Download Biosynthesis of Phenylpropane

Biosynthesis of Phenylpropane
David Wang’s Wood Components Synthesis’s Class
Phenylpropane
n
Phenylpropane derivatives are compounds composed of a
C6-C3 carbon skeleton comprised of an aromatic ring with
a propane side chain.
n
Phenylpropanoids are considered to be essential for plant
life.
n
Dehydrodiconiferyl alcohol glucoside: dividing plant cells and acts
as a cytokinin.
n
Flavonoid : polar transportation of auxin.
n
Flavonoids pigments: protect growing meristems against UV.
n
Isofavonoids and furanocoumarine: antibiotic and phytoalexin and
protect plants from diseases.
Lignin
n Lignin
is the second abundant and important
organic substance in the plant world.
n The
incorporation of lignin into the cell walls of
plants gave them the chance to conquer the Earth’s
land surface.
n Lignin
increased the mechanical strength properties
to such an extent that huge plants such as trees
with heights of even more than 100 m can remain
upright.
Outline of the
Biosynthetic
Pathway of
Phenylpropanoids
Phenylpropanoid pathway
n
Shikimate pathway commonly involved in the biosynthesis of
many aromatic compounds.
n
Biosynthesis of phenylalanine and tyrosine.
n
General phenylprpanoid pathway to afford 4-coumaroyl-Co-A.
n
Pathways for lignin and lignans etc. associated with general
phenylpropanoid pathway.
General Biosynthesis Pathway of Plant Phenolic compounds
Acetyl-CoA
Malonic acid pathway
Phenolic compounds
(C6-C3-C6)n
C6-C3-C6
D-erythose 4-phosphate
Shikimate
pathway
Cinnamate
pathway
C6-C1
C6-C3
(C6-C3)2
(C6-C3)n
L-Phenylalanine
Cinnamic acid
Phosphoenol pyruvic acid
Hydrolysable tannins
Gallic acid
1. Shikimate pathway
phosphoenol pyruvic acid
3-dehydroquinic acid
D-erythrose
4-phosphate
3-deoxy-D-arabino-heptulosonic
acid 7-phosphate
NADP-linked shikimate
dehydrogenase
phosphochorismic acid
shikimic acid
3-dehydroshikimic acid
(1)
phosphorylated
phenylpyruvic acid
苯丙胺酸 arogenic acid
chorismic acid
prephenic acid
p-hydroxyphenylpyruvic acid
Enzyme System in Aromatic Biosynthesis
酪氨酸 Branched Shikimate Pathway Leading to L-Phenylalanine
and L-Tyrosine via Chorismic Acid
Diversity of the Shikimate Pathway
n
The enzyme system in the shikimate pathway is diverse.
This diversity could be cause by:
n
Enzyme organization
n
Localization of enzymes
n
Regulation mechanism of enzymes
n
Occurrence of isozymes
n
Biosynthetic pathways via the metabolic grid.
Diversity of the Shikimate Pathway –
Enzyme organization
n
It is interesting to know whether a series of enzyms in a
certain biosynthetic pathway is located at random in cells
or in a certain order as multienzyme complexes.
n
Multienzyme complexes could be further classified into
mutifunctional polypeptide chains, oligomer enzymes, and
complexes with components of cell organelles.
n
One enzyme catalyzes the reaction in steps three and four
in plants.
Diversity of the Shikimate Pathway –
Localization of enzymes
n
All enzymes involved in the shikimate pathway are located in
chloroplasts or plastids in plants.
n
Chloroplasts are one of the sites where aromatic amino acids
are synthesized → genes of four enzymes in the shikimate
pathway have been found to have transit peptides for
chloroplasts.
n
It has not been elucidated whether or not another shikimate
pathway is involved in the cytoplasm.
Diversity of the Shikimate Pathway – Regulation Mechanism
of Enzyme
n
It has been found that some isoenzymes in
plants are affected by a feedback inhibition,
but others are not affected, and the mode
of gene expression by external stimuli is
different.
n
When tryptophan is excessively formed in
cells the mutase in step 8 is activated, and
the pathway is switched to biosynthesis of
phenylalanine and tyrosine. When the
level of phenylalanine and tyrosine
increases, the reaction in steps 14 and 15
are inhibited, leading to enhanced level of
agrogenic acid, and a termination of the
reaction in step 11.
