Composition and Stability of Iron and Copper Citrate Complexes in Aqueous Solution

Field, Terrence B.; McCourt, Janet L.; McBryde, W. A. E.

doi:10.1139/v74-458

Cited by 135 publications

(65 citation statements)

References 6 publications

(5 reference statements)

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“…Under these conditions, citrate had to in a large increase in the amounts of these proteins (Fig. 5 (30), which presumably exceed that of iron citrate by several orders of magnitude (numbers at pH 7 are for various reasons not available [22,37]). The iron citrate complex has just the right properties in that it is strong enough that an outer membrane transport system has evolved for transport of the complex and sufficiently weak that it donates iron to the Sfu system.…”

Section: Resultsmentioning

confidence: 99%

Iron transport systems of Serratia marcescens

1992

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Serratia marcescens W225 expresses an unconventional iron(III) transport system. Uptake of Fe3+ occurs in the absence of an iron(III)-solubilizing siderophore, of an outer membrane receptor protein, and of the TonB and ExbBD proteins involved in outer membrane transport. The three SfuABC proteins found to catalyze iron(III) transport exhibit the typical features of periplasmic binding-protein-dependent systems for transport across the cytoplasmic membrane. In support of these conclusions, the periplasmic SfuA protein bound iron chloride and iron citrate but not ferrichrome, as shown by protection experiments against degradation by added V8 protease. The cloned sfuABC genes conferred upon an Escherichia coli aroB mutant unable to synthesize its own enterochelin siderophore the ability to grow under iron-limiting conditions (in the presence of 0.2 mM 2.2'-dipyridyl). Under extreme iron deficiency (0.4 mM 2.2'-dipyridyl), however, the entry rate of iron across the outer membrane was no longer sufficient for growth. Citrate had to be added in order for iron(III) to be translocated as an iron citrate complex in a FecA-and TonB-dependent manner through the outer membrane and via SfuABC across the cytoplasmic membrane. FecA-and TonB-dependent iron transport across the outer membrane could be clearly correlated with a very low concentration of iron in the medium. Expression of the sfuABC genes in E. coli was controlled by the Fur iron repressor gene. S. marcescens W225 was able to synthesize enterochelin and take up iron(III) enterochelin. It contained an iron(III) aerobactin transport system but lacked aerobactin synthesis. This strain was able to utilize the hydroxamate siderophores ferrichrome, coprogen, ferrioxamine B, rhodotorulic acid, and schizokinen as sole iron sources and grew on iron citrate as well. In contrast to E. coli K-12, S. marcescens could utilize heme. DNA fragments of the E. coli fhuA, iut, exbB, and fur genes hybridized with chromosomal S. marcescens DNA fragments, whereas no hybridization was obtained between S. marcescens chromosomal DNA and E. colifecA,JhuE, and tonB gene fragments. The presence of multiple iron transport systems was also indicated by the increased synthesis of at least five outer membrane proteins (in the molecular weight range of 72,000 to 87,000) after growth in low-iron media. Serratia liquefaciens and Serratia ficaria produced aerobactin, showing that this siderophore also occurs in the genus Serratia.

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Section: Resultsmentioning

confidence: 99%

Iron transport systems of Serratia marcescens

1992

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“…Citrate is capable of binding both Fe(II) and Fe(III) in mononuclear complexes (42). Citrate binds Fe(II) with much lower affinity, however (43), and it is presently unclear how cytosolic Fe(II) can be exported by the IceT transporter. Perhaps chelation by citrate promotes the oxidation of Fe(II) to Fe(III), as has been demonstrated for desferrioxamine (23).…”

Section: Discussionmentioning

confidence: 99%

Iron and citrate export by a major facilitator superfamily pump regulates metabolism and stress resistance inSalmonellaTyphimurium

Frawley¹,

Crouch²,

Bingham-Ramos³

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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The efficacy of antibiotics and host defenses has been linked to the metabolic and redox states of bacteria. In this study we report that a stress-induced export pump belonging to the major facilitator superfamily effluxes citrate and iron from the enteric pathogen Salmonella Typhimurium to arrest growth and ameliorate the effects of antibiotics, hydrogen peroxide, and nitric oxide. The transporter, formerly known as MdtD, is now designated IceT (iron citrate efflux transporter). Iron efflux via an iron-chelating tricarboxylic acid cycle intermediate provides a direct link between aerobic metabolism and bacterial stress responses, representing a unique mechanism of resistance to host defenses and antimicrobial agents of diverse classes.

