A newly discovered algal enzyme uses light to convert fats into fuel

Algae are used to make biofuel Image Source: wikimedia commons

There has always been a large interest among the scientific community to produce fuel using microbes. Scientists have successfully engineered algae that when starved for nitrogen, put most of their stored energy, into fats. These fats are chemically similar to hydrocarbons and are thus further processed into “biofuel”.

However, this processing of fats into biofuel is not a straightforward process. Most fats contain a long linear chain of hydrocarbons with one of the carbon ends linked to two oxygen atoms, making these fats slightly acidic in nature. The easiest way to process these fats into biofuel is to remove the end carbon attached to the oxygen atoms. Unfortunately, most chemical reactions are unable to specifically remove only the end carbon atoms and more commonly makes breaks randomly in the middle of the long hydrocarbon chain, and are not useful. Alternatively, other reactions require multiple steps with high input energy and low efficiency.

Fatty acid/fats have oxygen atoms at one carbon end which have to be removed to make hydrocarbons. Image Source: wikimedia commons

Interestingly, researchers from France also found the solution to the problem from microbes. Last year, they discovered that a certain species of algae converts fats directly into hydrocarbons. Now, they have identified the enzyme which is responsible for this conversion.

What is more interesting about this enzyme from the biology perspective is that it uses light for the conversion process. Essentially, this would be the fourth biological reaction that uses light for conversion apart from two reactions of photosynthesis and one for DNA repair.

After a series of biochemical tests and screening, the researchers identified the enzyme from the algal extract, the function of which was previously unknown. They identified the gene for it and engineered it into bacteria which were then observed to carry out the conversion process. They were also able to switch the conversion process on and off by switching from blue to red light- the reaction occurred in the presence of blue light.

The researchers further investigated on how the protein managed this reaction and why it requires blue light to do it. They found that the enzyme had flavin adenine dinucleotide (FAD) as a co-factor and was responsible for the absorption of blue light. On further looking into the structure of the enzyme, they found that FAD is held in close proximity to the oxygens of the fat molecule.

The authors speculate that, in the enzyme, the absorption of the blue light makes FAD to steal an electron from the fat molecule, making the fat molecule unstable. The fat then removes the carbon and two oxygens, forming carbon dioxide, to return to its stable state. After that happens, the remaining hydrocarbon steals the electron back from the FAD, resetting the enzyme for use on another fat molecule.

The discovery of this enzyme is particularly interesting, as there have been very few light-driven enzymes that have been discovered. Also, it offers an interesting premise that this enzyme can be modified to carry out different type of light-driven reactions. Finally and most importantly, this enzyme, unlike the other enzymes requires no chemical energy for the reaction, which makes the processing of chemicals a lot more easier.

Source: arstechnica