Heme rotational isomerism is not required for the production of Q-band splitting in the spectra of iron-porphyrin proteins

Difeo, Thomas J.; Addison, Anthony W.

doi:10.1021/ic00005a052

Cited by 4 publications

(2 citation statements)

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“…A similar split in the absorption spectrum of metal-myoglobin was attributed to a 180°flip of the heme (Cowan & Gray, 1989a), which is known to occur (La Mar et al, 1984). This possibility is eliminated in cyt c because the heme periphery is tethered in two places to the polypeptide chain and has also been discounted in ligated forms of myoglobin (DiFeo & Addison, 1991).…”

Section: Discussionmentioning

confidence: 99%

Spectral Splitting in the α (Q_0,0) Absorption Band of Ferrous Cytochrome c and Other Heme Proteins

et al. 1996

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The alpha or Q0,0 absorption band of horse iron(II) cytochrome c splits and shifts to the blue as temperature decreases over the temperature range of 290-10 K. At room temperature, its maximum is at 18 150 cm-1 and the spectral width is 273 cm-1, whereas at 10 K, the two bands of the Q0,0 transition occur at 18 364 and 18 253 cm-1 and the width of the lowest-energy band is 96 cm-1. Temperature dependent splitting also occurs for zinc cytochrome c, a derivative in which Fe has been replaced by Zn; at 10 K, the peaks in the Q0,0 band region occur at 17 106 and 16 996 cm-1. The peak positions are independent of the cryosolvent (aqueous ethylene glycol or glycerol mixtures). The splitting of the Q0,0 band seen in the protein (approximately 110 cm-1 for iron and zinc cytochrome c) is comparable to the crystal field splitting observed for metalloporphyrins in mixed crystals. In contrast, the Q0,0 band of zinc coproporphyrin III in a glassy solvent (dimethylformamide/ethylene glycol) or in poly(vinyl chloride) shows a blue shift with temperature decrease but no evidence of Q0,0 splitting. Available spectral data show that the Q0,0 band is composed of two nearly degenerate electronic transitions and the split is due to the asymmetry in the heme pocket of the protein that arises from the surrounding polypeptide chain. This asymmetry results in the stabilization of one form of the excited state over the other, according to a Jahn-Teller mechanism.

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Section: Discussionmentioning

confidence: 99%

Spectral Splitting in the α (Q_0,0) Absorption Band of Ferrous Cytochrome c and Other Heme Proteins

et al. 1996

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“…The coupled redox centre in such enzymes displays a remarkable diversity of optical features and redox chemistry, and so no single enzyme can be used as a satisfactory paradigm for understanding the electronic character of the rather unique redox centre in this class. The influence of protein side chains on haem spectra is well documented in the literature of haem proteins (Smith and Williams, 1970;Cowan and Gray, 1989;DiFeo and Addison, 1991), and it is likely that the observed differences in spectral behaviour and redox potentials are induced by variations in the protein environment surrounding each coupled centre. The implications of this observation for the comparison of functional activity have yet to be resolved.…”

Section: Introductionmentioning

confidence: 88%

Electronic properties of the dissimilatory sulphite reductase from Desulfovibrio vulgaris (Hildenborough): comparative studies of optical spectra and relative reduction potentials for the [Fe4S4]-sirohaem prosthetic centres

Lui

Soriano

Cowan

1994

Biochemical Journal

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The dissimilatory sulphite reductase (desulfoviridin) from the sulphate-reducing bacterium Desulfovibrio vulgaris (Hildenborough) displays distinct optical and redox characteristics relative to the haem subunit of Escherichia coli assimilatory sulphite reductase. For high-spin pentaco-ordinate desulfoviridin there is minimal change in the absorbance of the oxidized chromophores both after reduction or after addition of exogenous ligands. A ligand-metal charge-transfer band approximately 702 nm is observed in both the oxidized and one-electron-reduced enzyme. E.p.r. spectroscopy has been used to define the relative reduction potentials for sirohaem and [Fe4S4] centres (delta E0 = Es0-Ec0) as a function of sirohaem axial co-ordination. Typically delta E0 lies in a range from -10 to -50 mV. These results show a correlation with the sigma-donor or pi-acceptor properties of the ligand and stand in sharp contrast with estimates for the E. coli enzyme. The electronic properties of the coupled [Fe4S4]-sirohaem redox centre common to both nitrite- and sulphite-reducing enzymes are apparently strongly dependent on the environment generated by protein side chains.

