title: A comparison of the heme electronic states in equilibrium and nonequilibrium protein conformations of high-spin ferrous hemoproteins. Low temperature magnetic circular dichroism studies.
abstract: The visible and near infrared magnetic circular dichroism (MCD) spectra of equilibrium high-spin ferrous derivatives of myoglobin, hemoglobin, horseradish peroxidase and mitochondrial cytochrome c oxidase at 15 K are compared with those of the corresponding proteins in nonequilibrium conformations produced by low-temperature photodissociation of CO-complexes of these proteins as well as of O2-complexes of myoglobin and hemoglobin. Over all the spectral region (450-800 nm) the intensities of MCD bands of hemoproteins studied in equilibrium conformation are shown to be strongly temperature-dependent, including a negative band at ca. 630 nm and positive bands at ca. 690 nm and at ca. 760 nm. In contrast to the absorption spectra, the low-temperature MCD spectra of high-spin ferrous hemoproteins differ significantly, reflecting the peculiarities in the heme iron coordination sphere which are created by a protein conformation. The MCD spectra reveal clearly the structural changes in the heme environment which occur on ligand binding. On the basis of assignment of d leads to d and charge-transfer transitions in the near infrared region the correlation is suggested between the wavelength position of the MCD band at approx. 690 nm and the value of iron out-of-plane displacement as well as between the location of the band at approx. 760 nm and the Fe-N epsilon (proximal histidine) bond strength (length) in equilibrium and nonequilibrium conformations of the hemoproteins studied. The high sensitivity of low-temperature MCD spectra to geometry at heme iron is discussed.
mesh_terms: D000818:Animals; D002248:Carbon Monoxide; D002417:Cattle; D002942:Circular Dichroism; D003576:Electron Transport Complex IV; D006418:Heme; D006420:Hemeproteins; D006454:Hemoglobins; D006735:Horseradish Peroxidase; D006801:Humans; D007700:Kinetics; D008929:Mitochondria, Heart / Q000201:enzymology; D009211:Myoglobin; D011485:Protein Binding; D011487:Protein Conformation; D014907:Whales
chemical_list: D006420:Hemeproteins; D006454:Hemoglobins; D009211:Myoglobin; D006418:Heme; D002248:Carbon Monoxide; D006735:Horseradish Peroxidase; D003576:Electron Transport Complex IV