AN ENZYME still toiling away in modern bacteria contains signatures of the prebiotic world, suggesting that it originated in the very earliest cells. The enzyme unlocks energy from a simple molecule called pyrophosphate, and its discovery bolsters the idea that this was how primitive life first got its energy.
The universal energy currency in modern cells is a molecule called ATP. It contains a high-energy bond between two phosphate groups that supplies energy when it is broken. But ATP is a complex organic molecule, and scientists wondered how primitive cells struggling to function as life emerged could have developed such a complicated mechanism.
Almost 40 years ago, Fritz Lipmann, the scientist who first worked out the role of ATP, suggested that the original energy carrier might instead have been pyrophosphate. This molecule, found in cooling lava, consists simply of two phosphate groups joined with a high-energy bond. Some photosynthetic bacteria still use pyrophosphate as a secondary energy source. They absorb phosphate from their environment and use sunlight to create a phosphate bond, linking the molecules into pyrophosphate. Breaking the bond provides the organism with energy when and where in the cell it is needed. If this simple mechanism came first it could have paved the way for ATP.
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There was no way to test the idea. But now Herrick and Margareta Baltscheffsky, biochemists from the University of Stockholm, Sweden, have identified and analysed the sequence of the enzyme that makes and breaks that pyrophosphate bond. They found that the active sites of the enzyme, which tend to be very highly conserved throughout evolution, have unusually high concentrations of glycine, alanine, valine and aspartic acid. These are the four amino acids thought to have arisen first in the prebiotic world, suggesting that the enzyme dates from that time.
鈥淭his could be an ancient enzyme,鈥� says Herrick Baltscheffsky, adding that phosphate compounds in lava may have been important for the first life forms. 鈥淪ometimes we stumble on what appears to be a relic of the primitive age,鈥� agrees Doron Lancet, a biologist from the Weizmann Institute in Israel. 鈥淭his simple molecule could be elaborated to create ATP.鈥�
