Industrial enzymes

Why enzyme biotechnology is increasingly important for modern industries

Many people may be vague about the actual definition of “molecular bioscience” and what it does for the community. A prime example of biomolecules being used in our day-to-day lives – both on a domestic and an industrial scale – is enzymes.

What are enzymes?

Enzymes are biological catalysts: proteins, made in the cells, which speed up all the chemical reactions inside all living organisms. They do this by binding to substrates (chemicals involved in a metabolic reaction) and lowering the activation energy needed either to build them up into larger molecules, or to break them down into smaller ones¹.An example of an enzyme-based reaction is the breakdown of starch into glucose by amylase enzymes in the saliva.

The part of an enzyme which binds to a substrate is called its active site. The active site is very specific in structure and will only bind to a particular substrate – a bit like a key fits into a lock (in fact, this is known as the “lock-and-key” model²). Because of this, living organisms need a vast number of different enzymes – one for every chemical reaction that takes place inside the body!

Why are enzymes used so much in industry?

The use of enzymes for manufacture goes back to about 8,000 years ago³ – when humans first used yeast to ferment grapes into alcohol. In the absence of oxygen, the yeast enzymes would break down glucose into ethanol and carbon dioxide. This batch process for the production of ethanol is still used today. At the time, of course, there was no understanding of enzymes and this was merely experimental. However in modern days, as our understanding of molecular biosciences and biotechnology has improved, we have been able to exploit the properties of enzymes to use them quite diversely.

Enzyme biotechnology really took off in the 1950s. Examples of enzymes used in industrial processes include:

·         Sucrase enzymes in soft-centred chocolates

·         Proteases and lipases in baby food to start pre-digestion

·         Biological washing powders to break down stains into soluble amino acids/fatty acids

·         Pectinase in fruit juice to increase yield and make the juice clear

·         Yeast enzymes in the fermentation of sugar

·         Rennin used to coagulate cheese

·         In the textiles industry to enhance the preparation of cotton⁴

·         Esterase enzymes to remove adhesives for the recycling of paper

The list really does go on. Enzymes as a form of biotechnology are growing rapidly: Figure 1 shows the projected growth of the global industrial enzyme market up to 2015. Why are enzymes so attractive to industries?

Global industrial enzymes market, $ millions5	Estimated value in 2010	Predicted value in 2015	% increase
Technical enzymes	1000	1500	50
Food and beverage enzymes	975	1300	33

Figure 1: the global industrial enzymes market is expected to increase at a compound annual growth rate of 6%

The use of biological catalysts to speed up industrial reactions is often favoured over the use of metal catalysts for two main reasons.

Firstly, enzymes operate at fairly low temperatures and pressures, which keeps costs down. Typically the temperatures required by enzymes are about ten times lower than those required by inorganic catalysts! In addition, enzymes can be up to 10,000 times more efficient than ordinary chemical catalysts, so profit is maximised.

What are the drawbacks of enzyme biotechnology?

Figure 2: enzyme activity increases

 with temperature up until the 

optimum – then it denatures.⁶

Okay, so enzymes aren’t 100% ideal – there are drawbacks to using them. The main one is that the 3D structure of enzymes is so fragile and thus largely sensitive to changes in temperature and pH. Figure 2 shows a graph of enzyme activity against temperature. As with all chemical reactions, the rate of an enzyme-catalysed reaction increases with temperature – up to a point. The polypeptide chains in proteins are held together by weak intermolecular forces (known as van der Waals forces and hydrogen bonds). At a certain temperature – often around 42⁰C – these weak forces are overcome and the structure of the enzyme’s active site changes. This means that the substrate can no longer bind to the enzyme, which is now said to be denatured. Denaturation is an irreversible process, so industries must regulate temperature very carefully. Note from Figure 2 how the optimum temperature of an enzyme (the temperature at which it has the highest rate of activity) is just below the point where it denatures – about 37⁰C. There is a very fine balance to be struck, therefore, between increasing the rate of a reaction and not permanently denaturing the enzymes which are catalysing it.

Sharp changes in pH also cause the denaturation of enzymes because functional groups in the active sites can lose hydrogen ions in a solution which is too alkaline and gain them in a solution which is too acidic. This means that the substrate can no longer bind to the active site. Different enzymes have different optimum pHs and so this can be harder to control than temperature.

Other issues which arise are the cost of extracting enzymes and the difficulty in reusing them. Enzymes are usually extracted from micro-organisms which are grown economically in bulk fermenters⁷. However, this is not a cheap process, and because enzymes are combined with substrates in an aqueous solution it can be costly to separate and reuse them as well.

Since the 1960s⁸ industries have employed a technique which resolves all of the aforementioned problems: immobilisation. By this method, the enzymes themselves are trapped in an insoluble material such as fibrous polymer mesh, and packed into a column through which the substrate can be continually fed. There are numerous advantages to immobilising enzymes:

·         The enzymes are more stable, so they are less likely to be denatured. This also means that higher temperatures can be used, increasing the rate of reaction.

