Reaction: (1) 2 putrescine = sym-homospermidine + NH3 + H+
(2) putrescine + spermidine = sym-homospermidine + propane-1,3-diamine
For reaction pathway click here.
dehydroputrescine = 4-iminobutan-1-amine
sym-homospermidine = N-(4-aminobutyl)butane-1,4-diamine
putrescine = butane-1,4-diamine
Systematic name: putrescine:putrescine 4-aminobutyltransferase (ammonia-forming)
Comments: The reaction of this enzyme occurs in three steps, with some of the intermediates presumably remaining enzyme-bound: NAD+-dependent dehydrogenation of putrescine (1a), transfer of the 4-aminobutylidene group from dehydroputrescine to a second molecule of putrescine (1b) and reduction of the imine intermediate to form homospermidine (1c). Hence the overall reaction is transfer of a 4-aminobutyl group. Differs from EC 188.8.131.52, homospermidine synthase (spermidine-specific), which cannot use putrescine as donor of the aminobutyl group.
Links to other databases: BRENDA, EXPASY, KEGG, Metacyc, PDB, CAS registry number: 76106-84-8
1. Tait, G.H. The formation of homospermidine by an enzyme from Rhodopseudomonas viridis. Biochem. Soc. Trans. 7 (1979) 199-200. [PMID: 437275]
2. 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]
3. Yamamoto, S., Nagata, S. and Kusaba, K. Purification and characterization of homospermidine synthase in Acinetobacter tartarogens ATCC 31105. J. Biochem. 114 (1993) 45-49. [PMID: 8407874]
4. Srivenugopal, K.S. and Adiga, P.R. Enzymatic synthesis of sym-homospermidine in Lathyrus sativus T (grass pea) seedlings. Biochem. J. 190 (1980) 461-464. [PMID: 7470060]
5. Ober, D., Tholl, D., Martin, W. and Hartmann, T. Homospermidine synthase of Rhodopseudomonas viridis: Substrate specificity and effects of the heterologously expressed enzyme on polyamine metabolism of Escherichia coli. J. Gen. Appl. Microbiol. 42 (1996) 411-419.
6. 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]