H-1 and C-13 NMR studies of an oxidized HiPIP

H-1-C-13 HETCOR NMR spectra have been recorded for the oxidized HiPIP I from Ectothiorhodospira halophila for which an extended H-1 assignment was available. The hyperfine shifts of the alpha and beta carbons of the coordinated cysteines, as well as those of their attached protons, have been discussed in terms of the current magnetic coupling models and of the mechanisms of spin density delocalization. Through HSQC spectra preceded by a proton 180 degrees pulse, the nonselective T-1 values of the protons have been accurately obtained. It is shown how the nuclear T-1 values can be used as constraints, together with NOEs, for solution structure determination even when the present magnetic coupling scheme occurs. The oxidized cluster is shown to have an effective relaxation time much shorter than that in the reduced state.