EC - Homospermidine synthase (spermidine-specific)

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IntEnz Enzyme Nomenclature


Accepted name:
homospermidine synthase (spermidine-specific)
Systematic name:
spermidine:putrescine 4-aminobutyltransferase (propane-1,3-diamine-forming)




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, 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

Enzymes and pathways: NC-IUBMB , BRENDA , DIAGRAM , ExplorEnz , ENZYME@ExPASy , KEGG , MetaCyc , UniPathway
Structural data: CSA , EC2PDB
Gene Ontology: GO:0050514


  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: 80-85 (1994).
  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: 14777-14782 (1999). [PMID: 10611289]
  3. Ober, D., Harms, R. and Hartmann, T.
    Cloning and expression of homospermidine synthase from Senecio vulgaris: a revision.
    Phytochemistry 55: 311-316 (2000).

[EC created 2001]