General Charateristics of Enzymes

Purpose

The purpose (actually, I should say function) of enzymes is basically to catalyze the various reactions that must occur within the body. Like a true catalyst, each enzyme is in the end itself unchanged in the reaction it catalyzes, although it may undergo several changes during the execution of the reaction. A catalyst exerts a profound effect on the rate at which the reaction takes place, often increasing it by a factor of as much as one hundred thousand to a million. In many cases this amounts to the difference between reacting and not reacting. Thus, enzymes not only catalyze reactions, they are also the means that the body uses to control which reactions occur. In order to function, an enzyme must have a precise, three-dimensional structure. By subtly (and reversibly) altering the structure of an enzyme, the body can use the enzyme as a switch to turn on and off the reaction that it catalyzes.

Naming Enzymes

Enzymes are generally named using an -ase ending. The first part of the name might be simple or complex depending on how much is known about what it does or how much is desired to be communicated.

Generally the first part of the name will include the type of reaction and/or the chemical that is reacting. For example "glutamate dehydrogenase of beef liver" tells us that this enzyme is found in liver cells of beef and that it catalyzes the dehydrogenation (or oxidation) of glutamate. This enzyme is responsible for one or more of the steps in the oxidative deamination of glutamic acid (an amino acid) to form a-ketoglutaric acid (one of the chemicals in the citric acid cycle).

This particular enzyme catalyzes part of that process. To do so it has a structure with a molecular weight of about two million. It has eight subunits each with a molecular weight of about 280,000 and those are each made of several protein chains having molecular weights of about 50,000. You can see that enzymes can be quite massive as compared to the chemicals whose reactions they are catalyzing.

Two other enzymes of which you may have heard are lysozyme and alcohol dehydrogenase.

Lysozyme catalyzes the break-down of the cell walls of bacteria, killing the bacteria. It is present in mucous and it is the first line of defense against bacterial infection. Bacteria that are present on dust particles in the air are trapped by the sticky secretions of the nasal membranes and subsequently killed by the action of lysozyme before they can multiply and cause infection.

Alcohol dehydrogenase catalyzes the first step in the metabolism of ethyl alcohol, converting it to ethanal (acetaldehyde) by an enzyme-catalyzed oxidation reaction. Ethanal, or acetaldehyde, is the compound responsible for many of the unpleasant symptoms of a hangover.

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