The way enzymes work can also be shown by considering the energy changes that take place during a reaction. Consider a reaction where the product has a lower energy than the substrate, so that the substrate naturally turns into product the substrate must overcome the Activation Energy. The larger the activation energy, the slower the reaction will be because only a few substrate molecules will have enough energy to overcome the activation energy barrier. Most physiological reactions have large activation energies, so they simply don’t happen on useful time scale. Enzymes reduce the activation energy of a reaction, so that most molecules can easily get over the activation energy barrier and quickly turn into product.
The rate at which enzyme reactions happen is dependent on different factors which affects the enzyme reaction. The most important are the pH level, the temperature at which the reaction occurs, and the amount of substrate compared with the amount of enzyme present.
Enzymes have a maximum pH level, which they will work fastest. For the majority of enzymes it is approximately pH 7-8, however a few enzymes can work at very high pH, such as protease enzymes in animal stomachs, which have a maximum of pH 1. The pH affects the charge of the amino acids at the active site. The properties of the active site change and the substrate can no longer bind.
The effect of temperature is similar to that of pH, in that there is a maximum temperature that they work fastest. In mammalian enzymes this is about 40 degrees. Adding heat to the reaction the rate increases because the enzyme and substrate molecules both have more kinetic energy so collide more often, and also more molecules have enough energy to overcome the activation energy. If there is no heat the rate of the reaction is not zero, but they work slowly. Above the maximum temperature the rate of reaction decreases as more and more enzyme molecules Denature. The thermal energy breaks the hydrogen bonds holding the structure of the enzyme together. The enzyme especially the active site loses its shape and the substrate can no longer bind, and the reaction is no longer catalysed. At very high temperatures this is irreversible
If the concentration of enzyme increases, the rate of reaction increases. This is because there are more enzyme molecules available to catalyse the reaction. At very high enzyme concentration the substrate concentration may become rate limiting, so that the rate of reaction stops increasing.
As the substrate concentration increases the rate or reaction increases. This is because more substrate molecules can collide with enzyme molecules, so more reactions will take place. At higher concentrations the enzyme molecules become saturated with substrate and there are few free enzyme molecules.
It is essential for some enzymes to have a Cofactor; this is a non-protein substance to function efficiently. The three types of cofactor are, Activators these are necessary to the efficient function of the enzyme Thrombokinase that converts prothrombin to thrombin during blood clotting, and it needs calcium to activate the reaction. Just like the presence of chloride is required for Salivary Amylase to convert starch into maltase.
The activators assist in the enzyme by moulding the enzyme or substrate molecule into a more suitable shape.
Coenzymes, a non-protein organic substance, which are not bound to the enzyme. Derive from vitamins, Nicotinamide adedinie dinucleotide (NAD) a member of the vitamin b complex. This acts as a coenzyme by acting as a hydrogen acceptor to dehydrogenases. Then there are the Prosthetic Groups, like coenzymes they are organic, but unlike coenzymes they are bound to the enzyme. The best-known group is Haem. These are ring shaped molecules with iron in its centre, which carry oxygen in the haemoglobin, but also it is the prosthetic group of the electron carrier cytocrhome and the enzyme catalase.
Inhibitors as their name suggests inhibit the activity of enzymes, reducing the rate of there reactions. They’re naturally there, but are also used artificially as drugs and pesticides. There are two kinds of inhibitors. The first being a Competitive Inhibitor. The structure of this molecule is similar to the substrate molecules, it to can fit into the active site. It therefore competes for the active site, so the reaction is slower. If the concentration of substrate is greater than the concentration of inhibitors then the inhibition will be less.
A Non Competitive inhibitor molecule is different in structure to the substrate and does not fit the active site. The inhibitor molecule occupies its own site somewhere else on the enzyme. Therefore all the inhibitor molecules can have an effect, when the inhibitor is in place the active site for the substrate is changed, so the enzyme is inactive. When the inhibitor leaves, the enzyme is then activated.
