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In biology and biochemistry, the active site is the region of an enzyme where substrate molecules bind and undergo a chemical reaction. The active site consists of amino acid residues that form temporary bonds with the substrate, the binding site , and residues that catalyse a reaction of that substrate, the catalytic site .
The enzyme of high energy content may firstly transfer some specific energetic group X 1 from catalytic site of the enzyme to the final place of the first bound reactant, then another group X 2 from the second bound reactant (or from the second group of the single reactant) must be transferred to active site to finish substrate conversion to ...
The sophistication of the active site network causes residues involved in catalysis (and residues in contact with these) to be highly evolutionarily conserved. [62] However, many examples of divergent evolution in catalytic triads exist, both in the reaction catalysed, and the residues used in catalysis.
An example of an enzyme that contains a cofactor is carbonic anhydrase, which uses a zinc cofactor bound as part of its active site. [61] These tightly bound ions or molecules are usually found in the active site and are involved in catalysis. [1]: 8.1.1 For example, flavin and heme cofactors are often involved in redox reactions. [1]: 17
Enzyme catalysis of chemical reactions occur with high selectivity and rate. The substrate is activated in a small part of the enzyme 's macromolecule called the active site . There, the binding of a substrate close to functional groups in the enzyme causes catalysis by so-called proximity effects.
Most enzymes have a rate around 10 5 s −1 M −1. The fastest enzymes in the dark box on the right (>10 8 s −1 M −1) are constrained by the diffusion limit. (Data adapted from reference [1]) A diffusion-limited enzyme catalyses a reaction so efficiently that the rate limiting step is that of substrate diffusion into the active site, or ...
In enzymology, the turnover number (k cat) is defined as the limiting number of chemical conversions of substrate molecules per second that a single active site will execute for a given enzyme concentration [E T] for enzymes with two or more active sites. [1] For enzymes with a single active site, k cat is referred to as the catalytic constant ...
The structures of the active sites of the three types of hydrogenase enzymes. Hydrogenases catalyze, sometimes reversibly, H 2 uptake. The [FeFe] and [NiFe] hydrogenases are true redox catalysts, driving H 2 oxidation and proton (H + ) reduction (equation 3 ), the [Fe] hydrogenases catalyze the reversible heterolytic cleavage of H 2 shown by ...