Iron chelation properties of an extracellular siderophore exochelin MS.

Journal Article (Journal Article)

The coordination chemistry of an extracellular siderophore produced by Mycobacterium smegmatis, exochelin MS (ExoMS), is reported along with its pK(a) values, Fe(III) and Fe(II) chelation constants, and aqueous solution speciation as determined by spectrophotometric and potentiometric titrations. Exochelin MS has three hydroxamic acid groups for Fe(III) chelation and has four additional acidic protons from a carboxylic acid group and three primary amine groups, on the backbone of the molecule. The pK(a) values for the three hydroxamic acid moieties, the carboxylic acid group and the alkylammonium groups on ExoMS, correspond well with the literature values for these moieties. Equilibrium constants for proton-dependent Fe(III)-ExoMS equilibria were determined using a model involving the sequential protonation of the Fe(III)-ExoMS complexes at the first and second coordination shells. The equilibrium constants (beta) for the overall formation of Fe(III)ExoMS(H(3))(2+) and Fe(II)ExoMS(H(3))(+) from Fe((aq))(3+) or Fe((aq))(2+) and the deprotonated hydroxamate coordinating group form of the siderophore, ExoMS(H(3))(-), are calculated as log beta(III) = 28.9 and log beta(II) = 10.1. A calculated pFe value of 25.0 is very similar to that of other linear trihydroxamic acid siderophores, and indicates that ExoMS is thermodynamically capable of removing Fe(III) from transferrin. The E(1/2) for the Fe(III)-ExoMS/Fe(II)-ExoMS couple was determined from quasi reversible cyclic voltammograms at pH = 6.5 and found to be -380 mV.

Full Text

Duke Authors

Cited Authors

  • Dhungana, S; Ratledge, C; Crumbliss, AL

Published Date

  • October 2004

Published In

Volume / Issue

  • 43 / 20

Start / End Page

  • 6274 - 6283

PubMed ID

  • 15446873

Electronic International Standard Serial Number (EISSN)

  • 1520-510X

International Standard Serial Number (ISSN)

  • 0020-1669

Digital Object Identifier (DOI)

  • 10.1021/ic049343e


  • eng