Structural study of the heme crevice in cytochrome [formula omitted] based on individual assignments of the 1H-NMR lines of the heme group and selected amino acid residues

Abstract

Measurements of saturation transfer, spin-decoupling and truncated-driven nuclear Overhauser effect difference spectra were applied to individually assign the 1H-NMR lines of the heme group and nearby amino acid residues in reduced and oxidized cytochrome b 5 . These data imply that the orientation of the heme group in the major cytochrome b 5 conformation in solution differs from that reported for the X-ray crystal structure by a 180° rotation about an axis through the meso-carbon atoms α and γ. Otherwise comparison of the experimental chemical shifts with those obtained from ring current calculations using the refined X-ray atomic coordinates provide no evidence that the polypeptide conformation near the heme is different in the crystals and in solution. It seems quite likely that the previously described second solution conformation of cytochrome b 5 is related to the major species through a different orientation of the heme.