NMR determination of the magnetic susceptibility anisotropy of cytochrome c ' of Rhodobacter capsulatus by (1)J(HN) dipolar coupling constants measurement: Characterization of its monomeric state in solution
H. Demene et al., NMR determination of the magnetic susceptibility anisotropy of cytochrome c ' of Rhodobacter capsulatus by (1)J(HN) dipolar coupling constants measurement: Characterization of its monomeric state in solution, J PHYS CH B, 104(11), 2000, pp. 2559-2569
(1)J(NH) splittings have been measured at 600 and 400 MHz on the paramagnet
ic (S = 2 and S = 5/2) and on the diamagnetic state (S = 0) of cytochrome c
' of Rhodobacter capsulatus. Residual dipolar splittings and the magnetic s
usceptibility tensor have been then derived using two methods. The first me
thod equaled for a paramagnetic species the dipolar splitting to the differ
ence of the measured (1)J(NH) splittings between the paramagnetic and diama
gnetic forms at one field. The second method consisted in deriving the tota
l magnetic tensor of the paramagnetic forms from the splittings at two fiel
ds with a post-correction for the diamagnetic contribution. Both methods ar
e shown to produce equivalent results for the determination of the suscepti
bility magnetic tensor. Comparison with the magnetic tensor obtained with a
previous study based on the dipolar shifts leads to the evidence that, unl
ike most other cytochromes c', Rb. capsulatus cytochrome c' of strain M1131
is monomeric in solution. This result is discussed in view of the cytochro
me c' function. Our study confirms that dipolar splittings sure a powerful
tool for structure determination, providing insight not only into local str
uctural details but also into the global fold of molecules.