Proteolipids. V. The activity of lipid cytochrome C.
Abstract Lipid-cytochrome c prepared according to the procedure of Das and Crane 1 was found to be highly active in the transfer of electrons from ascorbate via tetramethyl- p -phenylenediamine and the cytochrome oxidase system to O 2 . The proteolipid can be assayed in aqueous medium after microdispersion by sonication. An assay method is described in detail. Lipid-cytochrome c micelles aggregate at or below pH 5.5, and the aggregate has no detectable activity. The pH optimum of lipid-cytochrome c oxidation was found at pH 6.0. High ionic strength which decomposes the lipid complex also impairs the activity. These observations are discussed in terms of the phospholipid requirements of the cytochrome-oxidase reaction.