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Enzymatic Reaction Kinetics
Published in Debabrata Das, Debayan Das, Biochemical Engineering, 2019
The pH of the reaction mixture largely affects the enzymatic reaction. It may be noted that there is an optimum pH for each enzyme. For example, stomach has the enzyme pepsin, which has an optimum pH between 2 and 3.3, while the optimum pH of amylase, from saliva, is 6.8. Chymotrypsin, from the pancreas, has an optimum pH in the mildly alkaline region between 7 and 8. Enzymes are protein consisting of amino acid residues. The pH of such solutions may be acidic, basic, or neutral based on the negative or positive charge. For example, glutamic acid is acidic at a lower pH, and the increase in pH ionizes glutamic acid. On the other hand, an amino acid lysine is basic in the range of higher pH value. As the pH is decreased, lysine is ionized. An enzyme is catalytically active when each of the amino acid residues at the active site possesses a particular charge. Therefore, the fraction of the catalytically active enzyme depends on the pH.
Enzyme Catalysis
Published in Harvey W. Blanch, Douglas S. Clark, Biochemical Engineering, 1997
Harvey W. Blanch, Douglas S. Clark
Chymotrypsin is a serine protease that cleaves the amide linkages in proteins and peptides. It has a binding pocket which is selective for the aromatic residues of amino acids. The reaction occurs by the reversible formation of a Michaelis complex, followed by acylation of Ser-195 to give a tetrahedral acylenzyme intermediate (this is shown in detail later in Figure 1.8). Chymotrypsin will also act as an esterase; we can write the elementary reaction steps in the following form, where RCO-X is an amide or an ester E+RCO-X⇔RCO-X⋅E→k2RCO-E+XH→k3RCOOH+E
α-Chymotrypsin-catalyzed synthesis of 2-substituted benzimidazole through retro-Claisen reaction
Published in Green Chemistry Letters and Reviews, 2018
Lian-Sheng Liu, Zong-Bo Xie, Can Zhang, Lei-Han Fu, Hai-Bo Zhu, Zhang-Gao Le
α-Chymotrypsin belongs to the family of serine proteases and is a polypeptide chain consisting of 245 amino acids; His-57, Asp-102, and Ser-195 constitute the catalytic triad (42–44). Combining this information and our part work (45), we purpose a plausible mechanism, as illustrated in Scheme 1. Initially, nucleophilic addition occurs to form intermediate imino ester A, in which the proton from the amido group of o-phenylenediamine may be abstracted by His 57 and the carbonyl of the ketone is effectively activated by Ser-195 (46,47). Subsequently, A undergoes cyclization to form aminal B along with the removal of water. In the presence of a His-57, the corresponding benzimidazole is produced by retro-Claisen reaction, along with regeneration of α-chymotrypsin to complete the catalytic cycle.