Open Access1 H‐ and 13 C‐NMR investigation of redox‐state‐dependent and temperature‐dependent conformation changes in horse cytochrome c
Author(s) -
TURNER David L.,
WILLIAMS Robert J. P.
Publication year - 1993
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1993.tb17582.x
Subject(s) - chemistry , chemical shift , redox , diamagnetism , crystallography , cytochrome c , electron transfer , proton nmr , nmr spectra database , nuclear magnetic resonance , spectral line , stereochemistry , photochemistry , inorganic chemistry , magnetic field , biochemistry , physics , quantum mechanics , astronomy , mitochondrion
The redox‐state dependent changes in chemical shift, which have been measured for almost 100 CH n groups in the 13 C‐NMR spectra of horse cytochrome c [Santos, H., and Turner, D. L. (1992) Eur. J. Biochem. 206 , 721–728], have been used to investigate the nature of the redox‐related change in conformation. Apart from the haem and its axial ligands, the shifts are found to be dominated by the electron–nuclear dipolar coupling in the oxidised form, as was the case in 1 H‐NMR studies. These pseudocontact shifts are well described by using an empirically determined magnetic susceptibility tensor in conjunction with atomic coordinates for the horse cytochrome c. The groups which fit least well are located in the vicinity of Trp59. Comparison between 1 H and 13 C shifts and their temperature dependence shows that the differences from expectation based on a single structure for both oxidation states are caused largely by changes in the diamagnetic contribution to the chemical shifts. Since these are different for 1 H and 13 C resonances they indicate, independently from crystal structure data, some redox‐related movement of the protein under the haem. The significance of these results for understanding electron transfer pathways is discussed. Finally, the temperature dependence of the pseudocontact shifts in the range 30–50°C is shown to be anomalous. Approximately half of the anomalous effect may be attributed to Zeeman mixing of the electronic wavefunctions with a spin‐orbit coupling constant γ– 241 cm −1 , while the other half is attributed to thermal expansion of the protein.