REDUCTION OF CUA INDUCES A CONFORMATIONAL CHANGE IN CYTOCHROME-C-OXIDASE FROM PARACOCCUS-DENITRIFICANS

Cytochrome c oxidase (cytochrome aa3) from Paracoccus denitrificans contains a tightly bound manganese (II) ion, which responds to reduction of the enzyme by a change in its EPR signal (Seelig et al. (1981) Biochim. Biophys. Acta 636, 162-167). In this paper, the nature of this phenomenon is studied and the bound manganese is used as a reporter group to monitor a redox-linked conformational change in the protein. A reductive titration of the cyanide-inhibited enzyme shows that the change in the manganese EPR signal is associated with reduction of Cu(A). The change appears to reflect a rearrangement in the rhombic octahedral coordination environment of the central Mn2+ atom and is indicative of a redox-linked conformational transition in the enzyme. The managanese is likely to reside at the interface of subunits I and II, near the periplasmic side of the membrane. One of its ligands may be provided by the transmembrane segment X of subunit I, which has been suggested to contribute ligands to cytochrome a and Cu(B) as well. Another manganese ligand is a water oxygen, as indicated by broadening of the manganese EPR signal in the presence of (H2O)-O-17