Models of the cytochromes b. Control of axial ligand orientation with a hindered porphyrin system

Low‐Temperature EPR and Mössbauer Spectroscopy of Two Cytochromes with His–Met Axial Coordination Exhibiting HALS Signals

“…[23] The calculated rhombic term (V) is almost equal for these two cytochromes, reflecting the structural similarities of the heme cores ( Figure 1 www.chemphyschem.org cytochrome c 552 . However, this has to be taken with care because of the high uncertainty of D. The pH-dependence of these cytochromes was followed by EPR spectroscopy.…”

pH Dependence of Structural and Functional Properties of Oxidized Cytochrome c" from Methylophilus methylotrophus

“…The two axial ligands are histidines in the oxidized form, one of which is detached from heme upon reduction of the iron atom (2). Cytochrome cЉ is a unique example of a heme-c protein with bis-histidine coordination and spectroscopic features similar to those observed in model compounds where axial ligand planes are forced into a perpendicular orientation by steric constraints (3). NMR studies of the heme pocket have shown that it is quite stable at neutral pH, with low amide proton exchange rates and one of the heme propionates largely exposed at the surface, whereas the other one is buried in the protein (1).…”

Nitric oxide interaction with insect nitrophorins and thoughts on the electron configuration of the FeNO complex

“…Formal core diagrams of the nitrophorin complexes of NP4 [101,102] and NP2 [227] have been constructed, and root-mean-square deviations (RMSD) from the mean plane, in units of 0.01 Å , are listed in Table 1, where they are compared to the values obtained for relevant model heme complexes [232][233][234][235][236][237][238][239][240][241][242][243][244][245][246][247][248]. In analyzing these data, several factors must be kept in mind: (1) Among synthetic hemes, it is known that meso-substituted metalloporphyrinates are in general more ruffled than b-pyrrole-only-substituted metalloporphyrinates [229] and (2) Fe(III) porphyrinates are usually much more ruffled than Fe(II) porphyrinates [229,236,242,243].…”

“…This complex is highly ruffled, with a RMSD of 0.232 Å [236], while the Fe(II) analog, although highly saddled, has RMSD meso-carbon displacements of only 0.01 Å [237], and thus has no ruffling component. Meso-only substituted metalloporphyrins having planar six-membered ring axial ligands in perpendicular planes, as is the case for all of the (TMP)Fe(III) bis-pyridine complexes, are highly ruffled [233,245], whereas the corresponding Fe(II) complexes, all of which have the axial pyridine ligands in parallel planes [242], are quite planar; Fe(III) porphyrinates having axial ligands in parallel planes, such as [(TMP)Fe(1-MeIm) 2 ] + and [(OEP)Fe(4-NMe 2 Py) 2 ] + , are also quite planar [233]. Iron(III) dodecasubstituted porphyrin complexes such as the octaalkyltetraphenylporphyrins, which have both meso-and b-pyrrole substituents, are highly saddled, irrespective of axial ligand(s) or coordination number, but often have a ruffling component as well [246,247,258].…”