A novel, anaerobically induced ferredoxin in Chlamydomonas reinhardtii

We have found the transcript of one of at least six ferredoxin encoding genes of the green alga Chlamydomonas reinhardtii , FDX5 , strongly accumulating in anaerobiosis, indicating a vital role of the encoded protein in the anaerobic metabolism of the cells. According to absorption and electron paramagnetic resonance spectroscopy, Fdx5 is a plant‐type [2Fe2S]‐ferredoxin with a redox potential similar to that of the ferredoxin PetF. However, although Fdx5 seems to be located in the chloroplast, it is not able to photoreduce nicotinamide adenine dinucleotide phosphate (NADP + ) via ferredoxin‐NADP‐reductase, nor to be an electron donor to the plastidic [FeFe]‐hydrogenase HydA1. Thus, Fdx5 seems to have a special role in a yet to be identified anaerobic pathway.