Search results
Results from the WOW.Com Content Network
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]
The distribution of known enzyme catalytic rates (k cat /K M). 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])
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).
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} }} .
Enzymes are generally in a state that is not only a compromise between stability and catalytic efficiency, but also for specificity and evolvability, the latter two dictating whether an enzyme is a generalist (highly evolvable due to large promiscuity, but low main activity) or a specialist (high main activity, poorly evolvable due to low ...
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 enzymes from these two sources are 34% homologous, and structural studies have shown that the placement of the catalytic groups in the active sites is virtually identical. [3] Mammalian KSI has been studied from bovine adrenal cortex [4] and rat liver. [5] This enzyme participates in c21-steroid hormone metabolism and androgen and estrogen ...