Active site


Active site

The active site of an enzyme contains the catalytic and binding sites. The structure and chemical properties of the active site allow the recognition and binding of the substrate.

The active site is usually a small pocket at the surface of the enzyme that contains residues responsible for the substrate specificity (charge, hydrophobicity, steric hindrance) and catalytic residues which often act as proton donors or acceptors or are responsible for binding a cofactor such as PLP, TPP or NAD. The active site is also the site of inhibition of enzymes (see Enzyme inhibitor article).

Models

There are two proposed models of how enzymes work: the lock-and-key model and the induced fit model. The lock-and-key model assumes that the active site is a perfect fit for a specific substrate and that once the substrate binds to the enzyme no further modification is necessary, this is simplistic. The induced fit model is a development of the lock and key model and instead assumes that an active site is more flexible and that the presence of certain residues (amino acids) in the active site will encourage the enzyme to locate the correct substrate, after which conformational changes may occur as the substrate is bound.

Substrates bindinsded to the active site of the enzyme or a specificity pocket through hydrogen bonds, hydrophobic interactions, temporary covalent bonds (van der waals) or a combination of all of these to form the enzyme-substrate complex. Residues of the active site will act as donors or acceptors of protons or other groups on the substrate to facilitate the reaction. In other words, the active site modifies the reaction mechanism in order to decrease the activation energy of the reaction. The product is usually unstable in the active site due to steric hindrances that force it to be released and return the enzyme to its initial unbound state.

ee also

* Enzyme catalysis
* Hugh Stott Taylor
* Catalytic triad
* Activity based proteomics


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Look at other dictionaries:

  • active site — n a region esp. of a biologically active protein (as an enzyme) where catalytic activity takes place and whose shape permits the binding only of a specific reactant molecule * * * the part of an enzyme or other catalyst at which the reaction… …   Medical dictionary

  • active site — active site. См. активный сайт. (Источник: «Англо русский толковый словарь генетических терминов». Арефьев В.А., Лисовенко Л.А., Москва: Изд во ВНИРО, 1995 г.) …   Молекулярная биология и генетика. Толковый словарь.

  • active site — aktyvusis centras statusas T sritis chemija apibrėžtis Labai veiklus molekulės arba katalizatoriaus fragmentas. atitikmenys: angl. active center; active site rus. активный центр …   Chemijos terminų aiškinamasis žodynas

  • active site — The part of an enzyme that binds the substrate to form an enzyme substrate complex and catalyze the reaction. Also called the catalytic site …   Dictionary of microbiology

  • active site — noun the part of an enzyme or antibody where the chemical reaction occurs • Hypernyms: ↑site, ↑situation • Part Holonyms: ↑enzyme, ↑antibody …   Useful english dictionary

  • active site — noun Date: 1957 a region on the surface of an enzyme whose shape permits binding only of a specific molecular substrate that then undergoes catalysis …   New Collegiate Dictionary

  • active site — The region of a protein that binds to substrate molecule(s) and facilitates a specific chemical conversion. Produced by juxtaposition of amino acid residues as a consequence of the protein s tertiary structure …   Dictionary of molecular biology

  • active site — Biochem. the part of an enzyme that interacts with the substrate during catalysis. [1960 65] * * * …   Universalium

  • active site — Location on a catalyst surface where reaction takes place …   Petroleum refining glossary

  • active site — noun Biochemistry a region on an enzyme that binds to and reacts with the substrate during a reaction …   English new terms dictionary


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