Transferases;
Transferring alkyl or aryl groups, other than methyl groups;
Transferring alkyl or aryl groups, other than methyl groups (only sub-subclass identified to date)
The reaction of this bacterial enzyme occurs in three steps, with some of the intermediates presumably remaining enzyme-bound: (a) NAD+-dependent dehydrogenation of either putrescine or spermidine, forming 4-iminobutan-1-amine or (E)-(4-aminobutylidene)(3-aminopropyl)amine, respectively, (b) attack by water forming 4-aminobutanal (and releasing ammonia or propane-1,3-diamine, respectively), and (c) condensation of 4-aminobutanal with putrescine, which forms homospermidine and restores NAD+. Differs from the eukaryotic enzyme EC 2.5.1.45, homospermidine synthase (spermidine-specific), which cannot use putrescine as donor of the aminobutyl group.
Homospermidine synthase of Rhodopseudomonas viridis: Substrate specificity and effects of the heterologously expressed enzyme on polyamine metabolism of Escherichia coli.