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Proton NMR study of the interaction of tin(IV) protoporphyrin IX monomers and dimers with apomyoglobin

Deeb¹,

Peyton²

1992

Biochemistry

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Events during the reconstitution of apomyoglobin to form the holoprotein were probed by porphyrin-metal substitution. Thus interactions between tin(IV) protoporphyrin IX (SnPP) and equine apomyoglobin (apoEqMb), and between tin(IV) protoporphyrin IX dimers [(SnPP)2] and apoEqMb, were observed by 1H NMR and optical absorbance spectroscopic techniques. The chief advantages of using SnPP are that products and intermediates can easily be related to SnPP.EqMb which has been studied [Deeb, R.S., & Peyton, D.H. (1991) J. Biol. Chem. 266, 3728-3733] and that at least one step during reconstitution is slowed considerably as compared to heme. Reactions of apoEqMb with SnPP and (SnPP)2 produce different intermediates, although the final product, SnPP.EqMb, is the same for each. An intermediate observed for reaction of SnPP with apoEqMb at pH 10 is in exchange with free SnPP, with the observed rate constant koff approximately 1 s-1. meso-Proton resonances were assigned for this intermediate by correlation to SnPP resonances via chemical exchange. The intermediate observed for reaction of (SnPP)2 with apoEqMb at pH 7.5 is heterogeneous. The reaction of either SnPP or (SnPP)2 with apoEqMb at neutral pH produces another species which may be the alternate porphyrin-insertion isomer arising from a 180 degree rotation about the alpha, gamma-meso axis of the porphyrin. Although optical absorbance spectroscopy of the Soret region shows evidence for each reaction, only in combination with 1H NMR are the various processes assigned.

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Heme rotational isomerism is not required for the production of Q-band splitting in the spectra of iron-porphyrin proteins

Cited by 4 publications

References 4 publications

Spectral Splitting in the α (Q_0,0) Absorption Band of Ferrous Cytochrome c and Other Heme Proteins

Spectral Splitting in the α (Q_0,0) Absorption Band of Ferrous Cytochrome c and Other Heme Proteins

Electronic properties of the dissimilatory sulphite reductase from Desulfovibrio vulgaris (Hildenborough): comparative studies of optical spectra and relative reduction potentials for the [Fe4S4]-sirohaem prosthetic centres

Proton NMR study of the interaction of tin(IV) protoporphyrin IX monomers and dimers with apomyoglobin

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Heme rotational isomerism is not required for the production of Q-band splitting in the spectra of iron-porphyrin proteins

Cited by 4 publications

References 4 publications

Spectral Splitting in the α (Q0,0) Absorption Band of Ferrous Cytochrome c and Other Heme Proteins

Spectral Splitting in the α (Q0,0) Absorption Band of Ferrous Cytochrome c and Other Heme Proteins

Electronic properties of the dissimilatory sulphite reductase from Desulfovibrio vulgaris (Hildenborough): comparative studies of optical spectra and relative reduction potentials for the [Fe4S4]-sirohaem prosthetic centres

Proton NMR study of the interaction of tin(IV) protoporphyrin IX monomers and dimers with apomyoglobin

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Spectral Splitting in the α (Q_0,0) Absorption Band of Ferrous Cytochrome c and Other Heme Proteins

Spectral Splitting in the α (Q_0,0) Absorption Band of Ferrous Cytochrome c and Other Heme Proteins