Enzymes are chemical substances that can be found throughout the body. They initiate chemical reactions in the body.
The word enzyme was introduced by Wilhelm Friedrich Kühne in 1878 and is derived from the Greek artificial word enzymon, which means yeast or leaven. This then found its way into international science. The international union of pure applied chemistry (IUPAC) and the international union of biochemstry (IUBMB) together developed a nomenclature of enzymes, which defines the representatives of this large group of substances as one common group. Important for determining the tasks of the individual enzymes is the naming, which classifies the enzymes according to their tasks.
The naming of the enzymes is based on three basic principles. Enzyme names ending in -ase describe several enzymes in one system. The enzyme name itself describes the reaction that the enzyme initiates (catalyzes).
The enzyme name is also a classification of the enzyme. In addition, a code system, the EC number system, has been developed in which the enzymes can be found under a numerical code of four numbers. The first number indicates the enzyme class.
Lists of all registered enzymes ensure that the specified enzyme code can be found more quickly. Although the codes are based on the properties of the reaction the enzyme catalyzes, numerical codes prove to be unwieldy in practice. More often used are systematic names designed according to the above mentioned rules.
Problems of nomenclature arise, for example, with enzymes that catalyse several reactions. Therefore, there are sometimes several names for them. Some enzymes have trivial names, which do not indicate that the substance mentioned is an enzyme. Since the names have traditionally been widely used, some of them have been retained.
Classification according to enzyme function
According to IUPAC and IUBMB, enzymes are divided into six enzyme classes according to the reaction they initiate: Some enzymes are capable of catalyzing several, sometimes very different reactions. If this is the case, they are assigned to several enzyme classes.
- Oxidoreductases Oxidoreductases initiate redox reactions.
In this chemical reaction electrons are transferred from one reactant to the other. This results in an electron release (oxidation) of one substance and an electron acceptance (reduction) by another substance. The formula for the catalyzed reaction is A??+B?A?+B?
Substance A releases an electron (?) and is oxidized, while substance B takes up this electron and is reduced. This is why redox reactions are also called reduction-oxidation reactions.
Many metabolic reactions are redox reactions. Oxygenases transfer one or more oxygen atoms to their substrate.
- Transferases Transferases transfer the functional group from one substrate to another. The functional group is a group of atoms in organic compounds that determine the properties of the substance and the reaction behavior.
Chemical compounds, which carry the same functional groups, are grouped into substance classes due to similar properties. Functional groups will be divided according to whether they are heteroatoms or not. Heteroatoms are all atoms within organic compounds that are neither carbon nor hydrogen.
Example: -OH -> hydroxyl group (alcohols)
- Hydrolases Hydrolases break down the bonds or esters, esters, peptides, glycosides, acid anhydrides or C-C bonds in reversible reactions using water. The equilibrium reaction is: A-B+H2O? A-H+B-OH.
An enzyme that belongs to the group of hydrolases is e.g. alpha galactosidase.
- Lyases Lyases, also called synthases, catalyze the cleavage of complex products from simple substrates without splitting off ATP. The reaction scheme is A-B?A+B. ATP is adenosine triphosphate and a nucleotide consisting of the triphosphate of the nucleoside adenosine (and as such a high-energy building block of the nucleic acid RNA).
However, ATP is mainly the universal form of immediately available energy in every cell and at the same time an important regulator of energy-providing processes. ATP is synthesized from other energy stores (creatine phosphate, glycogen, fatty acids) as needed. The ATP molecule consists of an adenine residue, the sugar ribose and three phosphates (?
to ?) in ester (?) or anhydride bond (?
and ? ).
- Isomerases Isomerases accelerate the chemical conversion of isomers.Isomerism is the occurrence of two or more chemical compounds with exactly the same atoms (same molecular formula) and molecular masses, but which differ in the linkage or spatial arrangement of the atoms. The corresponding compounds are called isomers.
These isomers differ in their chemical and/or physical, and often also in their biochemical properties. Isomerism occurs mainly with organic compounds, but also with (inorganic) coordination compounds. The isomerism is divided into different areas.
- Ligases Ligases catalyse the formation of substances that are chemically more complex than the substrates used, but, unlike lyases, are only enzymatically active under ATP cleavage. Energy is therefore required for the formation of these substances, which is obtained by ATP cleavage.