Brian R. Crouse

Spectroscopic identification of the axial ligands of cytochrome b560 in bovine heart succinate-ubiquinone reductase

The axial ligands of low potential cytochrome b 560 in the five subunit bovine heart succinate‐ubiquinone reductase complex and in the isolated quinone binding proteins have been investigated using EPR and near‐infrared magnetic circular dichroism spectroscopies. The results are consistent with bis‐histidine ligation with near‐perpendicular imidazole rings for cytochrome b 560 in the four‐subunit complex. The pronounced changes in EPR properties that accompany isolation of the cytochrome‐b 560 containing quinone binding proteins, are attributed to perturbation of the orientation of the imidazole rings of the heme bis‐histidine ligands, rather than a change in axial ligation.

Spectroscopic identification of the heme axial ligation of cytochrome b558 in the NADPH oxidase of porcine neutrophils

The combination of electron paramagnetic resonance (EPR), near‐infrared magnetic circular dichroism (NIR‐MCD) and resonance Raman (RR) spectroscopies at cryogenic temperatures has been used to identify the axial heme ligation of the low spin cytochrome b 558 component of NADPH oxidase from porcine blood neutrophils. The EPR and NIR‐MCD results indicate the presence of two distinct forms in frozen solution; one with a low field g‐value at 3.23 and porphyrin(π)‐to‐Fe(III) charge transfer maximum at 1660 nm and the other a low field g‐value at 3.00 and porphyrin(π)‐to‐Fe(III) charge transfer maximum at 1510 nm. On the basis of these properties and the RR studies, both are attributed to forms of cytochrome b 558 with bis‐histidine axial ligation. The origin of the observed heterogeneity, the location and identity of the specific histidines involved in ligating the heme, and the role of the heme prosthetic group in O2 − production are discussed in light of these results.

Spectroscopic Properties and Molecular Structure of 1,3-Dimethyl-2-(Se, Se-dibromoseleno)-2(3H)-imidazolylidene

Oxidative addition of Br2 to 1,3-dimethyl-2(3H)-imidazoleselone results in a compound that can be viewed as a Se(II) bromide complex with a stabilized imidazolylidene ring as verified by X-ray crystallography. The structure consists of dimeric pairs containing nearly linear Br-Se-Br units bonded through carbon to planar imidazolyidene rings at torsion angles of 91.4° for N1-C1-Se1-Br1 and 76.8° for N3-C6-Se2-Br4. Significant intermolecular contacts between dimeric units are seen through short Se–Se [3.494(1) A] and Se1–Br4 bridging [3.509(1) A]. Solution state Raman data show the characteristic peaks for a linear Br-Se-Br moiety with a strong polarized peak at 158 cm−1 and a weak shoulder at 181 cm−1 corresponding to the symmetric and asymmetric Br-Se-Br stretching modes respectively. In the absence of X-ray data, correlation of structure to vibrational data provides further support for structural speculations in other compounds with the linear SeBr2 grouping. Crystal structure data for C5H8N2Br2Se. Cell ...