Diversity of the Shikimate Pathway –
Occurrence of Isoenzymes
n
Isoenzymes are present in the cytoplasm and plastides in
plants, and found on 1 to 4 copies of genes encoding the
enzymes in each step have been found in the genome.
n
The physiological function of these isoenzymes in not know,
but specialization of the isoenzymes for the synthesis of
aromatic amino acids for proteins, or secondary metabolites
has been suggested.
Diversity of the Shikimate Pathway –
Biosynthetic Pathway via Metabolite grid
O
H
I
Y
Z
P
Q
J
K
Plants and microorganisms have specific
channeling for the synthesis of phenylalanine
and tyrosine. It is interesting to note, in
relation to plant evolution, that blue-green
algae have a plant-type channeling and that
B
A
C
plant plastids, which may be derived from the
blue-green algae, have the enzymes system
involved in the shikimate pathway.
Biosynthesis of Lignin
n
Lignin monomers, or monolignols, are produced intracellularly,
then exported to the cell wall, and subsequently polymerized.
n
The monolignols are products of the phenylpropanoid
pathway, starting from phenylalanine, and most of the genes
involved in monolignol production have been cloned or are
present in expressed sequence tag/genomic databases.
Biosynthesis of Lignin
n
The hydroxylation and methylation reactions that ultimately
determine the monomeric composition of lignin (because the
three monolignols differ only in their degree of methoxylation)
have long been considered to occur at the level of the cinnamic
acids.
n
Several experiments have demonstrated that the methylation
steps can also take place at the hydroxycinnamoyl-CoA level,
mediated by either caffeic acid/5-hydroxyferulic acid Omethyltransferase (COMT) or caffeoyl- CoA O-methyltransferase
(CCoAOMT).
Biosynthesis of Lignin
n
Recent work based on radiotracer and in vitro enzyme assays
has shown that the hydroxylation and methylation reactions
occur preferentially at the cinnamaldehyde and cinnamyl
alcohol level in reactions catalyzed by ferulic acid 5hydroxylase (F5H; also named coniferaldehyde 5-hydroxylase
or Cald5H) and COMT (alternatively called 5hydroxyconiferaldehyde O-methyltransferase or AldOMT).
n
COMT preferentially methylates caffeyl aldehyde, 5hydroxyconiferaldehyde, and 5-hydroxyconiferyl alcohol,
although differences exist between the COMTs of different
Biosynthesis of Lignin
n
Traditionally, sinapic acid was thought to be a lignin precursor that was
converted to sinapoyl-CoA by 4CL. However, results of in vitro
experiments with 4CLs from different plants throw significant doubt on
this assumption. Whereas 4CL isoforms from some plants have been
found to convert sinapic acid to sinapoyl-CoA enzymes from other
plants apparently are deficient in this activity.
n
Small differences between 4CL isoforms can significantly influence its
activity.
n
Recently, a model based on structural data postulates that the
substrate specificity of 4CL is determined by 12 amino acid residues.
General Phenylpropanoids Pathway
n
The pathway derived from L-phenylalanine to phenylpropanoids is a
biosynthetic pathway specific to vascular plants.
General Phenylpropanoids Pathway
n
n
The phenylpropanois pathway involves three enzymes:
q
Phenylalanine ammonia-lyase (PAL)
q
Cinnamate 4-hydroxylase (C4H)
q
4-coumarate:CoA ligase (4CL)
Reasons for above three enzymes are distinguished from other enzymes:
q
The reaction are common pathway in the biosynthesis of various
phenylpropanoids.
q
They are induced by UV irradiation or fungal elicitors.
q
The microsome fraction contains all activities to convert phenylalanine to 4coumaric acid.
q
These enzymes seem to be regulated by a common gene regulation
mechanism.
Phenylalanine Ammonia-Lyase
n
Phenylalanine ammonia-lyase (PAL) and tysosine ammonialyase (TAL) which cause formation of phenylpropanoids from
aromatic amino acids.
n
TAL occurs mainly in grasses, and initially through to be a
different enzyme from PAL.
n
Purified enzymes from maize and yeast have been shown to
be single enzymes that have common catalytic sites for Lphenylalanine and L-tyrosine.
Phenylalanine Ammonia-Lyase
n
PAL is distributed in clubmosses, ferns, and seed plants, but does not
occur in mosses and horsetails.
n
The pro-3S proton and amino group of L-phenylalanine and transeliminated to afford trans-cinnamic acid.
n
L-phenylalanine
is first connected to the methylene group of a
dehydroalanine residue at the active center of PAL. trans-cinnamic
acid in then released, and finally the amoino-enzyme complexes
hydrolyzed to give ammonia.
