Analysis of field-dependent relaxation data and hyperfine shifts of cytochrome c' from Rhodospirillum rubrum in terms of the high-spin iron ligation states

Journal Article · Wed Jul 29 04:00:00 EDT 1981 · J. Am. Chem. Soc.; (United States)

DOI:https://doi.org/10.1021/ja00405a020· OSTI ID:6255779

La Mar, G N; Jackson, T; Bartsch, R G

The pH and field dependence of the paramagnetic line widths of the heme methyl resonances of cytochrome c' from Rhodospirillum rubrum (strain 1 DTCC) have been analyzed for the purpose of extracting information on the ligation states of the protein in both its oxidized and its reduced high spin forms. The methyl line widths in all protein forms were found to exhibit substantial quadratic field dependence consistent with significant contribution from Curie spin relaxation. For ferricytochrome c', the field-independent contribution to the methyl line width differed substantially between the acid-to-neutral pH form (I) and form II, stable in the pH range 9 to 11. Comparison of the calculated electron relaxation times indicates that form I has a weaker axial ligand field than either form II or aquometmyoglobin, which favors a five-coordinate I and a six-coordinate II. The appearance of two new resonances in the far downfield region upon converting I ..-->.. II, without the apparent loss of any hyperfine shifted signals from I, confirms the coordination of a sixth ligand in II. Qualitative comparisons of the line widths fo these two new signals to those of the heme methyls support an acidic residue as the sixth ligand. The detection of the characteristic exchangeable proton resonance of an axial imidazole and the importance of Curie spin relaxation in ferrocytochrome c' confirm its high-spin five-coordinated structure. 4 figures.

• Research Organization: Univ. of California, Davis
• OSTI ID: 6255779
• Journal Information: J. Am. Chem. Soc.; (United States), Journal Name: J. Am. Chem. Soc.; (United States) Vol. 103:15; ISSN JACSA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
BACTERIA
COMPLEXES
CYTOCHROMES
DATA
ELEMENTS
EXPERIMENTAL DATA
HYDROGEN
HYPERFINE STRUCTURE
INFORMATION
IRON COMPLEXES
LIGANDS
LINE WIDTHS
MAGNETIC FIELDS
MAGNETIC RESONANCE
MICROORGANISMS
NONMETALS
NUCLEAR MAGNETIC RESONANCE
NUMERICAL DATA
PH VALUE
PIGMENTS
RESONANCE
RHODOSPIRILLUM
TRANSITION ELEMENT COMPLEXES