8. Enzymes as tools

‘Enzymes as tools’ addresses the application of enzymes on the industrial stage. In the past, there were considerable barriers to this wider application of enzymes: enzymes were typically fragile and unsuitable for robust industrial handling. By using genetic methods and unusual organisms enzymologists today are able to obtain sturdy enzymes in amounts that make them economically realistic for industrial use, and supplying these enzymes is the central business of a number of large companies. One of the largest markets for enzymes is as additives in washing powders for clothes and in tablets for dishwashers. Other areas of application for enzymes include food production, hair removal, farming and waste treatment, and industrial chemistry.

6. Metabolic pathways and enzyme evolution

‘Metabolic pathways and enzyme evolution’ focuses on metabolic pathways and enzyme evolution. Although a few enzymes catalyse a single isolated reaction, most are part of a team that catalyses a series of reactions in which each enzyme picks up its predecessor’s product, taking it a step further to create a metabolic pathway. This pathway may be to build up, say, an amino acid from simpler starting molecules, or conversely to break down food molecules to yield new chemical building blocks and sometimes also to trap useable energy. Life is the combined outcome of this seemingly logical enzyme teamwork.

4. Structure for catalysis

‘Structure for catalysis’ details the various patterns of enzyme mechanism and the various structural features helping to achieve catalysis. One of the striking features of enzyme catalysis is substrate specificity. In the lock-and-key hypothesis, the enzyme is viewed as a precisely shaped lock and only the right key, the substrate, can fit and turn it. The lock-and-key combination is the enzyme–substrate complex. A crucial ingredient of the enzyme’s equipment for achieving outstanding catalysis is the ‘catalytic groups’.

7. Enzymes and disease

‘Enzymes and disease’ assesses how, in relation to medical science, enzymes may be the problem or they might offer the solution. What happens if enzymes are faulty in some way? Enzyme defects lead to diseases such as alkaptonuria, phenylketonuria, Sudden Infant Death Syndrome (SIDS), and Jamaican Vomiting Sickness. On the other hand, there are often situations in which humans deliberately seek to damp down the activity of normally functioning enzymes in human bodies, and this is how many drugs work. Enzymes, human or otherwise, are also nowadays widely used as agents for diagnosis or therapy.

9. Enzymes and genes—new horizons

‘Enzymes and genes—new horizons’ studies molecular genetics. It details how the method of ‘site-directed mutagenesis’ opened the door to what rapidly became known as protein engineering. Initially, people wondered whether mutated proteins would fold up properly. Occasionally they did not, but, overall, protein engineering has been remarkably successful and has become a powerful tool for pure research, allowing one to test the contribution of different parts of a protein structure with surgical precision. Amino acid dehydrogenases are a family of enzymes. There have been three breakthrough discoveries in modern molecular genetics that rely on remarkable enzymes. These discoveries have transformed biotechnology, biology, and people’s lives.

5. Enzymes in action

‘Enzymes in action’ explores a few interesting examples which illustrate the sophistication and subtlety of enzymes in action. One function of the digestive system is to dismantle food proteins, releasing the amino acids for one’s own use. For this, there is a set of enzymes called proteinases. The zymogen is an inactive enzyme precursor that is only ‘switched on’ at the appropriate time so that the potent protein degrading activity appears when, and only when, the food is there to keep it fully occupied in gainful activity.

3. The chemical nature of enzymes

‘The chemical nature of enzymes’ evaluates the chemical nature of enzymes. To discover the chemical nature of enzymes, it was essential to obtain them in a pure form. To this end, the early biochemists devised various procedures, including fractionation and column chromatography. However, purification of enzymes led to controversy, which ultimately revealed that enzymes are proteins. Proteins are biological polymers, that is, they are built of similar units joined end to end to form very large molecules. Chemically, a protein molecule is a linear polypeptide.

2. Making things happen—catalysis

‘Making things happen—catalysis’ examines chemical catalysis, considering what makes a reaction go or not go and how enzymes catalyse particular chemical reactions. This process is not unique to living systems, although enzymes are both more potent and more selective than catalysts encountered elsewhere in chemistry. A catalyst is an agent that speeds up a chemical reaction but remains unchanged itself at the end of the process. Since a catalyst is not altered or used up, it can be used over and over again.

1. No enzymes, no life

‘No enzymes, no life’ discusses the role of enzymes and how they orchestrate the whole of life. Almost every chemical step in every living thing is guided by its own dedicated enzyme. Out of all the multitude of reactions that might theoretically be possible, enzymes select and guide the orderly sequences of reactions which are called ‘metabolism’, breaking down foodstuffs stepwise to give useful building blocks and reassembling them to make new biological molecules. Ultimately, enzymes control every biological process. Can chemistry explain biology?