Optimum active site

If we remember that m= [Si]/[S2] (Eq. (2.122)), then the result of Eq. (2.174) simply and legibly tells us that the optimum active site or catalyst ought to have ... 

Enzymes are nature s catalysts. For the moment it is sufficient to consider an enzyme as a large protein, the structure of which results in a very shape-specific active site (Fig. 1.3). Flaving shapes that are optimally suited to guide reactant molecules (usually referred to as substrates) in the optimum configuration for reaction, enzymes are highly specific and efficient catalysts. For example, the enzyme catalase catalyzes the decomposition of hydrogen peroxide into water and oxygen... 

Another example of heterogeneous catalysis by oxo-ions is the one-step oxidation of benzene to phenol with nitrous oxide, N2O. Fe/MFI catalysts have, again been found to be very active. This catalysis was discovered by Iwamoto and has been extensively studied by the group of G. Panov in Novosibirsk. " Preparations of Fe/MFI which appear highly active for this reaction display poor activity for NOj reduction and those which are optimum for that process, are poor for benzene oxidation. This shows that different sites are used. Work by Jia et al. revealed that the active sites for benzene oxidation appear to be Fe-oxo-ions containing only one Fe ion. This does not necessarily mean that the sites are mononuclear. A recent work by Zhu et al. has rather suggested that the site consists of one Fe and one Al + ion, the latter ion having left the zeolite framework. ... 

At low ionic strength (0.01) the pH profile of the lytic reaction has an optimum at about 9.0-10.0, i.e., in a range where both carboxyl groups of the active site would be deprotonated and consequently the enzyme should be inactive. 

The study of the product distribution from the isomerization of 3,3-dimethylbutene proved useful for evaluating the strength of the acid centers in aluminas (36). Pure alumina from aluminum isopropoxide which was calcined at 700° showed optimum activity. Heating at higher temperatures decreased the number of acid sites as well as their acid strength. Aluminas obtained from potassium or sodium aluminate contained alkali in amounts of 0.08 to 0.65%, depending on the way of precipitation and on the number of washings. 

Enzymes are active over a limited pH range the pH value of maximum activity is known as the pH optimum, and this is characteristic of the enzyme. It typically reflects the pH necessary to achieve the appropriate ionization of amino acid side-chains at the active site. 

Plot of the fractional saturation of enzyme active sites (v/Wax) versus the reduced substrate concentration [S]/Ks where K/K = 1, 10, 30, and infinity. Notice that there is an optimum in the rate dependence on substrate concentration. 

An important parameter of glycosidase inhibition by basic sugar analogues is certainly the pKa value of the respective potential inhibitor in relation to the state of protonation of the active site under consideration, and the pH optimum of the enzyme. 

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