Open AccessProton Magnetic Resonance Studies of the Ferredoxins from Spinach and Parsley
Author(s) -
Martin Poe,
William D. Phillips,
Jerry D. Glickson,
C. C. McDonald,
Anthony San Pietro
Publication year - 1971
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.011
H-Index - 771
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.68.1.68
Subject(s) - ferredoxin , spinach , chemistry , electron paramagnetic resonance , redox , unpaired electron , crystallography , diamagnetism , chemical shift , sulfur , valence (chemistry) , nuclear magnetic resonance , inorganic chemistry , magnetic field , biochemistry , physics , organic chemistry , enzyme , quantum mechanics
Contact-shifted resonances have been detected in the pmr spectra of both oxidized and reduced forms of spinach and parsley ferredoxins. These resonances are assigned to the β-CH2 protons of four cysteine residues that are thought to bind the iron-sulfur redox center to the polypeptide chain. Temperature dependences of contact shifts reveal that the two iron atoms are antiferromagnetically coupled in both redox forms of each of these proteins. Thermal population of magnetic states gives rise to the contact shifts observed in the formally diamagnetic oxidized forms of these ferredoxins and accounts for the failure of contact shifts in the reduced forms exhibit to a Curie Law temperature dependence. It appears that the unpaired electron of reduced spinach and parsley ferredoxin is unequally distributed over the two iron centers. Valence states for the iron pairs of high-spin Fe+3 -Fe+3 and Fe+2 -Fe+3 for the oxidized and reduced forms, respectively, are compatible with the nmr results.