When green algae "can't breathe," they get rid of excess energy through the production of hydrogen. Biologists at the Ruhr-Universität Bochum in Germany have found out how the cells notice the absence of oxygen. For this, they need the messenger molecule nitric oxide and the protein hemoglobin, which is commonly known from red blood cells of humans. With colleagues at the UCLA, the Bochum team reported its results online on June 10, 2013 in PNAS. In the human body, hemoglobin transports oxygen from the lungs to the organs and brings carbon dioxide, which is produced there, back to the lungs. "However, scientists have known for years that there is not just the one hemoglobin," says Professor Thomas Happe from the Work Group Photobiotechnology. Nature has produced a large number of related proteins which fulfill different functions. The green alga Chlamydomonas reinhardtii has what is known as a "truncated" hemoglobin, the function of which was previously unknown. Dr. Happe's team has deciphered its role in surviving in an oxygen-free environment. When Chlamydomonas has no oxygen available, the algae transfer excess electrons to protons, creating hydrogen (H2). "For this to work, the green alga activates a certain gene program and creates many new proteins," Dr. Happe explains. "But how exactly the cells even notice that oxygen is missing is something we did not know." The research team looked for genes that are particularly active when green algae have to live without oxygen – and found a gene that forms the blueprint for a hemoglobin. In an oxygen-rich environment, however, this gene was completely idle. The scientists studied the hemoglobin protein and its genetic blueprint in more detail using molecular biological and biochemical analyses. "One thing became clear very quickly," says Dr.
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