IUBMB Enzyme Nomenclature


Accepted name: homospermidine synthase (spermidine-specific)

Reaction: spermidine + putrescine = sym-homospermidine + propane-1,3-diamine

For reaction pathway click here.

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, CAS registry number:


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. [PMID: 16526057]

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. [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.

[EC created 2001]

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