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 word enzymon, which means yeast or sourdough. He then made his entry into international science. The International Union of Pure Applied Chemistry ( IUPAC ) and the International Union of Biochemistry ( IUBMB ) jointly developed a nomenclature of enzymes that defines the representatives of this large group of substances as a single group. Important for the determination of the tasks of the individual enzymes is the naming, which classifies the enzymes according to their tasks.
Illustration of enzymes
enzymes 6 enzyme classes:
oxidoreductases (Oxidation / reduction)
hydrolases (Use of water)
isomerases (same formula)
ligases (Addition reaction)
Enzyme / substrate complex
Enzyme / product complex
The naming of enzymes is based on three basic principles. Enzyme names that end in anase describe several enzymes in a system. The enzyme name itself describes the reaction that activates (catalyzes) the enzyme. 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 four-digit number code. The first number indicates the enzyme class. Lists of all detected enzymes ensure a faster finding of the specified enzyme code. Although the codes are based on the properties of the reaction that catalyzes the enzyme, in practice, numerical codes prove unwieldy. More frequently used are systematic names conceived according to the above-mentioned rules. Problems of nomenclature arise, for example, in enzymes that catalyze several reactions. Therefore, sometimes there are several names for them. Some enzymes have trivial names that do not indicate that the substance in question is enzymes. Since the names were traditionally widely used, they were partially retained.
Classification according to enzyme function
Enzymes are classified into six classes of enzymes according to the reaction they initiated, according to IUPAC and IUBMB:
oxidoreductases Oxidoreductases initiate redox reactions. In this chemical reaction, electrons pass from one reactant to the other. There is an electron transfer (oxidation) of the one substance and an electron uptake (reduction) by another substance. The formula for the catalyzed reaction is A ?? + B? A? + B ?. The substance A releases an electron (?) And is oxidized, while the substance B absorbs this electron and is reduced. That is why redox reactions are also called reduction-oxidation reactions. Many metabolic reactions are redox reactions. Thus, oxygenases transfer one or more oxygen atoms to their substrate.
transferases Transferases transfer the functional group from one substrate to another. As a functional group atomic groups in organic compounds are called, which determine the material properties and the reaction behavior to yellow. Chemical compounds bearing the same functional groups are grouped together because of similar properties. Functional groups will be subdivided 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 cleave 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-B-H + OH. An enzyme belonging to the group of hydrolases is eg alpha galactosidase.
lyases Lyases, also called synthases, catalyze the cleavage of complex products from simple substrates without splitting off ATP. The reaction scheme is AB? 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 nucleic acid RNA). However, ATP is primarily the universal form of instantaneous energy available in each cell and, at the same time, an important regulator of energy-providing processes. If necessary, 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 (? And?) Bonds.
isomerases Isomerases accelerate the chemical transformation of isomers. Isomerism is the appearance of two or more chemical compounds with exactly the same atoms (same empirical formulas) and molecular masses, which, however, differ in the linkage or the spatial arrangement of the atoms. The corresponding compounds are called isomers. These isomers differ in their chemical and / or physical, and often in their biochemical properties. Isomerism occurs mainly in organic compounds, but also in (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 enzymatically active only with ATP cleavage. To form these substances energy is thus required, which is obtained by the ATP cleavage.
Some enzymes are able to catalyze several, sometimes very different reactions. If this is the case, they are attributed to several classes of enzymes.
Classification according to enzyme structure
Almost all enzymes are proteins and can be classified according to the protein chain length:
monomers Enzymes that consist of only one protein chain
oligomers Enzymes that consist of several protein chains (monomers)
Multienzyme chains Several enzymes together that cooperate and regulate each other. These enzyme chains catalyze the sequential steps in the metabolism of the cell.
In addition, there are still individual protein chains that contain multiple enzyme activities, these are referred to as multifunctional enzymes.
Classification according to cofactors
Another classification is the classification according to the cofactors. Cofactors, coenzymes and cosubstrates are names for different classifications of substances that influence biochemical reactions through their interaction with enzymes. In doing so, organic molecules and also ions (mostly metal ions) are considered.
The pure protein enzymes consist exclusively of proteins and the active center is formed only of amino acid residues and the peptide backbone. Amino acids are a class of organic compounds containing at least one carboxy group (-COOH) and one amino group (-NH2).
The holoenzymes consist of a protein component, the apoenzyme, as well as a cofactor, a low-molecular molecule (no protein). Both together are important for the function of the enzyme.
coenzymes Organic molecules as cofactors are called coenzymes. If they are covalently bound to the apoenzyme, they are called prosthetic groups or cosubstrates. A prosthetic group is a protein (mostly covalently) bound non-protein components with catalytic action.
Cosubstrates are terms for different classifications of substances that influence biochemical reactions through their interaction with enzymes. As biocatalysts, molecules that accelerate reactions in organisms, the enzymes accelerate biochemical reactions. They reduce the activation energy that must be overcome in order for the substance to be converted.