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Structural-changes in cytochrome-c upon hydrogen-deuterium exchange
Citation key ISI:A1993MP28300013
Author Hildebrandt, P and Vanhecke, F and Heibel, G and Mauk, A G
Pages 14158-14164
Year 1993
ISSN 0006-2960
Address 1155 16TH ST, NW, WASHINGTON, DC 20036
Journal Biochemistry
Volume 32
Number 51
Month DEC 28
Publisher AMER CHEMICAL SOC
Abstract The resonance Raman spectra of yeast ferri- and ferro-iso-1-cytochrome c dissolved in H2O and D2O are reported. Hydrogen exchange in the protein leads to distinct spectral changes of heme vibrational bands, particularly in the region between 670 and 710 cm-1 and at approximately 443 and approximately 450 cm-1. The latter two bands, which have previously been assigned to porphyrin modes including bending vibrations of the propionate side chains [Hildebrandt, P. (1991) J. Mol. Struct, 242, 379-395], reveal frequency shifts by up to 4 cm-1. These shifts are attributed to structural changes of the propionate groups caused by the energetic differences of the hydrogen and deuterium bonds between these substituents and the adjacent amino acid residues. The frequency shifts of the bands between 670 and 710 cm-1 most likely reflect structural differences of the tetrapyrrole macrocycle itself. Time-dependent experiments revealed that the hydrogen exchange processes associated with the changes in the resonance Raman spectra are complete in less than 15 min. The protons which are involved are those in the interior of the heme pocket as concluded by comparison with the exchange rate constants previously determined by NMR spectroscopy [Mayne, L., Paterson, Y., Cerasoli, D., & Englander, S. W. (1992) Biochemistry 31, 10678-10685]. These protons are part of a hydrogen bonding network including the amide protons of Asn-52, Met-80, and Lys-79, the side chain protons of Asn-52, Tyr-67, Thr-78, Trp-59, and Thr-49, and the water molecules 121 and 166. The subtle alterations of the hydrogen bonding interactions which are induced by hydrogen-deuterium exchange are apparently sufficient to cause structural changes in the heme which are detected by the resonance Raman spectrum. The present results demonstrate that the hydrogen bonding network in the heme pocket of cytochrome c sensitively controls the conformation of the porphyrin.
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