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An inhibitor ( Latin for inhibere , to stop, to stop) is an inhibitor , i.e. a substance that influences one or more reactions - chemical, biological or physical - so that they are slowed down, inhibited or prevented. Inhibitors are used in particular in enzyme kinetics as enzyme-inhibiting substances, but also in chemistry and technology.

Inhibitors in biochemistry, pharmacology and toxicology

Many inhibitors inhibit or delay the conversion of biochemical substances, i.e. enzyme reactions . Depending on the type of inhibitor, different forms of inhibiting enzyme reactions are distinguished:

Most of these inhibitions are reversible, that is, they can be reversed. Irreversible inhibitions occur in the area of poisoning , for example in the case of poisoning by cyanides .

The reversible escapements are divided into:

  • Competitive inhibitions : Here the inhibitor competes with the substrate (the substance to be converted). This can be used in medicine.
  • Allosteric inhibitions : Here the inhibitor changes the molecular structure of the enzyme so that the substrate can no longer be bound and therefore cannot be converted.

A special form of allosteric inhibition is product inhibition. With this type of inhibition, the product intervenes in a self-regulating manner in the enzymatic process by inhibiting an enzyme. One example is cholesterol biosynthesis .

Inhibitors in microbiology

In microbiology , the term inhibitor is used for substances that inhibit or delay bacterial growth . For example, nutrient media can contain an addition of inhibitors that suppress the growth of one group of bacteria , while other types of bacteria can be selectively cultivated with them. Such nutrient media are therefore often selective media , for example MacConkey agar or XLD agar for the isolation and differentiation of gram-negative Enterobacteriaceae . Either antibiotics or certain dyes such as crystal violet or brilliant green are used as inhibitors to inhibit gram-positive bacteria .

Inhibitors are also used in the field of the microbiological analysis of milk , milk products and other foods of animal origin. In the milk quality regulation in § 3 stipulates that the delivered for processing milk no detectable inhibitors may be included. This can include antibiotics, cleaning agents , disinfectants and preservatives that inhibit lactic acid bacteria , so that, for. B. processing into yoghurt does not succeed. In a microbial screening the investigation carried out on inhibitors in milk or other foods. This is done, for example, with bacterial reduction tests (BRTs) or with the help of gel nutrient media in plate form, on which a test bacterium normally develops into a so-called bacterial lawn. The samples to be examined are applied in a suitable form to this nutrient medium gel. If inhibitors are contained in a sample , the growth of the test bacterium is hindered at the sample application site and in a diffusion zone around it (formation of an inhibition zone ). Such tests are known as inhibitor tests or agar diffusion methods . A similar examination in the medical field is the antibiogram .

Inhibitors in medicine

Inhibitory antibodies which are formed against the substituted coagulation factor VIII are a dreaded complication in haemophilia (blood disease); they reduce the effectiveness of this factor, which is why high-dose substitution is often necessary. Sometimes they also lead to a complete loss of effectiveness.

Inhibitors in Chemistry

Chemical inhibitors (passivators, inhibitors, retarders , anti-catalysts, negative catalysts) are z. B. used to prevent oxidative changes in food (→ antioxidants ) or to control the rate of polymerisation . In macromolecular chemistry, inhibitors, like Allen , are also used to stop polymerization and to make statements about the relative concentration of active centers (points at which the polymerization proceeds dynamically). When processing plaster of paris or concrete, retarders are added to prevent these building materials from setting too quickly. A plaster of paris that already contains the retarder is marketed under the trade name Moltofill ® . In catalytic processes, inhibitors act as catalyst poisons , for example lead in vehicle catalysts .

In the petrochemical industry , various inhibitors are added to crude oil or natural gas in order to prevent gas hydrates from settling on their walls during transport through pipelines , which can lead to a lower flow rate due to the increased pressure drop and clog valves .

Inhibitors in electrochemistry

In electrochemistry , inhibitors u. a. used to protect surfaces from corrosion . This store by adsorption z. B. organic molecules on the surface and block reactions with the environment. VCI agents ( Volatile Corrosion Inhibitors ) are widely used as temporary protection for corrosion inhibitors . In closed systems such as B. cooling circuits , corrosion inhibitors can be added to the medium.

Inhibitors in Technology

In heating and air conditioning technology as well as in steam technology , inhibitors are added to the cooling and heating circuit or, in general, to the water circuit . This prevents undesirable reactions ( e.g. corrosion ). One of the additives is hydrazine , N 2 H 4 , which binds the oxygen present in the water or wet steam, releasing nitrogen dioxide . The addition of hydrazine results in strongly alkaline solutions with a pH value of 12 to 13, which make the safety devices necessary for alkaline solutions.

Hydrazine is currently used as a conditioning agent for the treatment of feedwater in power plants. However, its use is limited to high-pressure systems or systems in the hypercritical area. Substitutes are already being used successfully at operating pressures of up to 125 bar.

In food technology, hydrazine may only be used if the permissible limit values ​​are not exceeded.

A many lubricants added additive is a so-called corrosion inhibitor, whose task it is, for metallic surfaces. B. in engines to protect against corrosion.

Inhibitors in fire fighting

In fire fighting, inhibitors of fire classes B and C are very often used in the form of extinguishing powder (heterogeneous inhibition) and now also occasionally in the form of halons (homogeneous inhibition).

See also

Individual evidence

  1. ^ Siegfried Ebel, Hermann J. Roth (Ed.): Lexicon of Pharmacy. Georg Thieme, Stuttgart et al. 1987, ISBN 3-13-672201-9 , p. 338.
  2. Eckhard Bast: Microbiological Methods: An Introduction to Basic Working Techniques . 2nd Edition. Spectrum Akademischer Verlag GmbH, Heidelberg / Berlin 2001, ISBN 978-3-8274-1072-6 , p. 149-150 .
  3. a b Klaus Pichhardt: Food Microbiology: Fundamentals for practice . 1st edition. Springer Verlag, Heidelberg / Berlin 1984, ISBN 3-540-13522-7 , pp. 70-76 .
  4. Karl Zickrick et al. a .: Microbiology of animal foods. An introduction . 2nd Edition. Verlag Harri Deutsch, Frankfurt 2001, ISBN 3-87144-633-5 , p. 36-40, 96-100 .
  5. ^ Brockhaus ABC chemistry. Volume 1: A - K. VEB FA Brockhaus-Verlag, Leipzig 1965, p. 579.
  6. ^ Manfred Dieter Lechner, Klaus Gehrke, Eckhard H. Nordmeier: Makromolekulare Chemie. 4th, revised and expanded edition. Birkhäuser, Basel et al. 2010, ISBN 978-3-7643-8890-4 , p. 98.