Taenia crassiceps metacestodes have cytochrome oxidase aa3 but not cytochrome o functioning as terminal oxidase

In mitochondria obtained from Taenia crassiceps metacestodes, carbon monoxide difference spectra reveal signals characteristic of the classical mitochondrial oxidase, cytochrome aa3, as well as signals suggesting the presence of 'cytochrome o'. In the present work, using photodissociation spectrophotometry and analysis of the haem groups, we conclude that there is no haem O in these larvae, and that the only cytochrome that functions as terminal oxidase is cytochrome c oxidase, aa3. At temperatures between -70 and -100 degrees C, the energy of activation for CO reassociation with cytochrome a3 was 10.5 kcal x mol(-1), and for oxygen binding 7.8 kcal x mol(-1).