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Title
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Characterization of the haem environment in Methylophilus methylotrophus ferricytochrome c" by 1H-NMR.
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Authors
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H.S.Costa,
H.Santos,
D.L.Turner.
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Ref.
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Eur J Biochem, 1993,
215,
817-824.
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PubMed id
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Abstract
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Two-dimensional NMR techniques have been used to assign proton resonances in the
haem cavity of Methylophilus methylotrophus cytochrome c", a monohaem protein
with bis-histidinyl ligation which has been shown to couple electron and proton
transfer. All the assignments were made directly for the oxidized paramagnetic
form of the cytochrome. Nearly all of the haem protons (90%) and the protons of
both axial ligands have been assigned; the side-chain protons from four other
residues in the haem pocket have also been identified. The data indicate a
highly symmetric unpaired-electron distribution in the haem group, which agrees
with a perpendicular orientation of the axial imidazole planes. The two haem
propionate groups have contrasting degrees of exposure to the solvent, with the
propionate group at position 13 being highly exposed. To obtain information on
the dynamics of the haem environment, measurements of the 1H/2H-exchange rates
of amide protons located in the haem cavity were performed. The two faces of the
haem are found to differ markedly with respect to water accessibility. All of
this information, together with additional protein sequencing data, indicates
that His52 remains attached upon reduction and that the redox-linked protonation
occurs via a channel running through the haem cleft on the opposite face.
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