FORMATION AND PROPERTIES OF A STABLE HIGH-POTENTIAL COPPER-IRON-SULFUR CLUSTER IN A FERREDOXIN

A ferredoxin isolated from Desulfovibrio africanus contains a [3Fe-4S] cluster that reversibly binds a copper atom, yielding a stable produc t with a greatly increased reduction potential. The reaction is readil y detected in protein molecules adsorbed as a film on an electrode sur face. Electron paramagnetic resonance (EPR) and magnetic circular dich roism (MCD) spectra of oxidized and reduced bulk solution products sup port their assignment as [Cu3Fe-4S](2+) (S=1/2) and [Cu3Fe4S](1+) (S=2 ) respectively with copper bound formally as Cu(I). Cyanide causes sel ective loss of copper and regeneration of the [3Fe-4S] reactant. The r esults demonstrate the chemical feasibility of CuFeS clusters and sugg est that they could exist naturally in biological systems.