The Enzyme Database

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Accepted name: homospermidine synthase (spermidine-specific)
Reaction: spermidine + putrescine = sym-homospermidine + propane-1,3-diamine
For diagram of reaction, click here
Glossary: sym-homospermidine = N-(4-aminobutyl)butane-1,4-diamine
putrescine = butane-1,4-diamine
spermidine = N-(3-aminopropyl)butane-1,4-diamine
Systematic name: spermidine:putrescine 4-aminobutyltransferase (propane-1,3-diamine-forming)
Comments: 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, 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
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: 11117878]
[EC created 2001]

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