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“…With ovotransferrin, after the fast proton assisted decarbonation (Eqn 9), the first step in iron release from the C-lobe is a slow proton transfer (Eqn 16), followed by two possible paths, each of which depends on the strength of the competing ligand (Eqns 17±19 and 23). In the presence of a strong iron chelator such as citrate [22] …”

Section: Discussionmentioning

confidence: 99%

Transferrins, the mechanism of iron release by ovotransferrin

Abdallah

Chahine

1999

European Journal of Biochemistry

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Iron release from ovotransferrin in acidic media (3 , pH , 6) occurs in at least six kinetic steps. The first is a very fast (# 5 ms) decarbonation of the iron-loaded protein. Iron release from both sites of the protein is controlled by what appear to be slow proton transfers. The N-site loses its iron first in two steps, the first occurring in the tenth of a second range with second order rate constant k 1 = (2.30^0.10) Â 10 4 m 21´s21 , first order rate constant k 21 = (1.40^0.10) s 21 and equilibrium constant K 1a = (60^6) mm. The second step occurs in the second range with a second order rate constant k 2 = (5.2^0.15) Â 10 3 m 21´s21 , first order rate constant k 22 = (0.2^0.02) s 21 and equilibrium constant K 2a = (39^5) mm. Iron is afterward lost from the C-site of the protein by two different pathways, one in the presence of a strong Fe(III) ligand such as citrate and the other in the presence of weak ligands such as formate or acetate. The first step, common to both paths, is a slow proton uptake which occurs in the tens of second range with a second order rate constant k 3 = (1.22^0.03) Â 10 3 m 21´s21 and equilibrium constant K 3a = (1.0^0.1) mm. In the presence of citrate, this step is followed by formation of an intermediate complex with monoferric ovotransferrin; stability constant K LC = (0.435^0.015) mm. This last step is rate-controlled by slow proton gain which occurs in the hundred second range with a second order rate constant k 4 = (1.05^0.05) Â 10 4 m 21´s21 , first order rate constant k 24 = (1.0^0.1) Â 10 22 s 21 and equilibrium constant K 4a = (0.95^0.15) mm. In the presence of a weak iron(III) ligand such as acetate or formate, formation of an intermediate complex is not detected and iron release is controlled by two final slow proton uptakes. The first occurs in the hundred to thousand second range, second order rate constant k 5 = (6.90^0.30) Â 10 6 m 21´s21 . The last step occurs in the thousand second range. Iron release by ovotransferrin is similar but not identical to that of serum-transferrin. It is slower and occurs at lower pH values. However, as seen for serum-transferrin, it seems to involve the protonation of the amino acid sidechains involved in iron co-ordination and perhaps those implicated in interdomain H-bonds. The observed proton transfers are, then, probably controlled by the change in conformation of the binding lobes from closed when iron-loaded to open in the apo-form.Keywords: transferrin; ovotransferrin; iron metabolism; stopped-flow.Transferrins constitute the most important iron regulation system in vertebrates and some invertebrates, such as worms and insects [1]. Soluble transferrins, such as serum-transferrin, lactoferrin and ovotransferrin, are glycoproteins consisting of a single chain of about 700 amino acids and 80 kDa. These proteins have very similar 3D structures and are all bilobal. Each lobe contains an iron complexation cleft, in which the metal is co-ordinated to the side-chains of four amino acid ligands and a synergistic carbonate or bicarbonate...

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Composition and Stability of Iron and Copper Citrate Complexes in Aqueous Solution

Cited by 135 publications

References 6 publications

Iron transport systems of Serratia marcescens

Iron transport systems of Serratia marcescens

Iron and citrate export by a major facilitator superfamily pump regulates metabolism and stress resistance inSalmonellaTyphimurium

Transferrins, the mechanism of iron release by ovotransferrin

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