A enzyme (female name, sometimes used with the masculine) is a Molécule (Protéine or ARN in the case of the Ribozyme S) making it possible to accelerate until million times the chemical reactions of the Métabolisme being held in the cellular medium or extracellular. The enzymes act with weak concentration and they are found intact at the end of the reaction: they are biological Catalyseur S (or biocatalysts). The first enzyme was discovered by Anselme Payen and Jean-François Persoz in 1833. After having treated an aqueous extract of Malt with the ethanol, they precipitated a substance sensitive to heat. This substance was able to hydrolize the Amidon: they named it diastase (ethym: diastasis=separation) because it separated the soluble Sucre from the starch.
The first isolated enzymes were initially named Ferment S and thereafter diastases .
There exist two main categories of enzymes: the purely proteinic enzymes (which are made up only of Amino-acid) and the enzymes which are in two “parts”:
- a proteinic part: “the Apoenzyme”;
- a not-proteinic part: “the cofactor”;
- the association of the proteinic part (apoenzyme) and the not-proteinic part (cofactor) constitutes “the Holoenzyme”.
Example: AminoAcyl transférase (enzyme fixing the amino-acid on the ARN transfer) needs ATP (Coenzyme) to fix the amino-acid on ARNt.
The active site or role
See also: active Site
The function of the enzymes is related to the presence in their structure of a particular site called the active Site which with the shape of a cavity or a furrow in which the transformation of the substrates into product takes place.
The enzymatic activityThe reaction speed enzymatic is measured starting from the quantity of formed product or reagent disappeared per unit from time. The affinity of the enzyme for its substrate is given by its km or Constante of Michaelis in the case of a simple enzyme, with only one site of fixing (enzyme known as michaélienne ). This one is defined as the concentration of substrate for which the reaction speed enzymatic is half the reaction speed maximum.
Many factors can modify the reaction speed enzymatic:
- concentrations in enzyme and substrate
- concentrations in metal ions
- physicochemical characteristics of the medium of reaction (temperature, pH,…)
- the presence of inhibiting S of the enzymatic reaction
The enzymatic reaction depends on several factors:
- the temperature: in optimal conditions, it must approach the 37/38°C. These values are indicative enzymes of warm-blooded animals, that is to say almost the temperature of the body. Contrary, if the temperature exceeds the 60°C, the enzyme is denatured (rupture of the hydrogen bonds located in variable parts of protein), there is modification of the active site, and the reaction cannot take place. If the temperature is in lower part of 5°C, the enzyme is inactivated. There exist thermostable enzymes, such as for example the DNA polymerase used in PCR.
- pH: according to the reactions, complex i/o will have to be done with neutral pH, as for the Hydrolyze of the starch, with acid pH, approximately 3, for pepsin for example, or to basic pH, 8 for trypsin. The state of protonation either of the active site or of the site of connection can indeed be critical in the activity of the enzyme. Contrary, certain enzymes are relatively not very sensitive to the variations of pH.
Regulation of the enzymatic activity
To control the activity of the enzymes makes it possible to control the metabolism of the cell. This activity strongly depends on the conformation of the enzyme (and thus of the form of its sites), which can be modified via phosphorylations and déphosphorylations. Certain enzymes are active when they are phosphorylées, others when they are déphosphorylées. In fact other enzymes control phosphorylations and déphosphorylations: the Kinase S make it possible to transfer a grouping phosphates on their substrate, whereas phosphatases remove a grouping phosphates with their substrate.
The phosphorylation/dephosphorylation is a regulation where the enzyme is modified in a covalent way . Another type of important regulation which does not imply that the reversible fixing of an effector is the Allostérie.
Classification and denomination of the enzymesThe enzymes are classified in six independent groups, according to the type of reaction which they catalyze:
- Oxydoréductase S (EC. 1);
- Transférase S (EC. 2);
- Hydrolase S (EC. 3);
- Lyase S (EC. 4);
- Isomérase S (EC. 5);
- Ligase S (EC. 6).
- Nuclease S (EC. 7).
- Protease S (EC. 8).
- Synthétase S (EC. 9).
The enzymes are generally named by adding the suffix - ESA in the name of their substrate, and they are classified by a standard numerical system. Their number is allotted by the “Enzyme Commission” (EC.) to see Classification EC..
- allosteric enzyme : multimeric enzyme whose activity is controlled by a molecule not substrate.
- enzyme of the food transformation : enzyme employed to control texture, the taste, the aspect or the food value of food. The amylases degrade the simpler sugar complexes polysaccharidic; and the proteases “tenderize” proteins of the meat. An important objective of food biotechnology is the development of new food enzymes improving quality of the transformation of food.
- Enzyme of restriction or endonucléase of restriction : classify enzymes which cut the DNA after having recognized a specific sequence. The three types of endonucléase of restriction are:
- inductible enzyme : enzyme which is synthesized only in the presence of the substrate, or of a close molecule, which acts like inductor.
- repressible enzyme : enzyme whose activity can be reduced by the presence of a regulating molecule.
- enzyme limiting speed : enzyme whose activity controls the output of the finished product of a metabolic Voie multi-enzymatic…
- constitutive enzyme : enzyme whose concentration in the cell is constant and is not influenced by a concentration in substrate.
- a video educational on a molecule inhibiting the action of an enzyme, the NEP, to control the transmission of the pain
- a database on the enzymes: BRENDA.
- Visualization of enzymes in 3D
Simple: Enzyme Zh-min-nan: Kàⁿ-sò͘
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