Ferripyoverdine-reductase activity in Pseudomonas fluorescens.

Enzymatic release of iron from ferripyoverdine through a reductive mechanism was demonstrated in cell-free extracts of Pseudomonas fluorescens. Ferripyoverdine reductase activity was localized primarily in the cytoplasm and/or periplasm and appeared not to be affected by the iron status of the cells. The reaction required a strict anaerobic environment and was fully inhibited by oxygen, whereas NADH was the most effective reductant. Ferripyoverdines from other bacterial sources (P. aeruginosa ATCC 15692, P. fluorescens ATCC 13525, P. fluorescens ATCC 17400) were able to serve as iron sources as well as ferric citrate. However, the activity with ferric citrate was not strongly affected by oxygen and did not display the characteristic lag phase observed with ferripyoverdines, suggesting the occurrence of a specific ferric citrate iron reductase. FMN should play a critical role in the reductive mechanism since it was absolutely required for the activity to occur with an intensively dialyzed cell-free extract, whereas it greatly stimulated (50-fold) the NADH-mediated activity of a crude extract.