title: Iron(III) coordination chemistry of alterobactin A: a siderophore from the marine bacterium Alteromonas luteoviolacea.
abstract: Alterobactin A is a siderophore produced by the oceanic bacterium Alteromonas luteoviolacea. The thermodynamic stability constant of the ferric alterobactin A (Alt-A) complex was estimated from electrochemical measurements on the basis of a previously reported linear relationship between the reduction potentials and the pH-independent stability constants for known iron(III) complexes. The reduction potential of the ferric alterobactin A complex determined by square wave voltammetry is -0.972 V vs SCE and reversible, corresponding to a thermodynamic stability constant of 10(51+/-2). Potentiometric titration of Fe(III)-Alt-A shows the release of six protons on complexation of Fe(III) to Alt-A. The 1H NMR resonances of the Ga(III)-Alt-A complex show that the C-4, C-5, and C-6 catecholate protons and the C(alpha) and C(beta) protons of both beta-hydroxyaspartate moieties are shifted downfield relative to the free ligand, which along with the potentiometric titration data is consistent with a complex in which Fe(III) is coordinated by both catecholate oxygen atoms and both oxygen atoms of each beta-hydroxyaspartate. The UV-vis spectrum of Fe(III)-Alt-A is invariant over the pH range 4-9, indicating the coordination does not change over a wide pH range. In addition, in the absence of a coordinated metal ion, the serine ester of Alt-A hydrolyzes forming Alt-B.
authors.affiliation: Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106-9510, USA.
authors.forename: Pamela D
authors.initials: PD
authors.lastname: Holt
authors.forename: Richard R
authors.initials: RR
authors.lastname: Reid
authors.forename: Brent L
authors.initials: BL
authors.lastname: Lewis
authors.forename: George W
authors.initials: GW
authors.lastname: Luther
authors.forename: Alison
authors.initials: A
authors.lastname: Butler
mesh_terms: D020591:Alteromonas / Q000737:chemistry; D004355:Drug Stability; D005290:Ferric Compounds / Q000737:chemistry*; D007700:Kinetics; D008958:Models, Molecular; D015394:Molecular Structure; D010456:Peptides, Cyclic / Q000737:chemistry* / Q000302:isolation & purification; D017262:Siderophores / Q000737:chemistry
chemical_list: D005290:Ferric Compounds; D010456:Peptides, Cyclic; D017262:Siderophores; C084558:alterobactin A