·         The enzymes can easily be recovered and reused, making immobilised enzymes a more cost-effective method.

·         The enzymes do not have to be removed from the product and do not contaminate it.

·         Since the products are separated from the enzymes, there is no “feedback inhibition” – where products bind to the active site and prevent more substrates from reacting.

However, another issue of the application of enzymes cannot be addressed by immobilisation. In the 1970s evidence arose that proteases used in biological detergents could break down keratin in the skin and lead to skin irritation⁹. Although this has not been scientifically proven many people claim to have skin sensitive to biological detergents.

Enzymes in the future?

Over time, the use and efficiency of enzymes in industry has increased rapidly and they are now used in a diverse range of industries, from textiles to tendering meat¹⁰. Of course, there is still room for development and as research continues into how the efficiency of enzymes can be improved, enzymes will be put to new uses and new ones will continue to be discovered¹⁰. A current area of research is into enzymes which can withstand greater extremes of temperature, which would be particularly desirable in laundry and industrial processes where high temperatures are needed.

Who knows what developments the future will bring; however, it can be said with reasonable certainty that the enzyme industry is one which will continue to grow and develop.

References

1.  Life Study: A Textbook of Biology by D. G. Mackean
2. A2 Level Chemistry: The Revision Guide (CGP)
3. http://www.absorblearning.com/chemistry/demo/units/LR1507.html
4. Enzyme Biotechnology in Everyday Life by Theresa Philips
5. http://www.bccresearch.com/report/enzymes-industrial-applications-bio030f.html
6. http://www.rsc.org/Education/Teachers/Resources/cfb/enzymes.htm
7. www.spolem.co.uk/worksheets/docs/industrial_enzymes.doc
8. Carrier-bound Immobilized Enzymes: Principles, Application and Design
9. New GCSE Biology by Gemma Young and Sarah Jinks
10. http://prof.dr.semih.otles.tripod.com/enzymesused/enzymesused.htm
11. 11. Semih Otles, Professor of Food Chemistry

What's new in biology? Nanoparticles allow carefully timed cancer drug delivery

A couple of months ago I wrote my first post on the topic of biomaterials, in which I touched on the use of nanoparticles in medicine. Now a recent piece of a research has caught my eye on IFLScience: http://www.iflscience.com/health-and-medicine/nanoparticles-give-tumors-one-two-punch-timing-drug-delivery

How cool is this?! Here we have two drugs which, when taken together, will attack tumour cells: erlotinib slows the growth of the cell, and doxorubicin damages the cell's DNA and prevents essential cell processes, leading to its death. The drugs have been shown to be more effective when delivered with a carefully measured time delay. And how do they discriminate between healthy cells and cancerous cells? Simple: the drugs are delivered by nanoparticles called liposomes which bind to folate receptors on cancer cells, causing the liposome to break down. The first drug is thus released into the cell, where it primes the cancer cell for the second drug, which is administered in the same way 4-24 hours later. Experiments on mice have shown that this time delay is significantly more effective than taking the two drugs at the same time.

This is a pretty big leap in cancer treatment and one of the great things is that the nanoparticles have such specificity that they can target tumour cells over healthy cells. Applications of nanotechnology are everywhere, really.

The misleading use of language

One of the banes of science is that the way we use the English language often gives rise to misconceptions about scientific facts, giving people the wrong idea about how things work. I have found that it is often the case, when studying science at school, that these ideas have to be “unlearned” and replaced with the actual science. Here are eight particularly popular examples, many of which are favourites among my own science teachers.

1.       “Close that door – you’ll let all the cold in!”

A consequence of the second law of thermodynamics is that heat naturally flows from higher temperatures to lower temperatures. So in fact, by having the door wide open when it’s below room temperature outside, you’re not letting “cold” into the house, you’re letting heat out. “Cold” isn’t a tangible thing, it’s just a lack of heat; if you were to touch a dirty surface, you wouldn’t say that you were transferring cleanliness from your hand to the surface.

2.       “You’ve got a cold? Here, have some antibiotics!”

This one is a favourite of my Biology teacher’s (is favourite the word?). The same goes for a cough. The common cold and cough are viral infections – no amount of antibiotics will cure them, because antibiotics only target bacteria.

3.       “There are an almost infinite number of stars in the universe!”

