Magnetic circular dichroism spectra of soybean leghaemoglocin a at room temperature and 4.2 K

Sievers, Gunnel; Gadsby, P M A; Peterson, Jim; Thomson, Andrew J.

doi:10.1016/0167-4838(83)90283-2

Cited by 41 publications

(37 citation statements)

References 31 publications

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“…The EPR signals at 2.96, 2.3 and 1.48, the visible-region MCD spectra and the near-IR MCD band at 1510 nm point to the presence of low-spin ferric heme co-ordinated by two histidine residues [6,7]. The spin integrations of the EPR signals in the oxidised and cyanide adducts giving 1.7 spins per molecule of enzyme suggest that two hemes have this co-ordination.…”

Section: Discussionmentioning

confidence: 86%

Electron paramagnetic resonance and magnetic circular dichroism studies of a hexa‐heme nitrite reductase from Wolinella succinogenes

et al. 1987

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The nature of the heme centers in the hexa-heme dissimilatory nitrite reductase from the bacterium Wolinella succinogenes has been investigated with EPR and magnetic circular dichroism spectroscopy. The EPR spectrum of the ferric enzyme is complex showing, in addition to magnetically isolated low-spin ferric hemes with g values of 2.93, 2.3 and 1.48, two sets of signals at g= 10.3, 3.7 and 4.8, 3.21, which we assign to two pairs of exchange coupled hemes. The MCD spectra show that the isolated hemes are bis-histidine coordinated and that there is one high-spin ferric heine. The exchange coupling is lost on treatment with SDS.

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Section: Discussionmentioning

confidence: 86%

Electron paramagnetic resonance and magnetic circular dichroism studies of a hexa‐heme nitrite reductase from Wolinella succinogenes

et al. 1987

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“…These pK a values are about 7 and 6 units lower than that of free imidazole, Scheme 1, and about 3 and 2 units lower than the equivalent pK a values for metMb and metHb [18, 50]. The most acidic of all heme-bound imidazoles is that of soybean legHb, with a reported pK a of between 6.5 and 7.0 [51]. …”

Section: Discussionmentioning

confidence: 99%

Binding of imidazole, 1-methylimidazole and 4-nitroimidazole to yeast cytochrome c peroxidase (CcP) and the distal histidine mutant, CcP(H52L)

Erman

Chinchilla

Studer

et al. 2015

Biochimica et Biophysica Acta (BBA) - Proteins and Proteomics

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Imidazole, 1-methylimidazole and 4-nitroimidazole bind to yeast cytochrome c peroxidase (yCcP) with apparent equilibrium dissociation constants (KDnormalapp) of 3.3 ± 0.4, 0.85 ± 0.11, and ~0.2 M, respectively, at pH 7. This is the weakest imidazole binding to a heme protein reported to date and it is about 120 times weaker than imidazole binding to metmyoglobin. Spectroscopic changes associated with imidazole and 1-methylimidazole binding to yCcP suggest partial ionization of bound imidazole to imidazolate. The pKa for ionization of bound imidazole is estimated to be 7.4 ± 0.2, about 7 units lower than that of free imidazole and about 3 units lower than imidazole bound to metmyoglobin. Equilibrium binding of imidazole to CcP(H52L) is biphasic with low- and high-affinity phases having KDnormalapp values of 9.5 ± 4.5 and 0.13 ± 0.04 M, respectively. CcP(H52L) binding of 1-methylimidazole is monophasic with an affinity similar to those of yCcP and rCcP. Binding of 1-methylimidazole to rCcP is associated with two kinetic phases, the initial binding complete within 10 s, followed by a process that is consistent with 1-methylimidazole binding to a cavity created by movement of Trp-191 from the interior of the protein to the surface. Both the equilibrium binding and kinetics of 1-methylimidazole binding to yCcP are pH dependent. yCcP has a four-fold increase in 1-methylimidazole binding affinity on decreasing the pH from 7.5 to 4.0, an observation that is unique among the many studies on binding of imidazole and imidazole derivatives to heme proteins.

