by Emily Benton
‘Tis the season to be jolly…. and on the road driving to family and friends for the holiday, spending an obscene amount of money on gas. “I remember when gas was five cents a gallon,” says Grandpa Joe. Well, what if there was a way to make gas cheaper, environmentally friendly, and less toxic? We will probably never see the price of gas at five cents a gallon again, but it would be nice if we didn’t have to pay the almost-four-dollar prices we’re seeing today. Studies have found that by reversing a simple reaction may have the potential of efficiently providing the resources for producing fuel. We all know what that means—more efficient means less money!
The production of fuels (and other chemicals) that consists of long, linear chains of carbon and hydrogens (a.k.a fatty acids) involves several condensation reactions, making carbon-to-carbon bonds. One example of this type of condensation reaction is what has been referred to as reverse β-oxidation. Regular β-oxidation is a series of reactions that degrade a long, fatty acid chain into several smaller two-carbon molecules of acetyl-CoA; therefore, reverse β-oxidation is the opposite of that, making long-chain alcohols and fatty acids (Nelson et al.2005) (Figure 1).
Unlike regular β-oxidation, reverse β-oxidation must be able to operate on sources other than fatty-acids. The pathway of reverse β-oxidation utilizes acetyl-CoA, other coenzyme A- containing molecules, and a set of what are known as termination enzymes that includes thiolases (transfer acetyl-CoA), dehydrogenases (transfer a hydride, :H-), reductases (add electrons, such as the case of forming a bond) and thioestersaes (make alcohols and acids from an ester). As discovered in the study of Dellomonaco and other researchers, certain genes in Escherichia coli that code for these termination enzymes must be triggered in order for them to be expressed. This reaction takes place when generating even-chains. When producing odd-chains, which are less often seen in nature, a three-carbon molecule containing coenzyme A is used instead of acetyl-CoA. Other condensation reactions require the activation of malonyl-CoA, which requires energy, while reverse β-oxidation does not, making it much more efficient (Dellomonaco et al. 2011).
One of the significances of reverse β-oxidation is its ability to regenerate the chemicals that are needed for producing fuel. An increasingly popular alternative fuel is biodiesel, which is produced from vegetable oils (a fatty acid) and alcohol, such as methanol. When fatty acid and methanol react, a fatty acid methyl ester (FAME) forms, which is essentially fuel. However, often times the vegetable oils are already used (cooking oil) and need to be purified before producing FAME. It is also sometimes difficult to obtain enough used oil. Therefore, if reverse β-oxidation ends up being cost efficient when producing mass amounts of fatty acids, these fatty acids can be used for producing FAME (Diesel Fuel).
The use of biodiesel fuel over petroleum has many benefits. First of all, it is biodegradable and nontoxic, making it environmentally friendly. For instance, biodiesel fuel has a significantly lower amount of sulfur. The adverse affects of sulfur is that it forms sulfur oxides and sulfates that can make acid rain, which has been found to be very corrosive. Secondly, the use of biodiesel lowers carbon monoxide (CO) emissions by 50% and lowers emissions of particulate matter by 30%. Also, using biodiesel instead of petroleum has recently been found to reduce the amount of carcinogens in the atmosphere by an average of 75%, which is a lower health risk for people (Diesel Fuel). Biodiesel fuel is also more economical due to the increasing prices of crude oil and limited supply of fossil fuels (Ma et al. 1999).
Alternative fuels are necessary, especially with the economy the way it is today. Several studies have discovered new ways of producing these alternative fuels, but one problem that still arises is energy cost. This study has been able to reverse the naturally occurring process of β-oxidation that condenses small organic molecules into long chains that may result in less expensive fuel one day.
- Dellomonaco, C., Clomburg, J.M., Miller, E.N., and Gonzalez, R. (2011) Engineering Reversal of the β-Oxidation Cycle for the Synthesis of Fuels and Chemicals. Nature 476: 355
- Diesel Fuel (Internet). Wikipedia, the Free Encyclopedia. 2011 Nov 5. (cited 2011 Dec 6).
- Ma, F. and Hanna, M.A. (1999) Biodiesel Production: A Review. Bioresour. Technol. 70: 1-15
- Nelson, D.L. and Cox, M.M. (2005). Lehninger Principles of Biochemistry, 4th Edition. New York: W. H. Freeman and Company: 648-649