Abstract
Substitution of H 2 16O by H 2 17O induces a substantial broadening of the high-field line in the electron-spin resonance spectrum of ferric myoglobin due to the presence of H 2 17O at the axial ligand-site. Computer simulations of the experimental spectra yielded the values of the reciprocal relaxation time T 2 −1 = 7.8 G and the 17O-hyperfine coupling constant A = 18 ± 1 G. Under identical experimental conditions no effect of H 2 17O was observed in horseradish peroxidase. The latter finding excludes the possibility that a water molecule is liganded to the peroxidase haem-iron and supports either the idea that both axial ligands are amino acid residues or that the haem in ferric horseradish peroxidase is pentacoordinate.
Published Version
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