What are enzymes in biology


Enzymes, Biocatalysts, obsolete description Ferments. Predominantly proteins (exception is e.g. catalytically active RNA, ribozymes), which are involved as catalysts in almost all chemical reactions in living organisms by reducing the activation energy required for the course of every chemical reaction. As a result, they set chemical reactions in motion under the conditions prevailing in living cells that would otherwise only take place at a noticeable rate under non-physiological conditions. Compared to the non-catalyzed reaction, the catalyzed reaction can be increased by a factor of 103-106 be accelerated. Since metabolic processes are made up of numerous individual reactions, each of which is catalyzed by a certain E. specific for each individual reaction, E. are of fundamental importance for the course of the entire cell metabolism.

Biosynthesis, structure and compartmentalization: As with all proteins, the enzyme proteins are synthesized via translation. Constantly formed E. are called constitutive E. referred to, however, are adaptive E. those that are only formed when necessary. The regulation of E. synthesis mostly takes place at the level of transcription (enzyme induction), but there are also examples of regulation at the level of translation (e.g. with certain RNA phages).

Enzyme proteins can be monomeric, i.e. consist of a polypeptide chain, or oligomeric or multimeric, i.e. consist of several polypeptide units. Monomers E. are mostly E., which are excreted by the producing cells into the extracellular space (e.g. digestive enzymes), while multimer E. are predominantly cellular E. The latter consist either of several of the same (e.g. aspartate transcarbamylase) or of different peptide subunits (ribulose-1,5-bisphosphate carboxylase / oxygenase). In addition to the protein content, many E. Apoenzyme, including non-proteinogenic groups (coenzymes, e.g. vitamins or nucleotides) that are bound to the apoenzyme either through weak interactions or temporarily, or covalently (prosthetic group). As Cofactors In addition, metals known as trace elements (including iron, copper, magnesium, manganese, zinc) appear, which serve as electron acceptors. Apoenzyme and coenzyme together make that Holoenzyme.

As Enzyme systems E.g. groups of E. are grouped together through which related, multi-stage reaction sequences are catalyzed, e.g. the enzyme system of glycolysis. However, as in the case of the fatty acid synthetase complex, they can also be present as multi-enzyme complexes due to the aggregation of several enzymes to form a larger association. Enzyme systems are usually located in certain compartments in the cell, e.g. the glycolysis enzymes in the cytoplasm, those of the citric acid cycle in the mitochondria and those of the Calvin cycle in the chloroplasts. Within the compartments a distinction can be made between enzymes that can move freely in the plasma and those that are anchored in the corresponding membranes, such as the enzymes of the respiratory chain in the mitochondrial membrane (see Fig.). However, membrane-bound enzymes can diffuse within the membrane layer to which they are bound and interact with other membrane-bound enzymes.

In different individuals of the same species, in different organs of an individual or even in the different compartments of a cell, E. occur that catalyze the same reaction, but have (mostly minor) differences in protein structure and / or kinetic properties; they are called Isoenzymes designated.

Mechanism of action: As catalysts, E. always increase the speeds of the back and forth reaction, so that under the action of enzymes only the speed at which equilibrium is established is increased, but the position of the equilibrium does not change. The chemical compound converted under the action of E. is called Substrate designated. This will be temporary during the implementation on active center of E. under training a Enzyme-substrate complex bound. The substrate and active center of an E. are complementary to one another, i.e. they fit like a key and lock, which is why each E. from the multitude of molecules occurring in the cell can bind and convert the appropriate substrate, and only this (Substrate specificity). However, two E. can also convert the same substrate, but catalyze different reactions of this substrate, so that different end products arise (Effect specificity). While the substrate specificity is mainly based on the interaction between the substrate and the active center, the interaction between the substrate and the coenzyme is also important for the effect specificity; This is particularly the case, since coenzymes themselves often undergo cyclical reactions, accompanied by the conversion of the substrate. They are therefore often also called Cosubstrate designated.