This idea of “almost infinite” being a synonym of “an extremely large number” is one that I’ve even read in Biology textbooks. In the case of the stars, no-one’s denying that there are an enormous number of stars in the universe – more than we can imagine. Well, now think about how many atoms there are in the universe. If you think too long, it’ll make your head hurt – I mean, just think of how many atoms are in a single star. Stars are made of hydrogen and helium; a single gram of hydrogen contains over 600 billion trillion atoms, whilst a gram of helium contains more than 150 billion trillion. That’s not even to mention all the atoms present in planets like our own, as well as comets and meteors. Clearly, the number of atoms in the universe is many, many orders of magnitude greater than the number of stars – but it’s no closer to being infinite! Conversely, if you believe that the universe is infinitely large, then there may well be infinitely many stars (and atoms). But there is a clear distinction: a number is either infinite, or it is not. There is no crossing bridge between the finite and the infinite; you can never reach infinity by continually adding one. Thus there can be no concept of “almost infinity”.

4.       “I’ve got a respiratory condition.”

Breathing and respiration are completely different processes and it does little to help the situation that breathing disorders are called “respiratory conditions”. Breathing is the physical process of ventilating the lungs, taking in oxygenated air and expelling deoxygenated air. Respiration, in contrast, is a biochemical pathway in which glucose is metabolised in the presence of oxygen to carbon dioxide and water, releasing energy. (There’s more to come on breathing and energy!)

5.       “Maximum luggage weight: 20kg”

This is one we are bombarded with all the time, and again it simply boils down to how we use the English language. Kilograms, stones and ounces are not units of weight – they are units of mass. Weight is the gravitational force that is pulling you towards the centre of the Earth, and is measured in Newtons. As long as you stay on Earth, your weight will remain directly proportional to your mass (one kilogram corresponds to around 9.8 Newtons). However, if you went to the moon – or even further afield – where the size of the gravitational field was different, your mass would not change, but your weight would.

6.       “Black surfaces absorb heat.”

This isn’t scientifically inaccurate, but it can lead to some confusion about cause and effect. It is not the case that, because a surface is black, it therefore absorbs heat – in fact it is more like the opposite. A surface which absorbs all wavelengths of visible light, as well as infrared (heat), will not reflect any visible light (or at least very little) and will consequently be black.

7.       “We breathe oxygen in and carbon dioxide out.”

This makes it sound like our breathing system has some sort of filter, which only lets oxygen in one way and only lets carbon dioxide out the other. When we breathe in, we create a pressure gradient that forces air – containing nitrogen, oxygen, carbon dioxide and small amounts of other gases – to enter the lungs. Oxygen then diffuses from the lungs into the blood, so that it can be used for respiration; whilst carbon dioxide, produced in respiration, passes from the blood back into the lungs. The air is then expelled from the lungs thus has a lower concentration of oxygen and a higher concentration of carbon dioxide than the air that was inhaled, but it is still a mixture of the original gases. Breathing is necessary in order to maintain a concentration gradient between the lungs and the blood.

8.       “We respire to make energy.”

This is an old one, and we’re back again to the good old laws of thermodynamics. Energy can’t be created or destroyed – it can only be transferred from one form to another!

Book review: Seven Clues to the Origin of Life by Alexander Graham Cairns-Smith

I found this book while doing research for my Extended Project, the focus of which is the RNA World hypothesis and the Miller-Urey experiment. By the time I got to the end of the book, I was convinced that neither of these were plausible explanations for the origin of terrestrial life, because Alexander Graham Cairns-Smith had utterly persuaded me that his own hypothesis was correct.

Seven Clues to the Origin of Life presents the argument that the first molecules of life were assembled on clay, which provided a template on which inorganic crystals could self-replicate. Despite the fact that there is ingenious science within the pages of the book, I found it light-hearted and enjoyable reading which was accessible for all as well as gripping. The book assumes very little prior knowledge of chemistry and biology, with the first couple of chapters introducing some fundamental principles and discussing the molecules of life. The whole thing was narrated in a detective novel style, with quotes from the original Sherlock Holmes books by Conan Doyle at the start and end of each chapter; and the intelligent use of analogies to illustrate core concepts was excellent. In particular, I liked the “scaffolding” idea, illustrating how seemingly interdependent, complex processes could have arisen from simpler building blocks, some of which were later removed. I appreciated the escape from the logic that, since nucleic acids and proteins are interdependent in today’s cells, the first organisms must have been based on RNA, as I just don’t think the random synthesis of active RNA molecules under prebiotic conditions is really plausible (again, Cairns-Smith cleverly argues this by comparing it to the probability of rolling a million 6s on a dice in a row).

The hypothesis itself was a courageous one, deviating largely from most of the current theories mainly in that it suggests that the first life forms were inorganic. Concepts such as supersaturation and self-assembly are explained with clarity and detail, while still capturing the reader’s excitement as the picture is gradually built up, describing how crystals could have formed and replicated on clay surfaces and hence acted as genes, with errors in replication leading to “evolution by direct action”.

The core theme of studying the most perplexing features of a case in order to crack it is well maintained throughout, making for enjoyable reading as well as learning. I found Seven Clues to the Origin of Life a superb book, one that should be read at the very least by anyone with an interest in the chemical origins of life, and preferably by anyone with an interest in chemistry and biology.