New routes to driving enzyme-catalysed chemical synthesis using hydrogen gas

Bacterial cells act as miniature chemical factories and have evolved specialised routes to making many of the sorts of molecules that we use as pharmaceuticals, pleasant fragrances, food additives or chemicals for use in agriculture. The key parts of the cells for carrying out this work are the enzymes. It is possible to break cells open and isolate an enzyme for making a specific molecule. Bacteria can also be engineered to make artificial chemicals, expanding the range of molecules they can produce. Procedures are now well-established for growing bacteria on a large scale and isolating large quantities of enzymes, and at the same time, chemical companies are starting to realise the benefits of using enzymes instead of traditional chemical routes. In the production of complicated molecules such as drugs, fragrances and food flavourings, enzymes generate much less waste, make purer chemical products, and allow chemistry to be carried out in water rather than toxic, polluting solvents. The purity of the end product is particularly important in the food and pharmaceutical industries where contaminants may have serious, harmful effects.

Although there has been increasing interest in using enzyme catalysis in chemical production, many challenges remain to be overcome before this approach can be widely adopted. Once isolated from their cells, enzymes are often quite unstable. Their stability can be improved by attaching them to surfaces, but this often requires complicated attachment processes and can be expensive. Secondly, many enzymes only work in the presence of special helper-molecules called cofactors which are used up by the enzymes in the process of making chemicals. The cofactors are also expensive, and for enzyme processes to be economically viable, it is essential to have some way of recycling the cofactors. Unfortunately, the currently-available methods for recycling the cofactors make even more waste which contaminates the desired chemical products. We have developed a technology that addresses both of these challenges, offering a much-needed step change for enzyme catalysis. At the moment, our technology has only been demonstrated on a small scale in our laboratories, but we now need to convince the chemical, pharmaceutical and food industries that this offers real benefits for the future of chemical production.

Our technology works as follows: once we have isolated enzymes from the bacterial cells, we immediately attach them onto cheap carbon beads. This is a very simple one-step process. We attach several different types of enzyme to each bead so that the enzymes can work together to carry out each step in making chemicals. We supply the beads with low, safe levels of hydrogen gas, and this provides the energy for recycling the cofactors and to drive the enzyme machinery necessary to make the required chemicals. To make a desired chemical, we start by putting a cheap chemical building-block in water, we bubble in a little hydrogen gas, add our enzyme-modified beads, and after a few hours, the desired chemical product is ready to collect! The enzyme-modified beads can be easily scooped out of the reaction mixture, leaving nothing else except the desired product and a tiny trace of the harmless cofactor. As an added bonus, the beads can be collected and re-used a number of times, minimising the cost of using enzymes.

To take our concept from a lab-scale idea to a technology ready for industry to adopt, we need to show that we can produce the enzymes on a large scale. We need to show how quickly the beads can produce chemicals, and how pure the products are. This project will answer these sort of questions, so that at the end of the 5 years, we can convince potential customers (chemical, pharmaceutical and food additive companies) that our technology will allow them to make chemicals more cheaply and in a more environmentally-friendly way.

As described in proposal submitted to IUK