NDLI: The electronic structure of Fe2+ in reaction centers from Rhodopseudomonas sphaeroides. I. Static magnetization measurements.

Content Provider	PubMed Central
Author	Butler, W. F. Johnston, D. C. Shore, H. B. Fredkin, D. R. Okamura, M. Y. Feher, G.
Abstract	We have measured the static magnetization of unreduced and reduced reaction centers that vary in their quinone content. Measurements were performed in the temperature range 0.7 degrees K less than T less than 200 degrees K and magnetic fields of up to 10 kG. The electronic g-value, crystal field parameters D, E, and the exchange interaction, J, between the quinone spin and Fe2+ were determined using the spin Hamiltonian formalism. The effective moment mu eff/Fe2+ of both reduced and unreduced samples were determined to be 5.35 +/- 0.15 Bohr magnetons. This shows, in agreement with previous findings, that Fe2+ does not change its valence state when the reaction centers are reduced. Typical values of D congruent to +5 cm-1 and E/D congruent to 0.27 are consistent with Fe being in an octahedral environment with rhombic distortion. The values of D and E were approximately the same for reaction centers having one and two quinones. These findings imply that quinone is most likely not a ligand of Fe. The Fe2+ and the spin on the quinone in reduced reaction centers were found to be coupled with an exchange interaction 0 less than /J/ less than 1 cm-1. The validity of the spin Hamiltonian was checked by using an orbital Hamiltonian to calculate energy levels of the 25 states of the S = 2, L = 2 manifold and comparing the magnetization of the lowest five states with those obtained from the spin Hamiltonian. Using the orbital Hamiltonian, we calculated the position of the first excited quintet state to be 340 cm-1 above the ground state quintet. This is in good agreement with the temperature dependence of the quadrupole splitting as determined by Mossbauer spectroscopy.
Related Links	http://dx.doi.org/10.1016/s0006-3495(80)85030-2
Ending Page	992
Page Count	26
Starting Page	967
File Format	PDF
ISSN	00063495
e-ISSN	15420086
Journal	Biophysical Journal
Issue Number	3
Volume Number	32
Language	English
Publisher Date	1980-12-01
Access Restriction	Open
Subject Keyword	Biophysics Research in Higher Education
Content Type	Text
Resource Type	Article
Subject	Biophysics

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