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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 .
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).
To address such a paradox, Kuo-Chen Chou and his co-workers proposed a model by taking into account the spatial factor and force field factor between the enzyme and its substrate and found that the upper limit could reach 10 10 M −1 s −1, [6] [7] [8] and can be used to explain some surprisingly high reaction rates in molecular biology. [5 ...
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} }} .
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".
The rate of a reaction is the concentration of substrate disappearing (or product produced) per unit time (mol L −1 s −1).. The % purity is 100% × (specific activity of enzyme sample / specific activity of pure enzyme).
The reaction catalyzed by CA1 is the same as other carbonic anhydrase family proteins: + (in tissues - high CO 2 concentration) [9]. The CA1-catalyzed reaction has a relatively low reaction affinity (Km) of 4.0 mM for CO 2, [7] [10] turnover number (Kcat) of 2 × 10 5 s −1, and catalytic efficiency (Kcat/Km) of 5 × 10 7 M −1 s −1 comparing to other isozymes of the α-CA family of ...