Washington: In a new study, researchers have address the question of where all the energy, which drove metabolism and replication in the first protocells, came from and why all life as we know it conserves energy in the peculiar form of ion gradients across membranes.
According to Nick Lane from UCL and Bill Martin from the University of Dusseldorf, the answer lies in the chemistry of deep-sea hydrothermal vents.
“Life is, in effect, a side-reaction of an energy-harnessing reaction. Living organisms require vast amounts of energy to go on living,” Lane said.
Humans consume more than a kilogram of oxygen every day, exhaling it as carbon dioxide. The simplest cells, growing from the reaction of hydrogen with carbon dioxide, produce about 40 times as much waste product from their respiration as organic carbon.
In all these cases, the energy derived from respiration is stored in the form of ion gradients over membranes.
This strange trait is as universal to life as the genetic code itself. Lane and Martin showed that bacteria capable of growing on no more than hydrogen and carbon dioxide are remarkably similar in the details of their carbon and energy metabolism to the far-from-equilibrium chemistry occurring in a particular type of deep-sea hydrothermal vent, known as alkaline hydrothermal vents.
Based on measured values, they calculate that natural proton gradients, acting across thin semi-conducting iron-sulphur mineral walls, could have driven the assimilation of organic carbon, giving rise to protocells within the microporous labyrinth of these vents.
They go on to demonstrate that such protocells are limited by their own permeability, which ultimately forced them to transduce natural proton gradients into biochemical sodium gradients, at no net energetic cost, using a simple Na+/H+ transporter.
Their hypothesis predicts a core set of proteins required for early energy conservation, and explains the puzzling promiscuity of respiratory proteins for both protons and sodium ions.
These considerations could also explain the deep divergence between bacteria and archaea (single celled microorganisms).
Lane says that for the first time “it is possible to trace a coherent pathway leading from no more than rocks, water and carbon dioxide to the strange bioenergetic properties of all cells living today.”