Relationship between cardiolipin content and cytochrome c oxidase activity of cytochrome aa3 in Paracoccus denitrificans.

Using cultivation at different oxygen tensions, the molar ratio of cardiolipin to haem a in cells of Paracoccus denitrificans was varied systematically from 30 to 300. The molecular activity of cytochrome aa3 (with N, N, N', N'-tetramethyl-p-phenylenediamine as substrate) remained unchanged in this interval, this ruling out any regulatory effect of physiological cardiolipin levels on the terminal oxidase. Titration of anaerobically grown cells with cyanide indicated the presence of cytochrome aa3 which accounted for about 1/4 of the total electron flow from TMPD to oxygen.