Unfortunately, spills happen. When large quantities of oil are accidently released from tanker ships or from off-shore drilling rigs, surfactants and other chemicals are used to clean up the contaminated areas. However, many of the chemicals used in these efforts are nearly as harmful as the oil they are designed to get rid of. Big Petroleum Corporation (BP) is developing artificial cells they will use as bioremediation agents to clear surface waters of oil in areas affected by spills. They have named these artificial life forms “Cellbots.”
The Cellbot design includes a nucleus with artificial chromosomes that contain all the genes necessary for the Cellbot to thrive and carry out its designated function. The Cellbot was also engineered to include chloroplasts and mitochondria in the cytosol so it can mimic the processes of photosynthesis and cellular respiration to make the ATP necessary to power the enzymemediated degradation of oil.
After the initial stages of Cellbot development, things were looking good. Under laboratory conditions, the Cellbots are highly effective at enzymatically degrading the oil. They are able to reproduce in range of salinities found in oceans around the world. In fact they behave in ways remarkably similar to naturally occurring cells- with one unfortunate exception. The Cellbots are able to survive and thrive only if they are provided with exogenous ATP. Even when illuminated with intense light or provided with glucose as a source of chemical energy, the amount of ATP produced by the Cellbots is insufficient to sustain them much less to power their oil-busting machinery.
As a cell biologist with expertise in metabolic processes you have been called in as a consultant to help the scientists at Big Petroleum figure out what’s wrong with their Cellbots. There are several places you could start your investigation, but you choose to look first at the process involved in metabolism of glucose to produce ATP. Your team determines that the glycolytic pathway is fine so you turn your attention to the Cellbot’s mitochondria. At the ultrastructural level the mitochondria appear perfectly normal. Biochemical assays show that all that enzymes and cofactors are present in the appropriate amounts. The electron transport chain appears to be intact. The only thing your team discovers is that the pH in the matrix of the mitochondria is the same as the pH in the intermembrane space. You report to your BP client that this is not good.
Now that you have identified a potential contributing factor to the inadequate ATP production, you set out to determine the cause of the apparent hydrogen ion equilibrium problem. You explain to the BP scientists that the electron transport chain comprises four clusters of molecules embedded in the inner mitochondrial membrane that function as redox couples.
In normal mitochondria, this results in a pH gradient across the inner membrane. Your team investigates the complexes in the electron transport chain and finds everything to be normal. Despite the normal function of the electron transport chain, the pH is the same in the matrix and intermembrane space. At a loss to explain this, one of your members suggests isolating Cellbot mitochondria and doing a complete gene expression analysis. You tell her to go ahead and when she comes back with her results, she has found something intriguing. Somehow in the design of the Cellbot mitochondria a gene for an extremely leaky hydrogen ion channel was introduced into the mitochondrial DNA and is now constitutively expressed. Closer examination reveals that this hydrogen ion channel is present as an integral membrane protein in the inner mitochondrial membrane. When presented with this new information, the BP scientists are confused.
The results of this experiment show that the hydrogen ion channel inhibitor is effective at restoring the hydrogen ion gradient in the mitochondria.