Studies on the binding of nitrogenous bases to protoporphyrin IX iron(II) in aqueous solution at high pH values. Part I. Pyridine and imidazole ligands

Al-Jaff, Golzar; Silver, Jack; Wilson, Michael T.

doi:10.1016/s0020-1693(00)84861-6

Cited by 23 publications

(55 citation statements)

References 40 publications

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“…Further evidence for the presence of iron porphyrin in the µoxo dimeric form (and not as the reduced monomeric species) came from the observation that no colour reaction occurred upon the addition of pyridine to freshly isolated liquid-cultured cells or blood-agar-grown cells taken directly from the anaerobic cabinet or to the extracted black pigment. However, a strong red coloration was immediately obtained when a few crystals of either sodium dithionite or dithiothreitol were added ; an observation explained by the fact that protoporphyrin IX-iron(II) bispyridine forms only via biaxial ligation of pyridine with the iron in the II state [21]. Moreover, as the [Fe(III)PPIX] # O structure does not dissociate easily in pyridine, using this as an extractant [2] will only be effective if the dimer is first reduced with dithionite.…”

Section: Resultsmentioning

confidence: 99%

The periodontopathogen Porphyromonas gingivalis binds iron protoporphyrin IX in the μ-oxo dimeric form: an oxidative buffer and possible pathogenic mechanism

Smalley

Silver

Marsh

et al. 1998

Biochemical Journal

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Mössbauer spectroscopy was used to re-evaluate iron protoporphyrin IX, FePPIX, binding and the chemical nature of the black iron porphyrin pigment of Porphyromonas gingivalis. We demonstrate that FePPIX is bound to the cell in the mu-oxo dimeric form, [Fe(III)PPIX]2O, and that the iron porphyrin pigment is also composed of this material. P. gingivalis also assimilated monomeric Fe(II)- and Fe(III)PPIX into mu-oxo dimers in vitro. Scatchard analysis revealed a greater binding maximum of cells for mu-oxo dimers than for monomeric Fe(III)-or Fe(II)PPIX, although the relative affinity constant for the dimers was lower. Formation of [Fe(III)PPIX]2O via reactions of Fe(II)PPIX with oxygen, and its toxic derivatives, would serve as an oxidative buffer and permit P. gingivalis and other black-pigmenting anaerobes to engender and maintain a local anaerobic environment. Tying up of free oxygen species with iron protoporphyrin IX would also reduce and limit Fe(II)PPIX-mediated oxygen-radical cell damage. More importantly, formation of a cell-surface mu-oxo dimer layer may function as a protective barrier against assault by reactive oxidants generated by neutrophils. Selective interference with these mechanisms would offer the possibility of attenuating the pathogenicity of P. gingivalis and other iron protoporphyrin IX-binding pathogens whose virulence is regulated by this reactive molecule.

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Section: Resultsmentioning

confidence: 99%

The periodontopathogen Porphyromonas gingivalis binds iron protoporphyrin IX in the μ-oxo dimeric form: an oxidative buffer and possible pathogenic mechanism

Smalley

Silver

Marsh

et al. 1998

Biochemical Journal

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124

180

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“…The linear dependence (r 2 = 0.98) of the midpoint reduction potential of the complex between a pyridine ligand, L, and the acid dissociation constant of L, pK L . [74]; others have found that the equilibrium constants for the binding of a series of pyridines and imidazole by ferrous PPIX [49], and of pyridines by isoelectronic Co III OEP [78], increase with the pK L of the ligand, an observation rationalized [49] by suggesting that Fe II and H + behave in similar manner towards L.…”

Section: Factors Affecting the Stability Of Complexes Between Pyridinmentioning

confidence: 97%

“…The bis-imidazole [46] and bis-histidine [43] complexes of Fe II PPIX are monomeric and low spin in 50% ethanol-water solutions. Mö ssbauer studies on the binding of nitrogen donor ligands such as aliphatic amines [47], pyridines and substituted pyridines [48,49], by ferroPPIX and ferrodeuteroporphyrin show that the species formed are six-coordinate low spin complexes.…”

