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In the field of biochemistry, the specificity constant (also called kinetic efficiency or /), is a measure of how efficiently an enzyme converts substrates into products.A comparison of specificity constants can also be used as a measure of the preference of an enzyme for different substrates (i.e., substrate specificity).
In chemistry, the term "turnover number" has two distinct meanings.. 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]
This constant is a measure of catalytic efficiency. The most efficient enzymes reach a k 2 / K M {\displaystyle k_{2}/K_{M}} in the range of 10 8 – 10 10 M −1 s −1 .
The specificity constant / (also known as the catalytic efficiency) is a measure of how efficiently an enzyme converts a substrate into product. Although it is the ratio of k cat {\displaystyle k_{\text{cat}}} and K m {\displaystyle K_{\mathrm {m} }} it is a parameter in its own right, more fundamental than K m {\displaystyle K_{\mathrm {m} }} .
Kinetically perfect enzymes have a specificity constant, k cat /K m, on the order of 10 8 to 10 9 M −1 s −1.The rate of the enzyme-catalysed reaction is limited by diffusion and so the enzyme 'processes' the substrate well before it encounters another molecule.
In organic chemistry, kinetic resolution is a means of differentiating two enantiomers in a racemic mixture.In kinetic resolution, two enantiomers react with different reaction rates in a chemical reaction with a chiral catalyst or reagent, resulting in an enantioenriched sample of the less reactive enantiomer. [1]
A catalytic triad is a set of three coordinated amino acid residues that can be found in the active site of some enzymes. [1] [2] Catalytic triads are most commonly found in hydrolase and transferase enzymes (e.g. proteases, amidases, esterases, acylases, lipases and β-lactamases).
Moreover, superoxide dismutase has the largest k cat /K M (an approximation of catalytic efficiency) of any known enzyme (~7 x 10 9 M −1 s −1), [24] this reaction being limited only by the frequency of collision between itself and superoxide. That is, the reaction rate is "diffusion-limited".