Heme a induces assembly of rat liver cytochrome c oxidase subunits I--III in isolated mitochondria.

The assembly of cytochrome c oxidase subunits I-III was studied in vitro in isolated rat liver mitochondria pre-labeled with [35S]methionine. Individual subunits were immunoabsorbed with monospecific antibodies. Isolated heme a from rat liver mitochondria, when added to radiolabeled mitochondria, induced assembly of subunit I with subunits II and III. Assembly of these subunits was not observed in mitochondria incubated in the presence of heme b(hemin) or in the absence of heme. Quantitative analysis of immunoabsorbed, radiolabeled subunits suggests that the predominant effect of heme a is on the assembly of subunit I with subunit III.