While the nation ponders the robustness of a sporting foot, we might remember that the subject of animal locomotion has long fascinated the world's greatest minds. Aristotle wrote a book about it. Leonardo da Vinci filled his notebooks with observations on the flight of birds, or the anatomy of moving limbs: "The human foot is a masterpiece of engineering and a work of art."
Da Vinci tried to capture bio-mechanical principles in the design of machines, but what eluded him was the lack of an efficient means of propulsion. How birds managed to power their flight was a great puzzle. Leonardo would have been fascinated by recent research showing that the source of biological motion, and perhaps even life itself, may be one of the most mysterious phenomena known to science: quantum tunnelling.
The powerhouse of bird flight is the pectoral muscle that drives the powerful downstroke of the wing. But how do muscles generate pulling force? Living cells are able rapidly to "burn" biological fuel, to generate the energy for muscle contraction. Key players in this process are enzymes, which accelerate the rate of chemical reactions, allowing the biological fuel to be instantaneously combusted whenever our muscles need to contract.
Enzymes capture light's energy from the sun, power our cells, break down our food and synthesise all the proteins, DNA, fats and other biomolecules of living cells. They do all these jobs by speeding up chemical reactions, so that they occur on biological, rather than geological timescales. But the source of this ability to speed up reactions has eluded modern scientists. Billion-fold rate enhancements are routine: many enzymes can accelerate a chemical reaction a trillion-fold. Some of the tricks enzymes employ are pretty well understood, but not the process as a whole.
Enzymes live in the strange realm of fundamental particles, where conventional rules break down and quantum mechanics takes over. Remember Schrödinger's cat, that could exist as a weird superposition of a live and dead feline if it lived in the quantum world? Quantum mechanical particles don't have regular positions in space or time, but exist as a kind of fog of all possible positions and states. Sometimes this fog allows particles to go places or do things that would normally be prohibited, in a process called "quantum tunnelling", which is used in modern electronic devices such as tunnel diodes and is likely to be the basis of 21st-century technologies such as quantum computing.
Erwin Schrödinger, one of the founding fathers of quantum mechanics, suggested it was fundamental to life. But no one took the idea very seriously, and most 20th-century biology got on just fine without it. But 21st-century biology is delving into the structure and dynamics of biomolecules at the level of atoms, protons and electrons - and quantum effects can no longer be ignored.
Quantum rules are thought to break down and give way to the classical world as things get bigger. But enzymes are small, and move their substrate particles over short distances. David Leys, Nigel Scrutton, Michael Sutcliffe and colleagues at Manchester University, together with Adrian Mulholland at Bristol, have just published a paper in the journal Science that claims that an enzyme called aromatic amine dehydrogenase (AADH) accelerates its chemical reaction by bringing the substrate particles so close to the enzyme that the fog of particle positions overlaps, allowing a proton to "quantum tunnel" from substrate to enzyme.
That biochemical reactions involve quantum tunnelling isn't surprising, since tunnelling also happens in some inorganic reactions. But in the case of AADH, the enzyme isn't just capturing a process that occurs anyway, the dynamics of the enzyme actively promote the quantum tunnelling event in order to accelerate the reaction rate. The enzyme needs quantum mechanics to work.
Leys' research implies that enzymes have evolved to dip into the weird world of quantum mechanics to enhance reaction rates. This indicates that the motive force driving bird flight and a million other biological processes depends on quantum tunnelling. If true, then quantum tunnelling has been central to life since its inception: life may have discovered 21st-century quantum technology billions of years ago. Quantum mechanics may be what makes life so special - the weird rules of the very small writ large in the world. If Da Vinci were alive today, he'd have tossed away any book selling dubious mysteries - instead, he'd be reading about quantum tunnelling and praying for Rooney's foot.
· Johnjoe McFadden is professor of molecular genetics at the University of Surrey and author of Quantum Evolution, published by HarperCollins
