A research team has discovered that mammalian cells not only breathe in oxygen, but also respire sulfur contained in food, it has been learned.
The team, which includes Tohoku University professor Takaaki Akaike, released its findings in the British science journal "Nature Communications" on Oct. 27.
It had long been assumed that sulfur respiration was a function performed only by primitive-era cells, and that it faded out due to evolution.
However, it is now understood that sulfur respiration is essential for even humans to sustain life.
At the cellular level, respiration is a function that creates energy. The mitochondria inside the cells of living things create and use energy that is mainly drawn from glucose and oxygen.
After carefully examining both human and mouse mitochondria, the research team found that the amino acid, cysteine, and sulfur bind together and become activated due to enzymes, before going on to create energy. The team noted that the mice which were unable to perform sulfur respiration ended up with a shortened lifespan of about 10 days.
Unlike oxygen, sulfur is not something that is constantly absorbed from outside. It is thought that sulfur contained in food is recycled and then used inside the body after it is ingested. Bodily parts such as the heart and bone marrow, which require a lot of oxygen, are prone to oxygen deficiency -- and this is apparently compensated for through sulfur respiration.
When there was no oxygen on Earth more than 3 billion years ago, it is thought that ancient bacteria performed sulfur respiration in order to gain energy. Commenting on the history of sulfur respiration, Akaike said: "I'm surprised to discover that the respiratory systems of ancient organisms, which had been forgotten about, had been used all this time."