Resonance Raman studies of Escherichia coli sulfite reductase hemoprotein. 2. Fe sub 4 S sub 4 cluster vibrational modes

• Published in: Biochemistry (Easton) 1989-06, Vol.28:13
• Main Authors: Madden, J.F., Siegel, L.M., Han, Sanghwa, Spiro, T.G.
• Format: Article
• Language: English
• Subjects: 550601 - Medicine- Unsealed Radionuclides in Diagnostics; BACTERIA; ESCHERICHIA COLI; EVEN-EVEN NUCLEI; IRON COMPOUNDS; ISOTOPES; LASER SPECTROSCOPY; LIGANDS; LIGHT NUCLEI; METALLOPROTEINS; MICROORGANISMS; MOLECULAR STRUCTURE; NUCLEI; ORGANIC COMPOUNDS; OXYGEN COMPOUNDS; PROTEINS; RADIOLOGY AND NUCLEAR MEDICINE; RAMAN SPECTROSCOPY; SPECTRAL SHIFT; SPECTROSCOPY; STABLE ISOTOPES; SULFITES; SULFUR 34; SULFUR COMPOUNDS; SULFUR ISOTOPES; TRANSITION ELEMENT COMPOUNDS
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi00439a023

Resonance Raman (RR) spectra from the hemoprotein subunit of Escherichia coli sulfite reductase (SiR-HP) are examined in the low-frequency (200-500 cm{sup {minus}1}) region where Fe-S stretching modes are expected. In spectra obtained with excitation in the siroheme Soret or Q bands, this region is dominated by siroheme modes. Modes assignable to the Fe{sub 4}S{sub 4} cluster are selectively enhanced, however, with excitation at 488.0 or 457.9 nm. The assignments are confirmed by observation of the expected frequency shifts in SiR-HP extracted from E. coli grown on {sup 34}S-labeled sulfate. The mode frequencies and isotopic shifts resemble those seen in RR spectra of other Fe{sub 4}S{sub 4} proteins and analogues, but the breathing mode of the cluster at 342 cm{sup {minus}1} is higher than that observed in the other species. Spectra of various ligand complexes of SiR-HP reveal only slight sensitivity of the cluster terminal ligand modes to the presence of exogenous heme ligands, at variance with a model of ligand binding in a bridged mode between heme and cluster. Close examination of RR spectra obtained with siroheme Soret-band excitation reveals additional {sup 34}S-sensitive features at 352 and 393 cm{sup {minus}1}. These may be attributed to a bridging thiolate ligand.