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 assignme nt was available. The hyperfine shifts of the alpha and beta carbons o f the coordinated cysteines, as well as those of their attached proton s, have been discussed in terms of the current magnetic coupling model s and of the mechanisms of spin density delocalization. Through HSQC s pectra preceded by a proton 180 degrees pulse, the nonselective T-1 va lues of the protons have been accurately obtained. It is shown how the nuclear T-1 values can be used as constraints, together with NOEs, fo r solution structure determination even when the present magnetic coup ling scheme occurs. The oxidized cluster is shown to have an effective relaxation time much shorter than that in the reduced state.