What is biocatalysis?
The human body conducts billions upon billions of chemical reactions per second with remarkable speed and efficiency.
Plants and animals do the same.
Scientists have been trying to understand and harness this ability in a laboratory setting for years through biocatalysis, the use of enzymes to perform chemical conversions of molecules in living cells.
Widely used in the pharmaceutical industry to make small molecule drugs, biocatalysis also shows tremendous promise in biotechnology and industry, fine chemicals, and food.
Incredibly, knowledge on this topic is transferable: a breakthrough in one area will lead to breakthroughs in others.
Scientists have long worked to mimic, and surpass, biological processes in the lab. It’s not hard to understand why. Most life systems are remarkably efficient: people, animals, and plants perform a staggering amount of work using very little energy.
Enzymes are particularly illustrative of this point—they waste only a scant amount of energy but give back much in return.
One of biocatalysis’s greatest uses might come in the area of energy. If scientists better understand it, they can replicate this phenomenon in such a way that it would revolutionize batteries, cars, and the composition of electricity in the national grid.
Right now, in current industrial processes, much energy is wasted. This is true even of new, more environmentally friendly sources of energy. Some industrial processes require both high pressure and high temperature, costly features that are not as optimal as what is found in living organisms.
This is what has propelled scientists for the last several decades to take a much closer look at biocatalysis as they seek to conduct chemical transformations that are as fast and efficient as what is found in living things.
But speed isn’t their only concern. The technology must also be easy to control and operate under a wide range of environmental conditions.
Significant advancement in enzyme technology and our understanding of structure–function relationships have boosted biocatalytic applications in recent decades. Despite this, biocatalysis has not yet reached its full potential.
Biocatalysis background and history
Humans have benefited from the spoils of fermentation, a particular type of catalysis, for thousands of years. One notable researcher dates the world’s oldest barley beer to 3400 B.C, the oldest grape wine to 5400 B.C., and the earliest alcohol of any kind to roughly 9,000 years ago.
Catalysis is also key to another beloved treasure: cheesemaking uses more enzymes than any other food production process.
Most cheesemaking begins with a starter culture of lactic acid bacteria and rennet, curdled milk from the stomach of an unweaned calf. The LAB, including Streptococcus, Lactococcus, and Lactobacillus, feed on milk sugars to produce lactic acid, which begins to curdle the milk and helps prevent pathogens from growing.
Diastase, a mixture of amylases, a class of enzymes that catalyze the hydrolysis of starch into sugars such as glucose and maltose, was the first enzyme to be discovered in 1833. It’s key to fermentation.
The notion of catalysts—chemicals facilitating a reaction without undergoing any change themselves—was introduced in 1836by Swedish chemist Jacob Berzelius who soon hypothesized that enzymes were, in fact, catalysts.
But his findings were not without controversy. Both the term catalysis and the phenomenon itself were heavily debated throughout the remainder of the 19th century until German chemist Wilhelm Ostwald proposed what went on to become a generally accepted definition. He said that a catalyst is a substance that accelerates the rate of a chemical reaction without being part of its final products.
French chemist and microbiologist Louis Pasteur, widely considered one of the first scientists to study biocatalysis, took this observation a step further when he contended that yeast carried out fermentation through chemical means.
After careful experimentation, Pasteur demonstrated that the end products of alcoholic fermentation are more numerous and complex than realized. Along with alcohol and carbon dioxide, there are also significant amounts of glycerin, succinic acid, and amylic alcohol. Some of these, he discovered, were optical isomers, a characteristic of many important molecules required for life.
Pasteur reproduced the process under experimental conditions, and his results showed that fermentation and yeast multiplication occur in parallel. The scientist realized fermentation is a consequence of yeast multiplication, and that the yeast must be alive for alcohol to be produced.
Years later, another critical advancement occurred. In 1905, German chemist Fritz Haber did something no one had done before. He was able to directly react nitrogen gas and hydrogen gas to create ammonia.
His process was soon scaled up by chemist and engineer Carl Bosch. Their effort is considered one of the most important technological advances of the 20th century.
Haber’s breakthrough enabled mass production of agricultural fertilizers, prompting a massive increase in crops for human consumption. He was awarded the 1918 Nobel Prize in Chemistry for his work.
It wasn’t until the 1980s that scientists turned to biocatalysis to help solve the world’s energy problems. They tried, with limited success, to use biomimicry—the design and production of materials, structures, and systems modeled on biological entities and processes—to recreate enzyme-facilitated chemical reactions in the laboratory.
But their bio-inspired catalysis didn’t work.
Enzymes have active sites where the chemical reaction takes place. The active site resides in a much larger protein scaffold, and it is not always clear what the specific role of the protein scaffold is in enzymatic function.
In early biomimicry work, scientists believed that if they could build a synthetic molecule that looked like an active site from enzymes—a structural mimic—they could replicate the chemistry that takes place via enzymes.
They soon learned that structural mimics are often not efficient catalysts. Some are not catalytic at all.
This implies that mimicking the geometry of the active site is not sufficient—one must understand other chemical properties of the active site, as well as the role of the protein scaffold.
Scientists of the 1990s and 2000s moved on to functional mimics, which do not have the same geometries of living enzymes but do have the same function. They found more success using this model.
Like other scientific fields, the field of biocatalysis exploded with the invention of the internet.
Suddenly, researchers from all over the world were able to pool their collective knowledge and drive significant advancement in the field, particularly relating to research in biomaterials used in prosthetics, biofuels, and alternative fuels.
