J. Biol. Chem., Vol. 263, Issue 8, 3684-3689, 03, 1988
Magnetization of the oxidized and reduced three-iron cluster of Desulfovibrio gigas ferredoxin II
EP Day, J Peterson, JJ Bonvoisin, I Moura and JJ Moura
Gray Freshwater Biological Institute, University of Minnesota, Navarre 55392.
The saturation magnetizations of the three iron cluster of ferredoxin II of
Desulfovibrio gigas in both the oxidized and reduced states have been
studied at fixed magnetic fields up to 4.5 tesla over the temperature range
from 1.8 to 200 K. The low field (0.3 tesla) susceptibility of oxidized
ferredoxin II obeys the Curie law over this entire temperature range. This
establishes -2Jox greater than 200 cm-1 as the lower limit for the
antiferromagnetic exchange coupling of oxidized ferredoxin II. The
saturation magnetizations of reduced ferredoxin II at several fixed fields
yield a nested family of curves which can be fit with spin S = 2 and D =
-2.7(4) cm-1 (with E/D assigned the value 0.23 as determined by Mossbauer
and EPR spectra). The low field susceptibility of reduced ferredoxin II
also obeys the Curie law from approximately 4 up to 200 K. This establishes
-2Jred greater than 40 cm-1 as the lower limit for the antiferromagnetic
coupling of reduced ferredoxin II.