FLUORESCENT PSEUDOMONAD PYOVERDINES BIND AND OXIDIZE FERROUS ION

Major pyoverdines from Pseudomonas fluorescens 2-79 (Pf-B), P. aerugin osa ATCC 15692 (Pa-C), and P, putida ATCC 12633 (Pp-C) were examined b y absorption and fluorescence spectroscopic techniques to investigate the interaction between ferrous ion and the pyoverdine ligand. At phys iological pH ferrous ion quenched the fluorescence of all three pyover dines much faster than ferric ion did, Also, increased absorbance at 4 60 nm was observed to be much faster for Fe2+-pyoverdine than for Fe3-pyoverdine. At pH 7.4, about 90% of Fe3+ was bound by pyoverdine Pa-C after 24 h whereas Fe2+ was bound by the pyoverdine completely in onl y 5 min, The possibility that Fe2+ underwent rapid autoxidation before being bound by pyoverdine was considered unlikely, since the Fe2+ con centration in pyoverdine-free samples remained constant over a 3-min p eriod at pH 7.4, Incubating excess Fe2+ with pyoverdine in the presenc e of 8-hydroxyquinoline, an Fe3+-specific chelating agent, resulted in the formation of a Fe3+-hydroxyquinoline complex, suggesting that the iron in the Fe2+ pyoverdine complex existed in the oxidized form. The se results strongly suggested that pyoverdines bind and oxidize the fe rrous ion.