Section: Introductionmentioning

confidence: 99%

The coordination of imidazole and substituted pyridines by the hemeoctapeptide N-acetyl-ferromicroperoxidase-8 (FeIINAcMP8)

Vashi

Marques

2004

Journal of Inorganic Biochemistry

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“…We have previously reported studies on a wide range of nitrogenous ligands binding to [Fe(II)(PPIX)] [ 43 , 44 ]. These studies covered the binding of [Fe(II)(PPIX)] to pyridine, substituted pyridines, imidazoles, aliphatic amines and piperidine.…”

Section: Introductionmentioning

confidence: 99%

“…In our approach we used plots of pKa—log β 2 and of Δ E Q (Mössbauer parameter)—log β 2 to analyse the results. This then innovative combination/display of the data was used to underpin our conclusions [ 43 , 44 ]. It will be used here in a more complete way to take our previous results with those reported herein to allow an overview of the bonding properties of the axial ligands to [Fe(II)(PPIX)] and how they affect the properties of both the iron atom and the PPIX ligand.…”

Section: Introductionmentioning

confidence: 99%

Studies on the binding of nitrogenous bases to protoporphyrin IX iron(II) in aqueous solution at high pH values

et al. 2022

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Studies are reported on the formation of low-spin six-coordinate [Fe(PPIX)L2] complexes from iron(II) protoporphyrin where L is one of a series of nitrogenous ligands (aliphatic, aromatic or heterocyclic). The bonding constants have been determined by titration of the metal complex with these ligands and are compared in relation to previous studies. The adduct formation was monitored utilising optical spectroscopy. In addition, Mӧssbauer spectroscopic experiments were conducted to monitor the electronic environment around the central iron atom in these complexes. The two complementary spectroscopic methods indicated that all nitrogen ligands formed low-spin octahedral complexes. The magnitude of the overall binding constants (β2 values) are discussed and related to (a) the pKa values of the free ligands and (b) the Mössbauer parameter ΔEQ, which represents the quadrupole splitting of the haem iron. The β2 and ΔEQ values are also discussed in terms of the structure of the ligand. Cooperative binding was observed for nearly all the ligands with Hill coefficients close to 2 for iron(II) protoporphyrin; one of these ligands displayed a much greater affinity than any we previously studied, and this was a direct consequence of the structure of the ligand. Overall conclusions on these and previous studies are drawn in terms of aliphatic ligands versus aromatic ring structures and the absence or presence of sterically hindered nitrogen atoms. The implications of the work for the greater understanding of haem proteins in general and in particular how the nitrogenous ligand binding results are relevant to and aid the understanding of the binding of inhibitor molecules to the cytochrome P450 mono-oxygenases (for therapeutic purposes) are also discussed. Graphical abstract Changes in the electronic absorption spectra of five-coordinate [Fe(II)(PPIX)(2-MeIm)] that occurred as the temperature was lowered from room temperature to 78° K

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Studies on the binding of nitrogenous bases to protoporphyrin IX iron(II) in aqueous solution at high pH values. Part I. Pyridine and imidazole ligands

Cited by 23 publications

References 40 publications

The periodontopathogen Porphyromonas gingivalis binds iron protoporphyrin IX in the μ-oxo dimeric form: an oxidative buffer and possible pathogenic mechanism

The periodontopathogen Porphyromonas gingivalis binds iron protoporphyrin IX in the μ-oxo dimeric form: an oxidative buffer and possible pathogenic mechanism

The coordination of imidazole and substituted pyridines by the hemeoctapeptide N-acetyl-ferromicroperoxidase-8 (FeIINAcMP8)

Studies on the binding of nitrogenous bases to protoporphyrin IX iron(II) in aqueous solution at high pH values

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