Solar energy, fuel cells, batteries, and computer chips also have seen advancements from this research.
Developments in biocatalysis could also aid in carbon capture and in the reduction of greenhouse gases. If we knew how to capture and not release waste, we could turn it into something useful—like fuel.
Why biocatalysis is important
In addition to major gains in the creation of pharmaceuticals, advancements in biocatalysis will allow us to use energy more efficiently—and do so without the harmful environmental effects associated with burning fossil fuels.
As our world population continues to grow, our energy needs will only increase. The development of renewable energy means the creation of a reliable, diverse power supply, one that will enhance our nation’s security and reduce our reliance on foreign oil.
Biocatalysis may be key to helping meet energy demands because it can help scientists develop catalysts that can carry out key processes.
One of the biggest costs associated with sustaining human life on planet Earth is in turning nitrogen into ammonia, a key ingredient for fertilizer. Without this, we cannot grow the food we need to support a growing population.
Currently, 6 percent of the world’s energy is devoted to this endeavor. It is extraordinarily expensive—and the Haber-Bosch process we use to convert nitrogen to ammonia has not changed in 100 years.
We understand at least the basics of this process as it occurs in nature: nitrogen gas, the most abundant element in our planet’s atmosphere, diffuses into the soil from the air. Nitrogenase enzymes convert it to ammonia (N2 fixation), which can be used by plants. Scientists just haven’t figured out how they do it so well.
The mystery of biocatalysis has only been partly solved despite our close relationship with this process.
In our bodies, we have enzymes, carbon dioxide, and carbon monoxide, which are small gas molecules that can be converted into other structures. Every time we breathe, we use oxygen and produce carbon dioxide. So, our bodies know how to complete these processes, but we do not. As a result, we cannot mimic them in the lab.
Up until and including this point, biocatalysis has not been successfully used in large-scale industrial applications. There are many reasons why.
Researchers say some of the field’s greatest strengths are also its greatest weaknesses. The high specificity of enzymes means that they often catalyze commercially interesting reactions at negligible rates, or not at all, according to David J. Timson of the School of Pharmacy and Biomolecular Sciences, University of Brighton.
Their ability to work at modest temperatures and pressures means that they are often denatured if exposed to conditions outside their normal range, he wrote in a paper called “Four Challenges for Better Biocatalysts” in the journal Fermentation, published in May 2019.
In the paper, Timson argued that many enzymes are also denatured by even relatively small amounts of organic solvents. All of these issues, he said, can pose problems where enzymes are used in part of a process that includes more traditional chemical steps.
As a result, much effort has been made to alter or broaden the specificity of some enzymes. Scientists have also attempted to improve the stability of proteins so that they will be more resistant to denaturation by temperature, pressure, and organic solvents. Some of these efforts have proven successful, Timson wrote. Others, less so. Ideally, he suggested, scientists would adopt an engineering approach in which enzymes were redesigned for novel functions or expanded operating ranges.
But this requires a deep knowledge of the system being adapted. We often find that fundamental deficits in biochemical understanding limit our ability to engineer enzymes, he concluded.
The future of biocatalysis
Biocatalysis has become increasingly important across the chemical and pharmaceutical industries in recent years.
Its success can be attributed, at least in part, to a rapid expansion of the range of chemical reactions accessible, made possible by advanced tools for enzyme discovery, according to researchers out of The University of Manchester, Pfizer Worldwide Research and Development, and several other partners.
Dedicated databases and search tools have made them more accessible to a broad scientific community.
Biocatalysis has benefited, too, from advancements in molecular biology and biotechnology through the past 20 years. Tailor-made enzymes developed for particular areas of study have only strengthened scientific research in the development of pharmaceuticals.
Enzymes can be carefully crafted for practical applications with greater speed and likelihood of success than ever before, leading to greater predictability and confidence when scaling up these processes.
Scientists have already had great success in using enzymes to improve industrial chemical processing.
For example, nitrile hydratases have improved on an earlier copper-based method for converting acrylonitrile to acrylamide, the monomer used to prepare polyacrylamides. Polyacrylamides are water-soluble synthetic linear polymers with applications in pulp and paper production, agriculture, food processing, mining, and as a flocculant (a substance that makes particles clump together) in wastewater treatment.
New computational and molecular biology techniques are enabling the development of more enzymes at a faster pace. Genetic sequencing technology, for example, has led to a “gold mine” of data that can be used to assess “a huge variety of novel and mostly unexplored enzymes useful for biocatalysis,” writes Bernhard Hauer, a biochemist at the University of Stuttgart in Germany in a 2020 paper published in ACS Catalysis, “Embracing Nature’s Catalysts: A Viewpoint on the Future of Biocatalysis.”
Biocatalysis at Pacific Northwest National Laboratory
Pacific Northwest National Laboratory (PNNL) has the largest catalysis program in the United States, the Institute for Integrated Catalysis (IIC), which explores and develops the chemistry and technology of catalyzed processes. Working in conjunction with multiple other divisions within the laboratory and with universities and research partners around the world, PNNL has contributed mightily to the field through decades of fundamental research.
Recent advancements include detailed information about how catalysts help convert energy into molecular bonds, storing the energy by making bonds and releasing it by breaking bonds.
Scientists and engineers have long known that catalysts tend to slow down the longer they are in use. Researchers at PNNL, working with collaborators at Washington State University and Tsinghua University, have discovered a mechanism behind the decline of advanced copper-based catalysts.
Their findings could help improve the catalysts’ design and longevity.