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Silver J, al-Jaff G, Taies JA, Wilson MT, den Engelsen D, Fern GR, Ireland TG. Studies on the binding of CO to low-spin [Fe(II)(Por)L 2] complexes: an aid to understanding the binding of CO to haemoglobin and myoglobin. J Biol Inorg Chem 2023; 28:65-84. [PMID: 36478266 PMCID: PMC9938061 DOI: 10.1007/s00775-022-01969-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2022] [Accepted: 10/13/2022] [Indexed: 12/12/2022]
Abstract
The visible and Mössbauer spectra of [Fe(II)(Por)L2] and [Fe(II)(Por)L(CO)] complexes (where Por = protoporphyrin IX (PPIX) or tetra(p-sulfophenyl)porphyrin (TPPS) and L = an aliphatic or aromatic nitrogenous base) are reported and discussed. The results are compared to those of previously reported [Fe(II)(Por)L(CO)] complexes (where Por = PPIX, TPPS, PMXPP, TPP, OMTBP and OEP; L = a nitrogenous aromatic ligand) and HbCO (where Hb = haemoglobin) and MyCO (where My = myoglobin). A new approach, to extracting information from the Mössbauer parameters has been developed by plotting those of the [Fe(II)(Por)L2] complexes against those of [Fe(II)(Por)L(CO)] complexes for the same ligands, has yielded a series of trend lines that show a significant dependence on both the nature of the porphyrin and also of the nitrogenous ligand. Different trend lines were found for aromatic nitrogenous ligands to aliphatic nitrogenous ligands showing that the porphyrins could donate different amounts of charge to the Fe(II) cations as the L ligand changed, and hence, they display electron sink properties. From the plots, it was shown that haemoglobin and myoglobin both bind CO very strongly compared to the model complexes studied herein. Using the reported structural and Mössbauer data for the [Fe(II)(Por)L2] and [Fe(II)(Por)L(CO)] complexes, it proved possible and instructive to plot the Mössbauer parameters against a number of the bond lengths around the Fe(II) cations. The interpretation of the resulting trend lines both supported and facilitated the extension of our findings enabling further understanding of the geometry of the bonding in CO haemoglobin and CO myoglobin.
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Affiliation(s)
- Jack Silver
- grid.7728.a0000 0001 0724 6933College of Engineering, Design and Physical Sciences, School of Engineering, Wolfson Centre for Materials Processing, Brunel University London, Kingston Lane, Uxbridge, UB8 3PH Middlesex UK
| | - Golzar al-Jaff
- grid.8356.80000 0001 0942 6946School of Life Sciences, University of Essex, Wivenhoe Park, Colchester, CO4 3SQ Essex UK ,grid.444950.8Department of Chemistry, College of Education, Salahaddin University-Erbil, Erbil, Iraq
| | - Jehad A. Taies
- grid.8356.80000 0001 0942 6946School of Life Sciences, University of Essex, Wivenhoe Park, Colchester, CO4 3SQ Essex UK ,Department of Chemistry, College of Education for Pure Science, University of Anwar, Ramadi, Iraq
| | - Michael T. Wilson
- grid.8356.80000 0001 0942 6946School of Life Sciences, University of Essex, Wivenhoe Park, Colchester, CO4 3SQ Essex UK
| | - Daniel den Engelsen
- grid.7728.a0000 0001 0724 6933College of Engineering, Design and Physical Sciences, School of Engineering, Wolfson Centre for Materials Processing, Brunel University London, Kingston Lane, Uxbridge, UB8 3PH Middlesex UK
| | - George R. Fern
- grid.7728.a0000 0001 0724 6933College of Engineering, Design and Physical Sciences, School of Engineering, Wolfson Centre for Materials Processing, Brunel University London, Kingston Lane, Uxbridge, UB8 3PH Middlesex UK
| | - Terry G. Ireland
- grid.7728.a0000 0001 0724 6933College of Engineering, Design and Physical Sciences, School of Engineering, Wolfson Centre for Materials Processing, Brunel University London, Kingston Lane, Uxbridge, UB8 3PH Middlesex UK
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Silver J, Al-Jaff G, Wilson MT, den Engelsen D, Fern GR, Ireland TG. Studies on the binding of nitrogenous bases to protoporphyrin IX iron(II) in aqueous solution at high pH values. J Biol Inorg Chem 2022; 27:297-313. [PMID: 35235042 PMCID: PMC8960585 DOI: 10.1007/s00775-022-01929-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2021] [Accepted: 01/14/2022] [Indexed: 10/28/2022]
Abstract
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. 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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Affiliation(s)
