADH2
amineoxidase
H2O
hydrolysis
imine
a-ketoacid
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POSSIBLE CHEMICAL SEQUENCE FOR DEAMINASES
R CH2
CH
NH2
COOH
R CH2
C
NH
COOH
R CH2
C
O
COOH
FAD FADH2
amineoxidase
H2O
hydrolysis
imine
a-ketoacid
NADH
NAD+
R C C
COOH
O
H
H
H
H
C C
COOH
R H
H
- H2O
dehydration
a,b-unsaturatedacid
a-hydroxyacid
conversion of anamino acid to ana,b-unsaturated
acid
4
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THE MECHANISM FOR FAD OXIDATIONS ANDREDUCTIONS IS NOT COMPLETELY KNOWN
1. It may be a radical-like process involving one-electron transfers.
2. A hypothetical ionic mechanism (mine, not proven) can also be formulated:
NH
N
N
NO
O
C
R
NH2
COOH
H..
NH
N
N
NO
OH
N H
R COOH
H
H
..
Enz-BH
NH
N
N
NO
HOH
..CR COOH
N
HH
+
Enz-B:
CR COOH
NH
NH
N
N
NO
O H
H
+
..
....
Enz-BH
..
..
..
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AMINE OXIDASES
Monoamine Oxidases (MAO)
Diamine Oxidases
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Two types of amine oxidases are common:
Monoamine oxidases and Diamine Oxidases
NH2
COOH
C O
COOH
NH2
NH2
COOH
NH2
O
HCOOH
Monoamine
Diamine
AMINE OXIDASES
.. well see more of this later
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BIOLOGICAL COENZYMES
A Table of Coenzyme Function for Future Reference
The coenzymes are natures chemical reagents and eachhas tis own specific reactions that it can carry out.
Amazingly, nature uses very few coenzymes to carry outthe majority of its chemical transformations.
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COENZYMES - 1
Pyridoxyl-5-phosphate MODIFIES AMINO ACIDS
1) Oxidative deamination to a-ketoacids2) Transaminations3) Oxidative deamination-decarboxylation
to aldehydes4) Decarboxylation to amines
Flavine adenine dinucleotide 1) oxidation of amines to imines(amine oxidases)
2) oxidation of hydrocarbons( alkanes to alkenes )
S-Adenosylmethionine1) Biological methylation reagent for
alcohols, phenols, amines
Nicotine Adenine Dinucleotide
1) Reduction of C=O2) Oxidation of -CH-OH
PLP (P5P)
FAD / FADH2
SAM (SAdM)
NAD / NADP
NADH / NADPH
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COENZYMES - 2
Adenosine triphosphate
ATP
1) Energy storage2) Modifies alcohols3) Traps alcohols4) Coupled reactions
Coenzyme A
CoA
1) Transfers acyl groups
Biotin 1) Carries / transfers CO2 in theform of -COOH groups
Lipoic Acid 1) Oxidizes acyl groups2) Acyl group transfer
Thiamine pyrophosphate
TPP
1) Formation of acyloins
(a-hydroxyketones)2) Oxidative decarboxylations ofa-ketoacids3) Non-oxidative decarboxylations
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COENZYMES - 3
While not strictly speaking coenzymes, these chemicals also
bring about changes.
1) Hydrolysis2) Hydration
1) Oxidations (hydroxylases) (oxidases)2) Oxidative couplings (phenols)
H2O
O2
Water
Oxygen
This list is not exhaustive, but it includes the majorcoenzymes that we will be discussing.