: A small, type 1 blue copper protein has been isolated from the green photosynthetic bacterium Chloroflexus aurantiacus. This protein, named auracyanin, appears to be peripherally associated with the cytoplasmic membrane, with a midpoint potential of +240 mV and a molar extinction coefficient of e596= 2900 M-1cm-1. Auracyanin is isolated as a disulfide-bridged dimer with a monomer molecular mass of 12 800 Da. The isoelectric point of auracyanin is 4.0. ESR spectra exhibit rhombic distortion and give no indication of interaction between the coppers. The function of auracyanin is not yet known, although its redox properties are compatible with a role in photosynthetic and/or respiratory electron flow.
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