Enzymes are not only found in the body, they are also found in medical and commercial use. A wide range of sources are used for commercial enzyme from spinach to snake venom. Of the hundred or so enzymes being used industrially, over a half are from fungi and yeast and over a third are from bacteria. A much larger number of enzymes are used in chemical analysis and clinical diagnosis. Non-microbial sources provide a larger proportion of these, at the present time. Microbes are preferred to plants and animals as sources of enzymes because, they’re cheaper to produce, also plant and animal tissues contain more potentially harmful materials than microbes, including phenolic compounds (from plants), endogenous enzyme inhibitors and proteases.
Here are a few important commercial enzymes and their sources.
As the tables show there are many different uses for enzyme from food to brewing
and pharmaceutical to medicine. We will now look at two commercial uses and two uses in medicine.
Enzymes have been utilised in the laundry and detergent industry since the mid 1960’s. (Which apart from the brewing industry they are probably the best-known application of enzymes in industry.) With examples of biological washing powders, liquids and tablets.
The most used enzyme in bio-powders is Protease this acts on organic stains like grass, sweat and blood. In recent years a mixture of enzymes like Lipase and Amylase have been included for effective results on stains like oils and fats and starchy food deposits. Now we have powders for colour enhancing and anti bobbling,
which contain Cellulase. The cellulase removes detached cellulose fibrils, which dull the colour because dirt is trapped on the rough surface of the fabric.
Enzymes are becoming important to the development of spot application to laundry in which the dirt is loosened by the enzyme before they go into the main wash in a detergent. These products reduce the energy and temperature of the wash therefore work out cheaper for the consumer
It has also become more popular to use enzymes in dishwasher detergents such as protease and amylase to remove stubbin food particles.
Human beings have been producing beer for thousands of years; beer brewing involves the production of alcohol with the use of yeast on various plant materials like barley, maize, hops and rice. Yeast is a fungus whose enzymes catalyse the breakdown of sugar (glucose) into alcohol (ethanol) and carbon dioxide. The majority of the sugars in plant materials are Complex Polysaccharides like starch and can’t be easily used. These nutrients are released by malting, where the barley is allowed to partially germinate, this allows Endogenous enzymes to be released and degrade starch and protein to simple sugar’s and amino acids that the yeast cells can use. This process is an expensive and hard to control method of manufacturing enzymes, so industrial enzymes like Amylase, Glucanase and Protease are added to unmalted barley resulting in the same sugars and amino acids but more controlled
This process is used for all alcoholic beverages, but stronger beverages like whisky and vodka have to be distilled afterwards to increase the concentration of ethanol in the fermented mixture. The reason for this is because the ethanol poisons the yeast and stops it working when its concentration builds up to 18% by volume.
Enzymes play a role in filtration improvers. Pre- treating the mash or final beer with Xylanase or Glucanase to break down polysaccharides like Xylans and Glucans increases filtration rates and prevents fouling of filtration membranes.
Enzymes play an important role in the detection of diabetes, pregnancies, drugs in urine and the detection of HIV using the technique Enzyme Linked Immunosorbant Assay (ELISA). This works by immobilising the antibodies and passing the test solution over them. If we were looking for a certain chemical, and it was present in the solution it will attach to the antibodies, an antibody with an enzyme attached is added. It only reacts with the original antibodies, which are linked to the certain chemical. A substrate is then added which the enzyme causes a change in colour. The amount of the chemical we are looking for is shown by the amount of colour change in the substrate. They come in different forms from urine dipsticks for home pregnancy kits, blood glucose test strips for diabetes and the aids test.
Enzymes are used for patients with enzyme deficiencies. An example is in the treatment of haemophilia by administering blood clotting factors or the use of protease to degrade fibrin. The use of protease prevents the formation of dangerous blood clots. The protease used in the therapy of thromboembolic diseases myocardial infarction (TDMI) and deep venous thrombosis is called tissue plasminogen activator.
In this assignment we have looked at the biological structure and function of enzymes in the human body and described some of their industrial and medical uses and their source’s. It shows the importance to chemical reactions in and out of the body, it also shows exactly what the enzymes need to work quickly and efficiently and what factors contribute to this, and also what factors prevent and disrupt enzyme reactions.
Barry Hollinshead, H.E.F.C.
Human Biology.
Word count 2109
