Sequential, enzymatic reaction

Prostaglandin endoperoxide H2 synthase (PGHS) [EC 1.14.99.1] isoenzymes 1 and 2 catalyze the committed step in prostanoid synthesis via two sequential enzymatic reactions... 

The ubiquitinylation of proteins is a complex process, which involves three sequential enzymatic reactions performed by three types of enzymes, El, E2 and E3 (Fig. 2.9). The enzymatic conjugating cascade is organized in a hierarchical way There is one El enzyme, a limited number of E2 enzymes, each of which may serve several E3 enzymes, and a much larger number of E3 enzymes (Fig. 2.10). 

Flo. 61. (A) Sequential enzymatic reactions of acetylcholine and choline to HjOj. (B) Chromatogram from rat brain homogenate 126 pmolofcholine(Ch)and 329 pmolr acetyl-choline (ACh) found. Detection as H on Pt electrode at +0.5 V versus Ag/AfO. 

This chapter reviewed some of our group s contributions to the development and application of QM/MM methods specifically as applied to enzymatic reactions, including the use of sequential MD/QM methods, the use of effective fragment potentials for reaction mechanisms, the development of the new QM/MM interface in Amber, as well as the implementation and optimization of the SCC-DFTB method in the Amber program. This last implementation allows the application of advanced MD and sampling techniques available in Amber to QM/MM problems, as exemplified by the potential and free energy surface surfaces for the reaction catalyzed by the Tripanosoma cruzi enzyme /ram-sialidasc shown here. 

The catalytic cycle of laccase includes several one-electron transfers between a suitable substrate and the copper atoms, with the concomitant reduction of an oxygen molecule to water during the sequential oxidation of four substrate molecules [66]. With this mechanism, laccases generate phenoxy radicals that undergo non-enzymatic reactions [65]. Multiple reactions lead finally to polymerization, alkyl-aryl cleavage, quinone formation, C> -oxidation or demethoxylation of the phenolic reductant [67]. 

Thus far only reactions involving a single substrate have been considered. Most enzymatic reactions have two substrates. Unlike chemical processes, the sequence in which the substrates bind to the enzyme may be important. If two substrates, A and B, bind in a specific order (e.g., A binds first) as illustrated in Equation 11.37 the mechanism is called ordered sequential. 

Rubber molecules are synthesized from one APP molecule, which initiates the reaction, and the rubber polymer (cw-l,4-polyisoprene) is then polymerized by sequential condensations of the non-allylic IPP (magnesium cations are a required cofactor) with release of a diphosphate at each condensation. After initiation and elongation, a termination event occurs in which the rubber molecule is released from the enzyme. Despite the similar process, remarkable differences exist between plant species with respect to enzymatic reaction mechanisms and product molecular weight. 

The ubiquitinylation of proteins is a complex process which involves several specific enzymatic reactions. Three sequential steps can be distinguished (fig. 2.15A) ... 

Detection launch the detection in Immusoft in order to follow the enzymatic reaction by chrono-amperometry at 250 mV versus Ag/AgCl (sequential detections of 2 s of potential application performed in each channel one after the other). 

Sequential one-pot synthesis Reactions occur sequentially Variable reaction conditions (e.g., pH, T°C) No isolation of intermediate products Regioselective enzymatic protection and chemical acetylation 15... 

Multi-step technique (3) This is an indirect/direct method combining unlabeled primary antibodies with directly-conjugated antibodies. The method starts with staining the unlabeled antibody/antibodies with the appropriate detection system, but without performing the final enzymatic staining reaction. The tissue is blocked with normal serum from the host of the first primary antibody before the second, directly-labeled primary antibody is added. The staining ends with the two enzymatic reactions being performed sequentially. 

The bacterial enzyme chorismate mutase-prephenate dehydrogenase is peculiar because it is a single protein unit with two catalytic activities. It catalyzes the sequential reactions of mutation of chorismate to prephenate and then the reaction that leads to the formation of phenylalanine and tyrosine, through oxidation of prephenate. The first of these reactions is interesting because it is one of the few strictly single-substrate enzymatic reactions it entails... 

Enzymatic reactions, despite the obvious energy preference of certain concerted mechanisms, may be inefficient because of a too low synchronization factor. In such cases, the sequential transformation of the system through a number of steps is favorable. Here, the role of a multi-functional catalyst, in reaching a pretransition state is to provide favorable energy and synchronization factors through the optical use of the corresponding functional groups at each step of the process. 

Enzymatic reactions can be assayed in different ways. The availability of automated high-pressure liquid chromatography (HPLC) and gas-liquid chromatography (GLC) has made the sequential analysis of several hundred reactions practical [55]. Virtually... 

Prodrug activation occurs enzymatically, non-enzymatically, or sequentially (enzymatic step followed by non-enzymatic rearrangement). As much as possible, it is desirable to reduce biological variability, hence, the particular interest currently received by non-enzymatic reactions of intramolecular cyclization-eliminationf ... 

---