Information on EC 2.5.1.45 - homospermidine synthase (spermidine-specific)

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The enzyme appears in viruses and cellular organisms

EC NUMBER
COMMENTARY hide
2.5.1.45
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RECOMMENDED NAME
GeneOntology No.
homospermidine synthase (spermidine-specific)
REACTION
REACTION DIAGRAM
COMMENTARY hide
ORGANISM
UNIPROT
LITERATURE
spermidine + putrescine = sym-homospermidine + propane-1,3-diamine
show the reaction diagram
the reaction of this enzyme occurs in three steps: i. NAD-dependent dehydrogenation of spermidine, ii. transfer of the 4-aminobutylidene group from dehydrospermidine to putrescine, iii. reduction of the imine intermediate to form homospermidine. Hence the overall reaction is transfer of a 4-aminobutyl group. This enzyme is more specific than EC 2.5.1.44, homospermidine synthase, which is found in bacteria, as it cannot use putrescine as donor of the 4-aminobutyl group. Forms part of the biosynthetic pathway of the poisonous pyrrolizidine alkaloids of the ragworts, Senecio
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REACTION TYPE
ORGANISM
UNIPROT
COMMENTARY hide
LITERATURE
aminobutyl group transfer
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PATHWAY
BRENDA Link
KEGG Link
MetaCyc Link
homospermidine biosynthesis
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SYSTEMATIC NAME
IUBMB Comments
spermidine:putrescine 4-aminobutyltransferase (propane-1,3-diamine-forming)
The reaction of this enzyme occurs in three steps, with some of the intermediates presumably remaining enzyme-bound: (a) NAD+-dependent dehydrogenation of spermidine, (b) transfer of the 4-aminobutylidene group from dehydrospermidine to putrescine and (c) reduction of the imine intermediate to form homospermidine. This enzyme is more specific than EC 2.5.1.44, homospermidine synthase, which is found in bacteria, as it cannot use putrescine as donor of the 4-aminobutyl group. Forms part of the biosynthetic pathway of the poisonous pyrrolizidine alkaloids of the ragworts (Senecio).
CAS REGISTRY NUMBER
COMMENTARY hide
259168-77-9
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76106-84-8
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ORGANISM
COMMENTARY hide
LITERATURE
UNIPROT
SEQUENCE DB
SOURCE
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Manually annotated by BRENDA team
Eupatorium pauciflorum
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Manually annotated by BRENDA team
GENERAL INFORMATION
ORGANISM
UNIPROT
COMMENTARY hide
LITERATURE
malfunction
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transgenic tobacco plants are generated expressing Senecio vernalis homospermidine synthase. Analyses of the polyamine content reveals that, in the transgenic plants, about 80% of spermidine is replaced by homospermidine without any conspicuous modifications of the phenotype. Tracer-feeding experiments and gas chromatographic analyses suggest that these high levels of homospermidine are not sufficient to explain the formation of alkaloid precursors
SUBSTRATE
PRODUCT                       
REACTION DIAGRAM
ORGANISM
UNIPROT
COMMENTARY
(Substrate) hide
LITERATURE
(Substrate)
COMMENTARY
(Product) hide
LITERATURE
(Product)
Reversibility
r=reversible
ir=irreversible
?=not specified
putrescine + spermidine
N-(4-aminobutyl)butane-1,4-diamine + propane-1,3-diamine
show the reaction diagram
putrescine + spermine
sym-homospermine + propane-1,3-diamine
show the reaction diagram
spermidine + putrescine
sym-homospermidine + propane-1,3-diamine
show the reaction diagram
NATURAL SUBSTRATES
NATURAL PRODUCTS
REACTION DIAGRAM
ORGANISM
UNIPROT
COMMENTARY
(Substrate) hide
LITERATURE
(Substrate)
COMMENTARY
(Product) hide
LITERATURE
(Product)
REVERSIBILITY
r=reversible
ir=irreversible
?=not specified
putrescine + spermine
sym-homospermine + propane-1,3-diamine
show the reaction diagram
spermidine + putrescine
sym-homospermidine + propane-1,3-diamine
show the reaction diagram
COFACTOR
ORGANISM
UNIPROT
COMMENTARY hide
LITERATURE
IMAGE
INHIBITORS
ORGANISM
UNIPROT
COMMENTARY hide
LITERATURE
IMAGE
1,3-Diaminopropane
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competitive
cadaverine
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mixed type inhibition
Homospermidine
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competitive
spermidine
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competitive
spermine
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mixed type inhibition
KM VALUE [mM]
SUBSTRATE
ORGANISM
UNIPROT
COMMENTARY hide
LITERATURE
IMAGE
0.003
NAD+
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NAD+ functions as an enzyme-bound redoxsystem that is reduced in the first and reoxidized in the second part of the overall reaction. It functions as a coenzyme and not a cosubstrate
0.0135 - 0.015
putrescine
0.012
spermidine
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at 0.1 mM putrescine
additional information
additional information
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TURNOVER NUMBER [1/s]
SUBSTRATE
ORGANISM
UNIPROT
COMMENTARY hide
LITERATURE
IMAGE
0.0032
putrescine
Senecio vernalis
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+ spermidine
Ki VALUE [mM]
INHIBITOR
ORGANISM
UNIPROT
COMMENTARY hide
LITERATURE
IMAGE
0.0063
1,3-Diaminopropane
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0.058
cadaverine
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0.95
Homospermidine
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0.094
spermidine
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0.0022
spermine
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SPECIFIC ACTIVITY [µmol/min/mg]
ORGANISM
UNIPROT
COMMENTARY hide
LITERATURE
pH OPTIMUM
ORGANISM
UNIPROT
COMMENTARY hide
LITERATURE
pH RANGE
ORGANISM
UNIPROT
COMMENTARY hide
LITERATURE
8.7 - 9.9
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about 55% of maximal activity at pH 8.7 and at pH 9.9
SOURCE TISSUE
ORGANISM
UNIPROT
COMMENTARY hide
LITERATURE
SOURCE
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young flower buds, but not mature flowers, express homospermidine synthase and are able to catalyze pyrrolizidine alkaloid biosynthesis
Manually annotated by BRENDA team
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HSS expression stops just before the flower buds open
Manually annotated by BRENDA team
additional information
LOCALIZATION
ORGANISM
UNIPROT
COMMENTARY hide
GeneOntology No.
LITERATURE
SOURCE
MOLECULAR WEIGHT
ORGANISM
UNIPROT
COMMENTARY hide
LITERATURE
174000
gel filtration
SUBUNITS
ORGANISM
UNIPROT
COMMENTARY hide
LITERATURE
?
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x * 41000, SDS-PAGE
tetramer
GENERAL STABILITY
ORGANISM
UNIPROT
LITERATURE
increased instability with higher purification grade
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STORAGE STABILITY
ORGANISM
UNIPROT
LITERATURE
4°C, crude extract, 0.5-1 mM spermidine, 0.5-1 mM NAD+, 1 week, 30% loss of activity
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Purification/COMMENTARY
ORGANISM
UNIPROT
LITERATURE
using Ni-NTA chromatography
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Cloned/COMMENTARY
ORGANISM
UNIPROT
LITERATURE
expressed as a C-terminal his-tagged fusion protein
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expressed in Escherichia coli
expression in Escherichia coli
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gene HSS, semiquantitative RT-PCR expression analysis in tissues