SPECTROSCOPIC INVESTIGATIONS ON THE WATER-SOLUBLE FRAGMENT OF THE RIESKE [2FE-2S] PROTEIN FROM PARACOCCUS-DENITRIFICANS

A large-scale purification procedure has been developed to isolate the membrane-bound bc(1) complex of Paracoccus denitrificans. From the pu rified complex, a water-soluble fragment has been isolated. The fragme nt comprising residues 50-190 contains the Rieske [2Fe-2S] cluster and has an optical spectrum which is typical of such a cluster. The EPR s pectrum of the cluster in the bc(1) complex differs slightly from the spectrum of the water-soluble fragment. Differences in the g values an d linewidths of the resonances can be attributed to the absence of bou nd quinone in the water-soluble fragment. Signals from the cysteines a nd histidines that coordinate to the [2Fe-2S] cluster could be identif ied in the H-1 NMR spectrum of the fragment in solution. (C) 1998 Else vier Science S.A. All rights reserved.