Identification of mitochondrial respiratory proteins from the green alga Chlamydomonas reinhardtii.

Membrane preparations from the green alga Chlamydomonas reinhardtii contain both thylakoid and mitochondrial membranes [1]. These preparations have been intensely used to study the structure, function and biogenesis of protein complexes involved in the photosynthetic pathway. We show here that these preparations are also suitable for studying protein complexes of the mitochondrial respiratory chain of the alga. The respiratory complexes, fractionated on a sucrose gradient in the presence of Triton X-100, were identified by their catalytic properties and their polypeptide content. From the bottom to the top of the sucrose gradient, we identified the NADH: ubiquinone oxidoreductase (complex I), the mitochondrial ATP synthase (F0F1-ATPase), the cytochrome bc1 complex and the cytochrome c oxidase. At the top of the gradient, another enzyme was detected which displayed an NADH: menaquinone oxidoreductase activity.