EPR signals of redox active copper in EDTA washed membranes of the cyanobacterium Synechococcus 6311.

A signal of Cu2+ (g = 2.03) was detected by electron paramagmetic resonance spectroscopy in oxidized membrane preparations of Synechococcus 6311. The membranes were prepared and washed in the presence of EDTA (10mM, pH 8.0) and, hence, were depleted of adventitious copper; the treatment also would remove any membrane-associated soluble redox proteins and other paramagnetic metal ions. 0.1% Triton X-100 facilitated detection of the Cu2+ signal which was fully reduced by dithionite or ascorbate plus N,N,N',N',-tetramethyl-p-phenylenediamine, and partially reduced NADPH and NADH, which are known to donate electrons to the terminal oxidase of cyanobacteria via the respiratory chain. Using temperature dependence and power saturation of the EPR copper signal, we conclude that copper is a firmly bound constituent of the terminal oxidase in an environment which is very similar if not identical to other cytochrome c oxidase preparations.