Hydrolytic polymerization of ferric citrate.  II.  Influence of excess citrate

Spiro, Thomas G.; Bates, George W.; Saltman, Paul

doi:10.1021/ja00998a009

Cited by 141 publications

(107 citation statements)

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“…This was confirmed by the electronic absorption spectrum of ferric staphyloferrin A at pH 7.3 (Fig. 3), which resembles that of ferric dicitrate [FeCit2ls [27]. The theoretically possible involvement of the ornithine carboxylate group in ferric ion complexation is very unlikely, since in this case a less favourable tetradentate ligand system would result.…”

Section: Ferric Ioii Complexationmentioning

confidence: 63%

“…The extension of the bidentate a-hydroxycarboxylate ligand to a tridentate bhydroxy, P-carboxy-substituted carboxylate coordination group, as well as the chelate effect obtained by the D-ornithine bridge, obviously provides an increase of the thermodynamic affinity for Fe(III), which enables staphyloferrin A to serve as a siderophore. In comparison, citrate requires a ligand to iron(II1) ratio of about 20 : 1 for formation of the mononuclear Fe(l1I) dicitrate complex at physiological pH [27].…”

Section: Resultsmentioning

confidence: 99%

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Staphyloferrin A: a structurally new siderophore from staphylococci

Konetschny-Rapp

Jung

Meiwes

et al. 1990

European Journal of Biochemistry

139

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Two ferric ion-binding compounds, designated staphyloferrin A and B, were detected in the culture filtrates of staphylococci grown under iron-deficient conditions. Staphyloferrin A was isolated from cultures of Staphylococcus hyicus DSM 20459. The structural elucidation of this highly hydrophilic, acid-labile compound revealed a novel siderophore, N 2 , N 5 -di-(l-oxo-3-hydroxy-3,4-dicarboxybutyl)-~-ornithine, which consists of one ornithine and two citric acid residues linked by two amide bonds. The two citric acid components of staphyloferrin A provide two tridentate pendant ligands, comprising of a /I-hydroxy, P-carboxy-substituted carboxylic acid derivative, for octahedral metal chelation. The CD spectrum of the staphyloferrin A ferric complex indicates a predominant A configuration about the ferric ion center. The uptake of ferric staphyloferrin A by S. hyicus obeys MichaelisMenten kinetics ( K , = 0.246 pM; v,,, = 82 pmol . mg-. min-I), indicating active transport of this siderophore.The staphyloferrin A transport system is different from that of the ferrioxamines as shown by an antagonism test. Production of staphyloferrin A is strongly iron-dependent and is stimulated by supplementation of the medium with either D-or L-ornithine. ~~-[S-'~C]ornithine was incorporated into staphyloferrin A, demonstrating that ornithine is an intermediate in staphyloferrin A biosynthesis.Iron, the fourth most abundant element of the earths crust, is required by all aerobic microorganisms and plays an important role in membrane-bound electron-transport chains as well as in cytoplasmic redox enzymes. In an aerobic environment iron is present in the Fe(II1) oxidized form, which polymerizes into insoluble ferric oxyhydroxides under physiological conditions [l, 21. In mammals, iron is bound to proteins such as lactoferrin and transferrin, and is therefore inaccessible, by direct means, to microorganisms [3]. Thus, microorganisms have developed different strategies to provide themselves with iron. The most common and well-investigated strategy is the high-affinity Fe( 111) uptake via siderophores. During iron deficiency, microorganisms excrete low-molecular-mass iron(II1)-chelating compounds (siderophores) in their iron-free form. After ferric ion chelation, the complexes are actively taken up by specific transport systems [4]. Several hundred siderophores from prokaryotes and eukaryotes are now known, which can structurally be assigned to the major classes of hydroxamate-and catecholate-type siderophores.

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Section: Ferric Ioii Complexationmentioning

confidence: 63%

Section: Resultsmentioning

confidence: 99%

Staphyloferrin A: a structurally new siderophore from staphylococci

Konetschny-Rapp

Jung

Meiwes

et al. 1990

European Journal of Biochemistry

139

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“…To avoid citrate-Fe(III) complex polymerization, all experiments with citrate were performed at c 2 # 10 mm [26]. q FEBS 1999 nonprotonated species at pH values where the free ligand is still in the protonated form [27,28].…”

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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“…This may be attributed to the tendency of many transition metal chelate compounds to polymerize by olation reactions, so that molecular size of the chelate complex will depend upon many factors including pH, metal concentration, denticity of the ligand, and ligand-to-metal ratio. The polymerization reactions have been examined in some detail in the case of iron(m) (Spiro, Bates, and Saltman 1967;Spiro, Pape, and Saltman 1967).…”

Section: Discussionmentioning

confidence: 99%

Effects of Human Alimentary Secretions on 64cu Diffusion in an in Vitro System

Jl¹,

Davis²,

Dj³

1971

Aust. Jnl. Of Bio. Sci.

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Human alimentary secretions are known to form soluble complexes with copper. The passive diffusion rate of 64Cu complexed to human saliva, gastric juice, and bile was determined and compared with that of known synthetic complexing agents. The study was performed using a two-piece glass diffusion apparatus which permitted continuous sampling from each compartment. It was shown that whereas copper diffusion was unimpaired by saliva or gastric juice, it was markedly inhibited by bile. The most likely explanation for this phenomenon is either that copper is bound by a macromolecular component of bile or that a low molecular weight complex is formed with some biliary component and undergoes polymerization. Which of these is applicable has not yet been determined. The possible role of such a mechanism in the regulation of gastrointestinal copper absorption is discussed.

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Hydrolytic polymerization of ferric citrate. II. Influence of excess citrate

Cited by 141 publications

References 0 publications

Staphyloferrin A: a structurally new siderophore from staphylococci

Staphyloferrin A: a structurally new siderophore from staphylococci

Transferrins, the mechanism of iron release by ovotransferrin

Effects of Human Alimentary Secretions on 64cu Diffusion in an in Vitro System

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