Enzymes

A group of compounds composed mainly of high molecular weight proteins that act as catalysts in living animal and plant organisms and are responsible for most chemical reactions. Since metabolic processes are composed of numerous individual chemical reactions, each of which is catalysed by a particular enzyme specific to each individual reaction, enzymes are of fundamental importance for the course of the entire cell metabolism. Enzymes play an essential role in the biosynthesis of specific gene products(transcription, translation). Various enzymes require metal ions (metalloproteins or metalloenzymes) as co-factors, e.g. iron (respiratory enzymes) or copper ions. Enzymes can be reversibly or irreversibly inhibited in their function by various substances (see below enzyme inhibition). On the other hand, certain processes can induce enzymes with increased enzyme synthesis.

Enzymes produced from bacteria, fungi or yeasts are used in the production of food. The enzymes themselves or their reaction products can play a role as allergens, e.g. in occupational inhalation allergies (rare).

Currently more than 2500 enzymes are known. These can be classified and named according to their occurrence in nature, their function in metabolism, their functional groups or their physical properties.

Internationally accepted is a classification based on effect specificity (EC nomenclature = acronym for "enzyme commission"). According to this classification enzymes are divided into 7 main classes:

1. E1: oxidoreductases (dehydrogenases, oxygenases, reductases). Examples are cytochrome P450 monooxidases, cyclooxygenases, glutamate dehydrogenases (GDH, GLDH)
2. E2: Transferases (transfer aldehyde, amino, glycosyl and other groups); e.g. transaminases (aminotransferases such as GOT and GPT), kinases, etc.
3. E3: Hydrolases (cleave hydrolytic ester, peptide, glycoside and other bonds); e.g. esterases, phosphatases, proteases, deaminases, etc.
4. E4: Lyases (cleave off groups (C-C, C-O, C-N) from different molecules to form double bonds (C=C) Lyases can also cause the attachment of groups to a double bond = synthases; exemplary lyases: dehydratases, decarboxylases. S.a. photolyases.
5. E5: Isomerases (catalyse the conversion of isomeric compounds; e.g. topisomerases, racemases.
6. E6: Ligases (older name: synthetases): catalyse the linking of two molecules by forming a covalent bond (C-C, C-O, C-N and others); e.g. carboxylases .
7. EC 7:-translocases (catalyse the transport of substances on or through cell membranes)

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