title: Iron binding to Azotobacter salinestris melanin, iron mobilization and uptake mediated by siderophores.
abstract: Iron-sufficient Azotobacter salinestris cells bound large amounts of 55Fe to cell-associated catechol melanin in an energy-independent manner. Iron was mobilized from the cell surface by citric acid and transported into the cell in a process that was inhibited by azide, carbonyl cyanide m-chlorophenyl-hydrazone (CCCP), KCl or RbCl, the latter two known to inhibit Na(+)-dependent activities in A. salinestris. Iron-limited cells produced a hydroxamate compound (HDX) which promoted 55Fe-uptake into iron-limited cells in a two step process. Initial uptake was inhibited by azide or CCCP, but not by KCl, while subsequent uptake was blocked by all inhibitors. Citric acid also mediated energy-dependent 55Fe-uptake in iron-limited cells, but initial iron-uptake was less sensitive to CCCP than HDX-mediated iron-uptake. The results show that melanin serves as an iron trap, probably to protect the cells from oxidative damage mediated by H2O2 and the Fenton reaction. A model for HDX siderophore-mediated iron-uptake is proposed which requires energy to concentrate iron in the periplasm and H+/Na(+)-dependent events to bring iron into the cell.
authors.affiliation: Department of Microbiology, University of Alberta, Edmonton, Canada.
authors.forename: W J
authors.initials: WJ
authors.lastname: Page
authors.forename: S
authors.initials: S
authors.lastname: Shivprasad
mesh_terms: D001386:Azides / Q000494:pharmacology; D001395:Azotobacter / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism; D002712:Chlorides / Q000494:pharmacology; D006877:Hydroxamic Acids / Q000378:metabolism; D007501:Iron / Q000378:metabolism*; D007504:Iron Radioisotopes; D007700:Kinetics; D008543:Melanins / Q000378:metabolism*; D011189:Potassium Chloride / Q000494:pharmacology; D011485:Protein Binding; D012413:Rubidium / Q000494:pharmacology; D017262:Siderophores / Q000502:physiology*
chemical_list: D001386:Azides; D002712:Chlorides; D006877:Hydroxamic Acids; D007504:Iron Radioisotopes; D008543:Melanins; D017262:Siderophores; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D011189:Potassium Chloride; D007501:Iron; D012413:Rubidium; C032710:rubidium chloride