Cinnamate 4-Hydroxylase (C4H)
n
The aromatic ring of cinnamic acid derived from
phenylalanine is hydroxylated.
n
Trans cinnamate 4-monioxygenase catalyzes
hydroxylation of the C4 of cinnamic acid in the presence of
O2 and NADPH. (The product is 4-coumaric acid)
n
Upon hydroxylation proton at C4 is transferred to C3. This
transfer is called NIH shift and suggested to occur via an
oxenoid intermediate.
oxenoid intermediate
Cinnamate 4-Hydroxylase (C4H)
n
Cinnamate 4-hydroxylase is widely distributed in the
microsome fraction of higher plants.
n
The hydroxylase is a multienzyme complex belonging to
cytochrome P450 monooxygenase.
n
The enzyme is located from the surface to the inner site of
the ER membrane, and consists of cytochrome P450 as the
terminal oxidase (hemoprotein) and NADPH-cytochrome
P450 reductase.
維生素B2在組織中可被合成磷酸酯，而形成兩種輔
脢，一為單核酸黃素(Flavine Mononucleotide-FMN)及雙核酸腺嘌呤黃素(Flavine-adenine
dinucleotide--FAD)。此兩種輔脢可形成許多不同脢
系統的不足處，故有彌補群脢之稱。此群脢亦叫做
黃素蛋白(Flavoprotein)，主要涉及氫離子的傳輸，
亦即是電子傳輸的作用。D-胺基酸的氧化脢為
FAD，而L-胺基酸的氧化脢為FMN，但較特別的甘
胺酸的去氫脢為FAD。
Cinnamate 4-Hydroxylase (C4H)
n
It has been shown that only C4H is bound to the ER
membrane in the enzymes of the cinnamate pathway.
n
The activities of C4H with respect to combination with lauric
acid, β-pinene, nerol, in the microsomal fraction can be
separated from that those with respect to cinnamic acid.
n
A full-length open reading frame of 1515 bp, encoding a
P450 protein of 505 residues, was identified and sequenced.
4-Coumarate:Coenzyme A Ligase (4CL)
n
In the conversion of 4-coumarate to flavonoids or lignin,
the carboxyl group of the acid should be activated.
n
The coenzyme A (CoA) thioester of 4-coumaric acid (4Courmarate:CoA ligase, 4CL) is the activated
intermediate.
n
4CL catalyzes the reaction, requires ATP, CoA, and Mg2+,
cinnamate derivatives are converted to the corresponding
CoA ester via AMP-cinnamate derivatives
Formation of Feruloyl-CoA from Ferulic Acid
by Mediation of CoA ligase
4-Coumarate:Coenzyme A Ligase
(4CL)
n Generally,
trans forms of cinnamates are preferable as
substrates.
n 4-coumarate
and CoA as substrates, and AMP as
product inhibit the enzyme reaction depending on their
concentrations.
n 4CL
is distributed in various higher plants, especially in
young stems.
n Isozymes
Lignin Synthesis - Lignin Precursors and Aromatic
Constituents
Lignin Synthesis – Softwood Lignin
n
Softwood lignin is an
aromatic polymer in which
the monomeric
guaiacylpropane units are
the major components
(>90%) and are connected
by both ether and carboncarbon linkage
Lignin Synthesis – Softwood Lignin
Lignin Synthesis – Hardwood Lignin and Grass
lignin
n
Hardwood lignin is composed of guaiacyl and
syringylpropane units connected by linkages similar to
those found in conifer lignin; the ratio of the syringyl unit to
the guaiacyl unit is different among species.
n
Grass lignin is composed of guaiacyl-, syringyl-, and phydroxyphenylpropane units also connected by similar
linkages to those found in conifer lignin.
n
p-Coumaric acid (5-10% of lignin) is mostly esterified at γ-position of
the propyl side chains but is also partly etherified in the lignin.
Lignin-Carbohydrate Bonds
n
The possible existence of covalent bonds between lignin and
polysaccharides has been a subject of much debate and intensive
studies.
n
It is obviously and now generally accepted that such chemical
bonds must exist, and the term “lignin-carbohydrate complex
(LCC)” is used for the covalently bonded aggregates of this type.
n
Chemical bonds have been reported between lignin and
practically all the hemicellulose constituents (even between lignin
and cellulose). These linkages can be either of ester or ether
type and even glycosidic bonds are possible.
