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Enzyme-linked immunosorbent assays

Tests that use monoclonal antibodies to respond to a specific antigen in the blood or urine or to deliver drugs to a specific cell

Recombinant DNA technology

An alternative term for genetic engineering/genetic modification.

Monoclonal antibodies

Antibodies all made from a single clone of specialist cells used in both medical diagnostics and treatments

Neurotransmitters

Chemicals which are released in a synapse when an action potential reaches the end of one neurone. They cross the synaptic gap and trigger and impulse in the next neurone.

Digestive system

The organ system in the body which breaks down large insoluble food molecules into small soluble molecules which can be used by the body

Cell membrane

The membrane which forms the boundary between the cytoplasm of a cell and the medium surrounding it and controls the movement of substances into and out of the cell.

Bone marrow

Found in the centre of bones, it contains adult stem cells which divide and differentiate to produce red and white blood cells

Antibody

Proteins produced by the plasma cells (B cells, a type of white blood cell) of the immune system in response to a specific antigen..

Dopamine

A neurotransmitter in the brain

HIV/AIDS

Infection caused by the human immune deficiency virus (HIV). It attacks and destroys the immune system.

Diabetes mellitus

A disease resulting from a lack of insulin production by the pancreas or a loss of the cell response to insulin that causes a loss of control of the glucose balance of the body.

Antigen

The protein markers found on the surface of a cell that causes the immune system to produce antibodies against it.

Hormone

A chemical messenger produced by a particular gland or cells of the endocrine system. Hormones are transported throughout the body in the blood stream but they produce a response only in specific target cells

Fibrin

A protein produced during the clotting of the blood which traps platelets and red blood cells to form the clot

Embryo

The name for a group of cells that are developing into a fetus. In humans this is from implantation to the 8th week of development

Brain

The main organ of the central nervous system made up mainly of grey matter

Virus

The smallest of living organisms. Viruses are made up of a ball of protein that contains a small amount of the virus DNA. They can only reproduce after they have infected a host cell

Urine

The liquid which leaves your body through the urethra. It contains water, salts urea and other chemicals.

Human chorionic gonadotrophin (hCG)

Hormone made by the early embryo as it implants in the uterus and used in pregnancy tests to indicate pregnancy

Enzymes in medicine

Enzymes are widely used in medicine, from the biotechnology used to make specific drugs to diagnostic tests and treatments.

Examples of common medical uses of enzymes include:

1. Dip-sticks used for testing urine

These relatively simple tests indicate the presence or absence of a range of different chemicals that in turn indicate infections, problems in the kidneys or other problems such as diabetes that can result in glucose in the urine.

Example: Glucose oxidase is the enzyme found on dip-sticks used for testing urine for glucose

The enzyme is mixed with peroxidase and a blue dye. If the urine contains no glucose then the dye stays blue. However, if there is glucose present, the enzyme breaks up the glucose and releases hydrogen peroxide. This in turn reacts with the other chemicals, turning the dye from blue to green to brown depending on the glucose levels.

Uristicks

Enzyme technology enables doctors to see that the only abnormality in the urine of this patient is the presence of glucose

2. Enzyme-linked immunosorbent assays (ELISAs)

These tests are also widely used to detect antibodies to particular infections. ELISAs use monoclonal antibodies to respond to a specific antigen in the blood or urine. Enzymes are used to deliver a colour change if the test is positive.

ELISAs are also used in testing for allergens at very low concentrations, and for the diagnosis of a range of infectious diseases including HIV/AIDS, West Nile virus and Newcastle Disease. They are also used for diagnosing a range of plant diseases and diseases in wild and domestic animals.

Example: ELISA used in pregnancy testing

As a human embryo begins to implant in the uterus and develop it produces a chemical called Human Chorionic Gonadotrophin (hCG). Some of this hormone is found in the blood and the urine of the mother. Modern pregnancy tests rely on monoclonal antibodies to test for hGC in the urine. Some pregnancy tests are so sensitive that pregnancy can be detected within hours of implantation. Often a pregnancy test is carried out first thing in the morning, when the levels of hGC are highest. A pregnancy test contains mobile monoclonal antibodies for hGC that have enzymes attached to them. They will only bind to hCG. If the woman is pregnant the hCG in her urine binds to the mobile monoclonal antibodies and forms an hCG/antibody complex (complete with enzymes). These complexes bind to immobilised antibodies arranged in a line or a pattern such as a positive (+) sign when the enzymes catalyse a reaction to produce a coloured mark. If the woman is pregnant, a coloured line or pattern appears in the first window.

The urine then continues up through the test to a second window. Here there is usually a line of immobilised monoclonal antibodies that bind only to the mobile antibodies, regardless of whether they are bound to hCG or not. Again when the mobile antibodies bind it triggers an enzyme reaction that results in a coloured line. This coloured line forms regardless of whether the woman is pregnant – it simply indicates that the test is working.

If the woman is pregnant, two coloured patterns appear. If she is not pregnant, only one appears.

Enzyme pregnancy test diagnosis

Using enzymes to help diagnose pregnancy – it is the action of enzymes that causes the formation of the coloured lines that indicate pregnancy

Positive pregnancy test

A positive pregnancy test (Klaus Hoffmeier, public domain)

3.Enzyme replacement therapy

In some disease, the body cannot make specific enzymes. The lack of these enzymes can cause severe symptoms of disease and even in some cases death. For example, Gaucher’s disease is a genetic disease where the body does not make the enzyme glucocerebrosidase. This enzyme breaks down glucosyceramide, a component of the cell membrane in the removal of cells that are worn out or damaged in some way. As a result there is a build-up of glucosyceramide in organs including the spleen, liver, lungs, brain and bone marrow. It causes an enlarged liver and spleen and many metabolic problems. Children who inherit the most severe form of the disease often do not live beyond the age of two.

The most common form of Gaucher’s disease affects about one in every 40,000 live births in the US. In recent years new drugs such as velaglucerase alfa have been developed. They are produced using recombinant DNA technology (genetic engineering) of bacteria. The drugs are expensive and an affected person has to take the drug for life, but it effectively replaces the missing enzyme and allows them to live a normal life.

Microphages

Macrophages in bone marrow affected by Gaucher’s disease (Nepron, CC BY-SA 3.0)

4. Prodrug therapy

Some medicines are delivered to the body in an inactive form. They only become active when they are acted on by enzymes in the body. This happens in much the same way as trypsin is produced as trypsinogen in the body, and fibrinogen is the precursor of fibrin in the blood clotting cascade. Some prodrugs are activated by the enzymes of the digestive system. Others are only activated when they are actually inside the body cells.

Lisdexamfetamine is a drug that can be used to help children who are affected by ADHD – attention deficit hyperactivity disorder. It has an effect on the areas of the brain associated with self-control and attention so they function better. Lisdexamfetamine is a prodrug – it is inactive. In the body it is converted to dextroamphetamine by enzymes that remove a lysine (amino acid) group. The active drug acts on neurotransmitters including serotonin, dopamine and noradrenaline in the synapses of the brain (see Cell Biology, Page 9). This drug is closely linked to the illegal recreational drugs known as amphetamines.

Chemical structure of Lixdesamfetamine

The chemical structure of lisdexamfetamine (JaGa, CC BY-SA 3.0)