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“…10. Scheme of a plausible coupling of electron and proton transfers in a cytochrome containing two histidylimidazoles as heme ligands; VLP, very low potential; LP, low potential; HP, high potential ferriheme have actually been characterized between pH 6.5 and 9.0 in oxidized leghemoglobin, cyt c' and cyt b562 (Weber 1982;Sievers et al 1983;Moore et al 1985). Therefore, assuming that the difference of 3-4 pKa units between Fe (III) PP (ImH)2 and Fe (II) PP (ImH)z is roughly kept constant between the oxidized and the reduced forms of heme in hemoproteins, the mono-and bis-(histidine) complexes of natural iron-porphyrins are potentially able to transfer one or two proton(s) per electron under favorable environmental conditions.…”

Section: Iron Oxidation and Imidazole Deprotonationmentioning

confidence: 99%

Redox control of proton transfers in membrane b-type cytochromes: an absorption and resonance Raman study on bis(imidazole) and bis(imidazolate) model complexes of iron-protoporphyrin

Desbois

Lutz

1992

Eur Biophys J

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Abstract. Optical absorption spectra and resonance Raman (RR) spectra, obtained with Soret excitation, are reported for bis(imidazole) and bis(imidazolate) complexes of iron(II)-and iron(III)-protoporphyriri IX, prepared in aqueous conditions. Perdeuteration experiments on the axial ligands permitted the assignment of the symmetric Fe-(ligand)2 stretching mode of Fe[x]PP(L)2 to RR bands at 203 (x=II; L=ImH), 212 (x=II; L=Im-), 201 (x=III; L=ImH) and 226 cm -1 (x = III; L = Im-). These frequency differences indicate a strengthening of the axial bonds when the imidazole deprotonations occur. The larger difference observed for the ferric derivatives reflects the stronger a-donor capability of the Ira-anion for iron(III) over iron(II). For the ferrous derivatives, the frequencies of several skeletal porphyrin modes (v4, Vlo, vll and V3s ) are downshifted by 2-10 cm-J upon deprotonation of the ligands. This effect corresponds to an increased back-bonding from the metal atom to the porphyrin ring when the axial ligand decreases its n-acid strength. Bringing further support to this interpretation, an inverse linear relationship is established between the frequencies of v (Fe(II)-L2) and v~t. This correlation is expected to monitor the overall Hbonding state of histidine ligands of reduced cytochromes b. On the other hand, absorption measurements have characterized large pK~ differences for the sequential imidazole ionizations of Fe Abbreviations: RR, resonance Raman; EPR, electron paramagnetic resonance; PP, protoporphyrin IX; ImH, imidazole; Ira-, imidazolate; Im*, imidazole or imidazolate; 1Melm, t-methylimidazole; HisH, histidine; His-, histidinate; CTABr, cetyltrimethylammonium bromide; NaDS, sodium dodecylsulphate; VLP, very low potential; LP, low potential; HP, high potential good proton-acceptor and proton-donor, respectively, and suggest a model by which heme, located in a favorable environment inside a cytochrome, could couple a cycle of electron transfer with a proton transfer. Based on sequence data and structural models, it is further proposed that, in several membrane cytochromes b (b, b6, b559) , a positively charged amino acid residue and an imidazolate ligand of the ferriheme could form an ion pair involved in a redox control of proton transfer.

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Magnetic circular dichroism spectra of soybean leghaemoglocin a at room temperature and 4.2 K

Cited by 41 publications

References 31 publications

Electron paramagnetic resonance and magnetic circular dichroism studies of a hexa‐heme nitrite reductase from Wolinella succinogenes

Electron paramagnetic resonance and magnetic circular dichroism studies of a hexa‐heme nitrite reductase from Wolinella succinogenes

Binding of imidazole, 1-methylimidazole and 4-nitroimidazole to yeast cytochrome c peroxidase (CcP) and the distal histidine mutant, CcP(H52L)

Redox control of proton transfers in membrane b-type cytochromes: an absorption and resonance Raman study on bis(imidazole) and bis(imidazolate) model complexes of iron-protoporphyrin

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