- Jack Silver
- College of Engineering, Design and Physical Sciences, School of Engineering, Wolfson Centre for Materials Processing, Brunel University London, Kingston Lane, Uxbridge, UB8 3PH, Middlesex, UK
| | - Golzar Al-Jaff
- School of Life Sciences, University of Essex, Wivenhoe Park, Colchester, CO4 3SQ, Essex, UK.,Department of Chemistry, College of Education, Salahaddin University-Erbil, Erbil, Iraq
| | - Michael T Wilson
- School of Life Sciences, University of Essex, Wivenhoe Park, Colchester, CO4 3SQ, Essex, UK
| | - Daniel den Engelsen
- College of Engineering, Design and Physical Sciences, School of Engineering, Wolfson Centre for Materials Processing, Brunel University London, Kingston Lane, Uxbridge, UB8 3PH, Middlesex, UK
| | - George R Fern
- College of Engineering, Design and Physical Sciences, School of Engineering, Wolfson Centre for Materials Processing, Brunel University London, Kingston Lane, Uxbridge, UB8 3PH, Middlesex, UK
| | - Terry G Ireland
- College of Engineering, Design and Physical Sciences, School of Engineering, Wolfson Centre for Materials Processing, Brunel University London, Kingston Lane, Uxbridge, UB8 3PH, Middlesex, UK.
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Abstract
The pH dependence of the peroxidase activity (guaiacol assay) of the ferric hemeoctapeptide N-acetylmicroperoxidase-8 (N-AcMP8) was studied under conditions where formation of the Compound I analogue of the peroxidase enzymes is rate limiting. The pH profile of the reaction rate is consistent with a mechanism where both H2O2 and HO2- can displace H2O coordinated trans to neutral His but where the hydroxo complex of the hemepeptide (OH- trans to His) is kinetically inert. At pH > 11, where the proximal His ligand of Fe(III) ionizes to form a histidinate, the hydroxo complex (OH- trans to His-) becomes kinetically labile. A comparison of DeltaH(double dagger) and DeltaS(double dagger) values for the reaction of H2O2 and HO2-, obtained from the temperature dependence of the rate constants, with values for CN- and cysteine reported previously, shows that the activation parameters depend on the identity of the incoming ligand. This suggests that ligand substitution at Fe(III) in N-AcMP8 proceeds through an interchange mechanism.
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Affiliation(s)
- Helder M Marques
- Molecular Sciences Institute, School of Chemistry, University of the Witwatersrand, P.O. Wits, Johannesburg, 2050 South Africa.
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Spee JH, Boersma MG, Veeger C, Samyn B, Van Beeumen J, Warmerdam G, Canters GW, Van Dongen WM, Rietjens IM. The influence of the peptide chain on the kinetics and stability of microperoxidases. EUROPEAN JOURNAL OF BIOCHEMISTRY 1996; 241:215-20. [PMID: 8898909 DOI: 10.1111/j.1432-1033.1996.0215t.x] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Microperoxidases with increasing lengths of the peptide attached to the heme moiety have been isolated after proteolytic digestion of horse-heart cytochrome c (microperoxidases 6, 8, and 11) and of cytochrome c550 from Thiobacillus versutus (microperoxidase 17). The different microperoxidases catalyze the H2O2-dependent para-hydroxylation of aniline relatively efficiently but are rapidly inactivated under turnover conditions. The horse-heart cytochrome-c-derived microperoxidases have identical values for Vmax but show a decrease of the K(m) for aniline and a higher stability when the attached peptide is longer. The kinetic constants obtained for microperoxidase 17, differ markedly from the microperoxidases derived from horse-heart cytochrome c. Possible factors underlying the observed differences are discussed.
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Affiliation(s)
- J H Spee
- Department of Biochemistry, Agricultural University, Wageningen, The Netherlands
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Marsh PJ, Silver J, Symons MCR, Taiwo FA. Mössbauer and electron paramagnetic resonance studies on some new bis-(ligated) porphyrinatoiron(III) complexes with aliphatic amines. Models for cytochromes b. ACTA ACUST UNITED AC 1996. [DOI: 10.1039/dt9960002361] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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