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The Origin of Breathing by Zach Zorich

Summary: The Origin of Breathing
by Zach Zorich
Some 3.5 billion years ago, a single-celled organism now named LUCA (for the Last Universal Common
Ancestor of all life on Earth) developed the ability to pull oxygen out of its environment. Although LUCA is
long gone, University of Hawaii microbiologist Maqsudul Alam has taken a step toward understanding the
secret behind this world-changing feat of chemical engineering.
LUCA evolved in an oxygen-free, or anaerobic, environment. But as oxygen levels rose in the ocean and
atmosphere, the cell had to develop a way to neutralize what was, in essence, a poison. Alam hit on that
defense while studying archaea--another type of primitive, single-celled creature. Alam studied two species
of archaea, one aerobic and the other anaerobic. He isolated a crucial compound called protoglobin that
protects anaerobic species of archaea from the toxic effects of oxygen. "Protoglobin is the nose and the
hand of the archaea," he says. "It senses oxygen, binds it, and removes it from the cell before it can do any
harm." Protoglobin, or something much like it, apparently provided a similar defense for LUCA. But that is
only half of the story. When Alam purified the protoglobin to study its structure, he saw that the molecule
looks surprisingly like diluted blood. In fact, protoglobin binds and releases oxygen the same way that
hemoglobin does as it transports oxygen through blood. Alam believes that while LUCA initially evolved
protoglobin for protection from oxygen, the organism's descendants developed a variant of the molecule--
hemoglobin--that transformed oxygen from a poison into a nutrient. That innovation enabled life to expand
into new environments and set the stage for all oxygen-breathing organisms, Alam says.


Source: Alam, Maqsudul - Department of Microbiology, University of Hawai'i at Manoa


Collections: Environmental Sciences and Ecology; Biology and Medicine