Occurrence of cytochrome aa3 in Anacystis nidulans

The cytochrome content of membrane fragments prepared from the blue-green alga (cyanobacterium) Anacystis nidulans was examined by difference spectrophotometry. Two beta-type cytochromes and hitherto unknown cytochrome alpha could be characterized. In the reduced-minus-oxidised difference spectra the alpha-type cytochrome showed an alpha-band at 605 nm and a gamma-band at 445 nm. These bands shifted to 590 and 430 nm, respectively, in CO difference spectra, NADPH, NADH and ascorbate reduced the cytochrome through added horse heart cytochrome c as electron mediator. In presence of KCN the reduced-minus-oxidised spectrum showed a peak at 600 nm and a trough at 604 nm. Photoaction spectra of O2 uptake and of horse heart cytochrome c oxidation by CO-inhibited membranes showed peaks at 590 and 430 nm. These findings are consistent with cytochrome aa3 being the predominant respiratory cytochrome c oxidase in Anacystis nidulans.