Formation of Monolignols
n
Tracer experiments with isotope-labeled lignin precursors
and the associated enzyme experiments have elucidated
the synthetic pathway for p-hydroxycinnamyl alcohols
such as coniferyl, sinapyl, and p-coumaryl alcohol, which
are direct precursors of lignin.
Formation of Monolignols
n
Hydroxylation of 4-coumarate derivatives
n
Methylation of caffeate derivatives
n
Hydroxylation of ferulic acid
n
Reduction of cinnamate derivatives
Hydroxylation of 4-coumarate
derivatives
n
Phenoloxidases activate
molecular oxygen and hydroxylate
4-coumaric acid to caffiec acid.
Methylation of Caffeate derivatives
n
O-Methyltransferase (OMT) is required for the formation of
guaiacyl and syringyl units of lignin.
n
The C3-hydroxyl group of caffeic acid is methylated to
afford ferulic acid by mediation of OMT using S-adenosyl
methionine as methyl donor.
n
The results suggested an
intinate correlation between the
evolution of lignin and the two
types of OMTs.
n
Some gymnosperms give a
positive Maule reaction, might
have OMTs with higher SA/FA
ratios similar to angiosperm
enzymes.
OMT
n
OMT cDNA have been isolated from alfalfa, maize, and
tabocco.
n
Lignin specific OMT cDNAs of aspen and poplar were also
isolated and characterized from the development xylem
tissue and leaves.
n
A full-length OMT cDNA clone isolated from a poplar leaf
cDNA library was sequenced and the amino acid sequence
was established.
n
The poplar OMT sequence contains one ATP-binding site
(consensus GXGXXG) which may play a role in Sadenosylmethionine binding.
OMT
n
Xylem specific promoter and transcriptional regulatory
sequences for aspen bi-OMT have been investigated.
n
Based on the nucleotide sequence of aspen bi-OMT cDNA, specific
primers, GCTCTAGAGCATGGGTTCAACAGGTGAA and
GTTGGAAGCTTAAGGCCAATAGG, that are adjacent to a full-length
bi-OMT cDNA, were used to amplify a 2.7 kb DNA fragment from
confirmed an exact match of the exon sequences with the cDNA
sequence.
OMT
n
Aspen bi-OMT gene contains four exons, and three introns
between the transcription start site.
n
Within this 1.2 kb promoter region, TATA boxes and the
transcription start site were identified.
n
Base on electrophoreticmobility shift assay on DNA-nuclear
protein binding, three cis-acting regulatory sequences were
identified in this 1.2 kb promoter region.
Hydroxylation of Ferulic Acid
n
For the formation of sinapic acid from ferulic acid, C5 of the
ferulic acid must first be hydroxylated.
n
The enzyme catalyzing this reaction requires molecular
oxygen and NADPH.
n
The enzyme in young poplar twigs is located in the microsomal
fraction and has been shown to be a cytochrome P450dependent monooxygenase.
Hydroxylation of Ferulic Acid
n
FAH1 (fah1) of Arabidopsis
n
In the fah1 mutant, the conversion of ferulic acid to 5-hydroxyferulic
acid in the general phenylpropanoid pathway appears to be locked.
n
As a result, the lignin of the mutant lacks the sinapic acid-derived
components and the syringyl lignin, typical of the wild-type.
n
The rosette of wide-type Arabidopsis appears pale blue-green under
long wave UV light due to the fluorescence of sinapoyl malate in the
leaf epidermis. The fah1 mutant which does not contain sinapoyl
malate in the leaf epidermis appears dark red under the same
conditions.
Reduction of Cinnamate Derivatives
n
It was found by a tracer experiment that ferulic acid is
reduced to coniferyl alcohol via coniferyl aldehyde.
n
Feeding experiments with ferulic and sinapic acids to the
shoots of poplar, cherry, Japanese red pine, and ginkgo
showed that gymnosperms reduce only ferulic acid to
coniferyl aldehyde and alcohol, while angiosperms reduce
both ferulic and sinapic acids to the corresponding aldehyde
and alcohol.
Reduction of Cinnamate Derivatives
n
Ferulic and sinapic acids are reduced to the corresponding
cinnamyl alcohols by successive mediation of three
enzymes:
n
n
4-Coumarate:CoA ligase
n
Cinamoyl-CoA reductase
n
Cinnamyl alcohol dehydrogenase
The above enzymes were first isolated from Salix and
Forsythia, and from cell suspension cultures of Glycine max.
