New method for the spin quantitation of [4Fe-4S](+) clusters with S = (3)/(2). Application to the FS0 center of the NarGHI nitrate reductase from Escherichia coli.

Lanciano P, Savoyant A, Grimaldi S, Magalon A, Guigliarelli B, Bertrand P

In conventional analyses of g ≈ 5 signals given by [4Fe−4S]+ clusters with S = 3/2, the effective g values that cannot be measured in the electron paramagnetic resonance (EPR) spectrum are deduced from rhombograms calculated by assuming that the matrix is isotropic with gx = gy = gz = 2.00. We have shown that when the two low-field peaks corresponding to the Kramers doublets are visible in the spectrum, a new, independent piece of information about the system can be obtained by studying the temperature dependence of the ratio of the area under these peaks. By applying this method to the g ≈ 5 signals displayed by NarGHI nitrate reductase, we were able to determine all the parameters of the spin Hamiltonian of FS0 centers with S = 3/2 and to measure accurately their number. Our results indicate that simple analyses based on the assumption of an isotropic matrix can give rise to very large errors.


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s