[Leslie Carol Botha: Cycles and biological clocks dance to the rhythm of the Universe. Our health, physical and mental is directly tied to dancing this dance.]
Biological clock began ticking 2.5 billion years ago
16 May 2012 by Debora MacKenzie
Our core physiology relies on subtle organic timers: disrupt them, and effects range from jet lag to schizophrenia. Exactly how and when life began keeping time is unclear, but a candidate for the original biological clock may solve the mystery.
Biological clocks are ubiquitous in nature, so the first clock should pre-date the evolutionary parting of the ways that led to modern groups of organisms. All the clocks found so far are unique to different groups of organisms, though. Not so the clock discovered by Akhilesh Reddy at the University of Cambridge and colleagues. In an enzyme called peroxiredoxin (PRX), they seem to have found a grandfather clock – one that is common to nearly all life.
PRX gets rid of poisonous, highly reactive oxygen (ROS), which is produced by oxygen-based metabolism. And the enzyme oscillates: it flits between an active and inactive state, depending on whether oxygen is bound to the active site. Using antibodies that bind only to the oxidised enzyme, the team found that PRX oxidation keeps cycling independently on a 24-hour cycle, even when organisms were kept in constant light or constant dark.
Reddy thinks PRX protected primitive cells from ROS damage by surging when peaks in photosynthesis related to daylight temporarily bumped up levels of oxygen. “Initially this was externally driven,” he says. Then PRX began oscillating spontaneously in anticipation of this load – thus becoming an independent daily clock. “Organisms with this anticipatory ability would be better adapted than organisms that merely ‘reacted’ to things as they happened,” Reddy says.
Moreover, they found this PRX cycle in mice, fruit flies, a plant, a fungus, an alga, bacteria and even in archaea – the most primitive of all cellular life (Nature, DOI: 10.1038/nature11088). That suggests PRX evolved early in life’s history. A gene sequence analysis suggests it did so 2.5 billion years ago, during the Great Oxygenation Event (GOE) – a critical interval when the oxygen released by photosynthesis began to accumulate in the atmosphere.