Reduction of Cinnamate Derivatives
n
4-hydroxycinnamoyl-CoAs are reduced to the corresponding
aldehydes by medication of 4-hydroxycinnamoyl-CoA
reductase.
Cinnamoyl-CoA Reductase (CCR)
n
4-Hydroxycinnamoyl-CoA reductase requires NADPH as
hydrogen donor, and the best substrate is feruloyl-CoA
followed by 4-coumaroyl-, sinapoyl-, and 5-hydroxyferuloylCoAs.
n
The enzyme does not activate other aromatic or aliphatic
esters.
n
CCR activity was feedback inhibited by NADPH and CoA.
Cinnamyl Alcohol Dehydrogenase
(CAD)
n
The last step in the formation of 4-hydroxycinnamyl alcohols
in the reduction of 4-hydroxycinnamyl aldehydes to the
corresponding alcohols medicated by cinnamylalcohol
dehydrogenase (CAD).
Pathways to monolignols. The
complete metabolic grid of
reactions is shown. All enzyme
reactions shown with a solid
arrow have been
demonstrated to occur in vitro.
Reactions shown in smaller type
may not occur in vivo. The
reactions shown in green seem
the most likely route to
G lignin in vivo. The reactions in
red represent those reactions
consistent with both in vivo and in
vitro evidence for being involved
specifically in S
lignin biosynthesis. The
intermediate in orange is common
to both G and S lignin pathways.
Proposed principal biosynthetic pathway for the
formation of monolignols in woody angiosperms.
C4H, cinnamate 4-hydroxylase
C3H, 4-coumarate 3-hydroxylase
CCoAOMT, caffeoyl CoA O-methyltransferase
CCR, cinnamoyl-CoA reductase
AldOMT, 5-hydroxyconiferaldehyde Omethyltransferase
SAD, sinapyl alcohol dehydrogenase
CAD, cinnamyl alcohol dehydrogenase.
The predominant pathway for monolignol biosynthesis in xylem cells is outlined in black, with the dark arrows showing the primary
substrates and products and the gray arrows showing the minor substrates and products. The blue shading indicates the pathway that is
conserved between angiosperms and gymnosperms, whereas the green shading indicates the angiosperm-specific pathway. The
enzymes and their abbreviations are as follows: CAD, (hydroxy)cinnamyl alcohol dehydrogenase; CCoAOMT, caffeoyl CoA Omethyltransferase; CCR, (hydroxy)cinnamoyl CoA reductase; C3H, p-coumaroyl shikimate/quinate 3-hydroxylase; C4H, cinnamate 4hydroxylase; 4CL, 4-coumarate CoA ligase; COMT, caffeic acid/5-hydroxyferulic acid O-methyltransferase; F5H/Cald5H, ferulate 5hydroxylase/coniferylaldehyde 5-hydroxylase; PAL, phenylalanine ammonia-lyase; SAD, sinapyl alcohol dehydrogenase.
Major Segments of Phenylpropanoid Metabolism in Vascular
Plants as Currently Understood
A Metabolic Channel Model for Independent
Pathways to G and S Monolignols
Dehydrogenative Polymerization of
Monolignols of Lignins
n
Freudenberg et al., found that conifreyl alcohol is
dehydrogenatively polymerized to a high polymer material
(dehydrogenation polymer, DHP).
n
DHP properties (chemically and spectrometrically) are closely related to
those of conifer lignin.
n
Conifer lignin could be formed by dehydrogenative polymerization of
coniferyl alcohol.
Dehydrogenative Polymerization of
Monolignols of Lignins
n
Freudenberg further showed that radicals of monolignols
formed enzymatically couple in a random fashion to yield
quinone methides, which are converted to various dilignols
by the addition of water or by intramolecular nucleophilic
attack by primary alcohol or quinone groups on the benzyl
carbons.
Dehydrogenative Polymerization of
Monolignols of Lignins
n
The dilignols are further dehydrogenated by the enzyme to
their radicals, which are finally converted to lignin and lignincarbohydrate complexs (LCCs) via radical couplings followed
by nucleophilic attack on the benzyl carbons of the
oiligomeric quinone methides by water, by aliphatic and
phenolic hydroxyl groups of lignols, and by hydroxyl- and
carboxyl groups of sugar residues of cell wall
polysaccharides.
