Ellipticity of cytochrome alpha3 and rotational mobility of cytochrome c-oxidase in the cristae membrane of mitochondria.

Cytochrome mediates the step in respiratory chain. accepts electrons by one cytochrome c accumulates four equivalents until finally reduces The reducing reside on hemes (cyto(I and u3, resp.) on two There is evidence that electron transfer cytochrome c oxygen crosses cristae membrane mitochondria whereby contributes the electric generation (for review, see [ 1 ] ). The orientation of the two hemes relative to the cristae membrane and the rotational mobility of the whole enzyme is subject to current studies [2,3]. A previous paper [2] reported on the polarized flash photolysis of the complex formed between cytochrome a3 and Co. The linear dichcoism of the resulting absorption changes was analysed to yield information on heme symmetry and rotational mobility of the enzyme. At a given wavelength pair of excitation (585 nm) and of observation (445 nm), a dichroic ratio of about 413 was observed, which was interpreted as indicative of an ‘effective’ 4-fold symmetry of the n-electron system in cytochrome a3. To account for the fact that the same dichroic ratio resulted for the isolated and immobilized enzyme as well as for the enzyme in mitochondria, two alternative interpretations were given: (a) Either cytochrome-c-oxidase is completely immobilized within the cristae membrane, or (b) it carries out only uniaxial Brownian rotation with the rotation axis in parallel to the symmetry axis of the heme (normal to the heme plane).