Chlorophyll degradation in a Chlamydomonas reinhardtii mutant: An accumulation of pyropheophorbide a by anaerobiosis

Chlorophyll degradation was investigated in cells of a chlorophyll b-less mutant of Chlamydomonas reinhardtii under aerobic and anaerobic conditions. During degradation of chlorophyll under anaerobic conditions, chlorophyll catabolite P535, an open-tetrapyrrole, was not excreted, but pyropheophorbide a was accumulated as the end product with a transient accumulation of chlorophyllide a and pheophorbide a in cells, in contrast to the breakdown under aerobic conditions. It is likely that in the absence of oxygen, degradation of chlorophyll a proceeds to pyropheophorbide a by three consecutive reactions, dephytylation, metal-releasing and demethoxycarbonylation, and then stops due to a limitation of the oxygen that the monooxygenase reaction requires for bilin formation. A novel enzyme catalyzing demethoxycarbonylation of pheophorbide a was partially purified. The enzyme activity increased dependent on the age of cells, and its increase was completely suppressed by cycloheximide. Production of P535 was also dependent on cytoplasmic protein synthesis.