The Enzyme Database

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EC 2.5.1.45     
Accepted name: homospermidine synthase (spermidine-specific)
Reaction: spermidine + putrescine = sym-homospermidine + propane-1,3-diamine
For diagram of reaction, click here
Glossary: sym-homospermidine = N1-(4-aminobutyl)butane-1,4-diamine
putrescine = butane-1,4-diamine
spermidine = N1-(3-aminopropyl)butane-1,4-diamine
Systematic name: spermidine:putrescine 4-aminobutyltransferase (propane-1,3-diamine-forming)
Comments: A eukaryotic enzyme found in plants. The reaction occurs in three steps, with some of the intermediates presumably remaining enzyme-bound: (a) NAD+-dependent dehydrogenation of spermidine to 4-iminobutan-1-amine, (b) attack by water forming 4-aminobutanal (and releasing propane-1,3-diamine), and (c) condensation of 4-aminobutanal with purescine, which forms homospermidine and restores NAD+. 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).
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc
References:
1.  Böttcher, F., Ober, D. and Hartmann, T. Biosynthesis of pyrrolizidine alkaloids: putrescine and spermidine are essential substrates of enzymatic homospermidine formation. Can. J. Chem. 72 (1994) 80–85.
2.  Ober, D. and Hartmann, T. Homospermidine synthase, the first pathway-specific enzyme of pyrrolizidine alkaloid biosynthesis, evolved from deoxyhypusine synthase. Proc. Natl. Acad. Sci. USA 96 (1999) 14777–14782. [DOI] [PMID: 10611289]
3.  Ober, D., Harms, R. and Hartmann, T. Cloning and expression of homospermidine synthase from Senecio vulgaris: a revision. Phytochemistry 55 (2000) 311–316. [PMID: 11117877]
[EC 2.5.1.45 created 2001]
 
 


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