Enzymes catalyze different reactions in the body.

Enzymes are chemical substances that can be found all over the body. They set chemical reactions in motion in the body.


The word enzyme was made by Wilhelm Friedrich Kühne 1878 and is derived from the Greek made-up word enzymon, which means yeast or sourdough. This then found its way into international science. The international union of pure applied chemistry (IUPAC) and the international union of biochemstry (IUBMB) worked together to develop a nomenclature for the enzymes that defines the representatives of this large group of substances as a common group. The naming, which classifies the enzymes according to their tasks, is important for determining the tasks of the individual enzymes.

Illustration of enzymes

Figure Enzymes: Classification and substrate specificity of enzymes

6 enzyme classes:

  1. Oxidoreductases
    (Oxidation / reduction)
  2. Transferases
  3. Hydrolases
    (Use of water)
  4. Lyases
  5. Isomerases
    (same empirical formula)
  6. Ligases
    (Addition reactions)
  7. Substrates
  8. Active center
  9. Enzyme / substrate
  10. Enzyme / product

An overview of allhe images by Dr-Gumpert can be found at: medical illustrations


The Naming the enzyme is on three basic principles based. Enzyme names ending in –ase describe several enzymes in a system. The enzyme name itself describes the reaction that the enzyme sets in motion (catalyzed). The enzyme name is also a classification of the enzyme. In addition, a code system that EC number system, in which the enzymes are made under a numerical code four numbers can be found. The first number indicates the enzyme class. Lists of all detected enzymes ensure that the specified enzyme code can be found more quickly. Although the codes are based on the properties of the reaction that the enzyme catalyzes, in practice numerical codes prove to be unwieldy. Systematic names based on the above rules are used more frequently. Problems with the nomenclature arise, for example, with enzymes that catalyze several reactions. Therefore, there are sometimes several names for them. Some enzymes have trivial names that 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:

  • Oxidoreductases
    Oxidoreductases set redox reactions in motion. In this chemical reaction, electrons are transferred from one reaction partner to the other. One substance releases electrons (oxidation) and another substance accepts electrons (reduction).
    The formula for the catalyzed reaction is A ?? + B? A? + B ?.
    Substance A releases an electron (?) And is oxidized, while substance B absorbs 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. Functional groups are atomic groups in organic compounds that determine the substance properties and the reaction behavior to a large extent. Chemical compounds that have the same functional groups are grouped into substance classes due to their similar properties. Functional groups will be divided according to whether or not they are heteroatoms. Heteroatoms are all atoms within organic compounds that are neither carbon nor hydrogen.
    E.g .: -OH -> hydroxyl group (alcohols)
  • Hydrolases
    Hydrolases split the bonds in reversible reactions using water. Esters, esters, peptides, glycosides, acid anhydrides or C-C bonds. 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 an energy-rich 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-supplying processes. If required, ATP is resynthesized from other energy stores (creatine phosphate, glycogen, fatty acids). The ATP molecule consists of an adenine residue, the sugar ribose and three phosphates (? To?) In ester (?) Or anhydride bonds (? 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 empirical formula) and molecular weights, which, however, differ in the connection or the spatial arrangement of the atoms. The corresponding compounds are called isomers.
    These isomers differ in their chemical or / and physical, and often also in their biochemical properties. Isomerism occurs primarily with organic compounds, but also with (inorganic) coordination compounds. The isomerism is divided into different areas.
  • Ligases
    Ligases catalyze the formation of substances that are chemically more complex than the substrates used, but, in contrast to the lyases, are only enzymatically effective with ATP cleavage. The formation of these substances therefore requires energy, which is obtained through the splitting of ATP.

Some enzymes are able to catalyze several, sometimes very different, reactions. If this is the case, they are assigned to several enzyme classes.

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  • Alpha-glucosidase
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  • Trypsin

Classification according to enzyme structure

Almost all enzymes are proteins and can be classified according to the length of the protein chain:

  • Monomers
    Enzymes that consist of only one protein chain
  • Oligomers
    Enzymes that consist of several protein chains (monomers)
  • Multi-enzyme chains
    Several aggregated enzymes that cooperate and regulate each other. These enzyme chains catalyze the successive steps in the cell's metabolism.

In addition, there are individual protein chains that contain several enzyme activities; these are referred to as multifunctional enzymes.

Classification according to cofactors

Another classification is the classification according to the consideration of the cofactors. Cofactors, coenzymes and co-substrates are names for various classifications of substances that influence biochemical reactions through their interaction with enzymes.
Organic molecules and ions (mostly metal ions) are considered.

The pure protein enzymes consist exclusively of proteins and the active center is only formed from amino acid residues and the peptide backbone. Amino acids are a class of organic compounds with at least one carboxy group (-COOH) and one amino group (-NH2).

The holoenzymes consist of a protein component, the apoenzyme, and a cofactor, a low molecular weight molecule (not a protein). Both together are important for the function of the enzyme.

Organic molecules as cofactors are called coenzymes. If they are covalently bound to the apoenzyme, they are called prosthetic groups or co-substrates. A prosthetic group refers to non-protein components firmly (mostly covalently) bound to a protein with a catalytic effect.

Cosubstrates are names for various classifications of substances that influence biochemical reactions through their interaction with enzymes. As biocatalysts, molecules accelerate reactions in organisms, enzymes accelerate biochemical reactions. They reduce the activation energy that has to be overcome so that the substance can be converted.