Different reactivity of carboxylic groups of cytochrome c oxidase polypeptides from pig liver and heart.

Cytochrome c oxidase isolated from pig liver and heart was incubated with 1-ethyl-3-[3-(dimethyl-amino)propyl]carbodiimide and [14C]glycine ethyl ester in the presence and absence of cytochrome c. Labelling of individual subunits was determined after separation of the enzyme complexes into 13 polypeptides by SDS-gel electrophoresis. Polypeptide II and additional but different polypeptides were labelled in the liver and in the heart enzyme. Labelling of polypeptide II and of some other polypeptides could be partially or completely suppressed by cytochrome c. From the data two conclusions can be drawn: In addition to polypeptide II, other polypeptides take part in the binding of cytochrome c to cytochrome c oxidase; the binding domain for cytochrome c is different in pig liver and heart cytochrome c oxidase.