Energy and Electron Transfer Systems of Chlamydomonas reinhardi. I. Photosynthetic and Respiratory Cytochrome Systems of the Pale Green Mutant.

The role of cytochromes in photosynthetic electron transfer system has been studied using the pale green mutant of Chlamydomonas reinhardi (ATCC 18302). The existence of cytochromes b(563) and f is confirmed, while no significant amount of ascorbate-reducible cytochrome b(559) is detected in this mutant. The presence of cytochrome c and a small amount of a-type cytochrome is determined in these cells.Light-induced oxidation of cytochrome b(563) is eliminated by oxygen-induced oxidation, and oxygen-induced oxidation is greatly diminished under illumination. Antimycin A diminishes the oxygen-induced oxidation of cytochrome b(563), but does not affect light-induced oxidation. In the aerobic state in the presence of 2-heptyl-4-hydroxyquinoline-N-oxide, cytochrome b(563) is reduced by illumination with far red light; this reduction is not inhibited by 3-(4'-chlorophenyl)-1,1-dimethylurea.A tentative scheme for the electron transfer system in chloroplasts, which involves a cyclic pathway via cytochrome b(563) and its interaction with oxygen, is proposed.