The intracellular polyamine contents are regulated not only by polyamine
biosynthesis and transport but also by polyamine degradation catalyzed
by copper-dependent amine oxidase (DAO) and FAD-dependent polyamine
oxidase (PAO). The genome sequence of Synechocystis sp. PCC 6803 reveals
the presence of at least one putative polyamine oxidase gene, slr5093.
The open reading frame of slr5093 encoding Synechocystis polyamine
oxidase (SynPAO, E.C. 1.5.3.17) was expressed in Escherichia coli. The
purified recombinant enzyme had the characteristic absorption spectrum
of a flavoprotein with absorbance peaks at 380 and 450 nm. The optimum
pH and temperature for the oxidation of both spermidine and spermine are
8.5 and 30 °C, respectively. The enzyme catalyzed the conversion of
spermine and spermidine to spermidine and putrescine, respectively, with
higher catalytic efficiency when spermine served as substrate. These
results suggest that SynPAO is a polyamine oxidase involved in a
polyamine back-conversion pathway. Based on the structural analysis,
Gln94, Tyr403 and Thr440 in SynPAO are predicted to be important
residues in the active site.