Dehydrogenative Polymerization of
Monolignols of Lignins
n
Higuchi proposed that peroxidase in involved in lignification of
plant tissue.
n
Peroxidase localized in tracheary elements, especially in the
secondary walls, which become heavily.
n
Dehydrogenative polymerization of coniferyl alcohol, localization
of the enzyme in tissues, and response against wounding have
been investigated in detail with tobacco peroxidase.
n
It is now considered that both peroxidase and laccase are
involved in dehydrogenative polymerization of monolignols.
Dehydrogenative Polymerization of
Monolignols of Lignins
n
The origin of H2O2 required for the peroxidase reaction was investigated
using horseradish cell walls and cell walls isolate from Forsythia xylem.
n
It is found that H2O2 is formed in a complex reaction that involves a
dismutation reaction of superoxide radicals (O2.-), generated by the
reduction of O2 with NAD..
n
The NAD. is postulated to be formed via oxidation of NADH, which is
provided by the oxidation of malate with NAD:malate oxidoreductase
bound to the cell wall, by the phenyl radicals generated by an oxidase
reaction of some phenols with a peroxidase-Mn2+ complex.
Dehydrogenative Polymerization of
Monolignols of Lignins
n
The formation of H2O2 is stimulated by various monophenols
and especially by coniferyl alcohol, which indicates that
monophenols could be directly involved in the regulation of
H2O2 required for the dehydrogenation.
n
The occurrence of hydrogen peroxide in lignifying cell walls
cytochemically, and found that peroxidase is actually
involved in lignin biosynthesis.
Structure Differences in Dehydrogenation
Polymers
n
Freudenberg found that the yields of dehydrodiconiferyl
alcohol and dl-pinoresinol were considerably higher than the
yield of guaiacylglycerol-β-coniferyl ether when a coniferyl
alcohol solution is added at once to the peroxidase/H2O2
solution.
n
The yields of guaiacylglycerol-β-coniferyl ether increased
when the substrate was added dropwise over long periods of
time to the enzyme solution.
Differences in Biosynthesis of Lignins between
Tissues and Plants
n
Chemical structure of birch lignin is different in wood fibers and
vessels by UV spectral analyses in situ.
n
A syringyl lignin occurs in the secondary walls of the fibers, whereas a
guaiacyl lignin is present in vessel walls.
n
Chemical differences between protolignin of wheat and
synthetic lignin (DHP) have also been pointed out based on
solid-state 13C-NMR analysis of protolignin derived from
administered 13C-ferulic acid.
Differences in Biosynthesis of Lignins between
Tissues and Plants
n
In pine xylem, p-hydroxyphenyl lignin is formed in the compound
middle lamella and cell corners at an early stage of cell wall
differentiation.
n
Guaiacyl lignin is deposited as a major component in the compound
middle lamella at an early stage and in the secondary walls at a later
stage.
n
The content of condensed guaiacyl lignin is higher in the middle
lamella than in the secondary wall lignin.
n
Syringyl lignin is a minor component of conifer lignin and is formed in
the inner layer of the secondary walls a late stage.
Differences in Biosynthesis of Lignins between
Tissues and Plants
n
It was suggested that lignins in xylem tissue are chemically
heterogeneously, that the lignifications is controlled by the
individual cell, and that the mode of lignin biosynthesis
changes with the age of the cell.
n
Tracer experiments showed that 14C-ferulic acid administered
to gymnosperms is mainly converted to guaiacyl lignin, but
when ferulate is administered to angiosperms it is converted
to guaiacyl-syringyl lignin.
The predominant pathway for monolignol biosynthesis in xylem cells is outlined in black, with the dark arrows showing the primary
substrates and products and the gray arrows showing the minor substrates and products. The blue shading indicates the pathway that is
conserved between angiosperms and gymnosperms, whereas the green shading indicates the angiosperm-specific pathway. The
enzymes and their abbreviations are as follows: CAD, (hydroxy)cinnamyl alcohol dehydrogenase; CCoAOMT, caffeoyl CoA Omethyltransferase; CCR, (hydroxy)cinnamoyl CoA reductase; C3H, p-coumaroyl shikimate/quinate 3-hydroxylase; C4H, cinnamate 4hydroxylase; 4CL, 4-coumarate CoA ligase; COMT, caffeic acid/5-hydroxyferulic acid O-methyltransferase; F5H/Cald5H, ferulate 5hydroxylase/coniferylaldehyde 5-hydroxylase; PAL, phenylalanine ammonia-lyase; SAD, sinapyl alcohol dehydrogenase.
Major Segments of Phenylpropanoid Metabolism in Vascular
Plants as Currently Understood
林木基因體學 vs. 蛋白體學