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Hemoglobin Structural Dynamics as Monitored by Resonance Raman Spectroscopy
Author(s) -
Spiro Thomas G.
Publication year - 1981
Publication title -
israel journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.908
H-Index - 54
eISSN - 1869-5868
pISSN - 0021-2148
DOI - 10.1002/ijch.198100020
Subject(s) - chemistry , porphyrin , heme , resonance raman spectroscopy , raman spectroscopy , photodissociation , resonance (particle physics) , photochemistry , imidazole , electron paramagnetic resonance , intersystem crossing , excited state , ligand (biochemistry) , relaxation (psychology) , crystallography , hemeprotein , nuclear magnetic resonance , stereochemistry , singlet state , atomic physics , psychology , social psychology , biochemistry , physics , receptor , optics , enzyme
Resonance Raman spectra of the heme group are now understood at a level sufficient to provide a useful monitor of several heme structural features. Some porphyrin vibrational frequencies are sensitive to Fe oxidation state, or π‐electron distribution, and give insight into the electronic structure of 0 2 , CO and NO hemes. Others are sensitive to Fe spin‐state, via the associated geometry variation, and provide an accurate index of the porphyrin core size. When examined during the photolysis of CO‐hemoglobin via short laser pulses, these frequencies indicate that conversion from low‐ to high‐spin Fe 11 takes place within 30 ps of photolysis, presumably via intersystem‐crossing in the excited state, but that the subsequent relaxation of the Fe atom out of the heme plane takes longer than 20 ns, probably because of restraint by the protein. Axial ligand modes have been identified for several heme derivatives. The Fe‐imidazole frequency in deoxyhemoglobin is appreciably lowered in the T quaternary structure, as determined in both static and kinetic experiments, suggesting molecular tension or proximal imidazole H‐bond weakening in the T state.