Enzymatic reaction scheme

In the course of the enzymatic reactions (Scheme 8) neither the C-terminal methyl ester nor the base labile thioester was effected.1111... 

The simplest possible enzymatic reaction scheme was proposed in 1913 by Michealis and Menten. They assumed the molecule undergoing reaction (the substrate, S) is adsorbed reversibly on a specific site of the enzyme E to form a complex ES whose decomposition into product P is rate controlling. The scheme resembles that for unimolecular decomposition (see Chapter 14). 

Since none of the liposomal immunoassay approaches described in the scientific literature thus far took advantage of surface immobilization techniques, one could envision a double-amplification biosensor in which surface modification plays an important role [35]. For example, consider a dehydrogenase enzyme marker system which requires an electroactive cofactor such as NAD+. In the enzymatic reaction scheme ... 

Compound 13 represent a transition state analogue of the A-acetylneuraminyl cation during the enzymatic reaction (Scheme 3). According to a postulate by L. Pauling compounds that closely resemble the transition state have higher binding affinity toward the... 

It is important to note that this mechanism conforms to the pathway of the enzymatic reaction (Scheme 2). The activity of the complex is controlled... 

The chemical model for a kinetic investigation is a set of reaction equations which describe the process under investigation. Consider as an example the basic enzymatic reaction scheme... 

Although the mechanisms may be complicated and varied, some simple equations can often describe the reaction kinetics of common enzymatic reac tions qiiite well. Each enzyme molecule is considered to have an active site that must first encounter the substrate (reactant) to form a complex so that the enzyme can function. Accordingly, the following reaction scheme is written ... 

Figure 8.6 Reaction schemes for the production of L-phenylalanine by enzymatic methods.

Consider reaction schemes for the production of L-phenylalanine by enzymatic methods. Now match each of the following substrates with the enzyme(s) responsible for L-phenylalanine formation. 

Typical single-substrate enzymatic reactions can be described by the kinetic scheme (see Refs. 1 and 2 for more extensive discussions). 

Surprisingly, the 7t-system geometry in a substrate has a notable influence in the enzymatic aminolysis of esters. The reaction of diethyl fumarate with different amines or ammonia in the presence of CALB led to the corresponding trans-amidoesters with good isolated yields, but in the absence of enzyme, a high percentage of the corresponding Michael adduct is obtained (Scheme 7.9). Enzymatic aminolysis of diethyl maleate led to the recovery of the same a, P-unsaturated amidoester, diethyl fumarate, and diethyl maleate. The explanation of these results can be rationalized via a previous Michael/retro-Michael type isomerization of diethyl maleate to fumarate, before the enzymatic reaction takes place. In conclusion, diethylmaleate is not an adequate substrate for this enzymatic aminolysis reaction [23]. 

The pentagon stabilization has been found in a biochemical phenomenon [80], The hydrogen on the thiazolium ring 9 (Scheme 7) is easily ionized to afford the corresponding carbene 10, a key catalyst in enzymatic reactions for which thiamine (vitamin B-1,11) pyrophosphate is the cofactor. The pentagon stability is expected to contribute to this unusual deprotonation. A lone pair generated on the carbon atom in 10 can similarly delocalize through the vicinal C-N and C-S a bonds in a cyclic manner. 

Figure 5.3 A convenient scheme for performing an inhibitor titration in 96-well format. Four compounds (1-4) are assessed in duplicate at each of 11 inhibitor concentrations. The inhibitor concentrations follow a threefold serial dilution from a maximum concentration of 1000 (molarity units nM, LlM, etc.). The right most column of wells is reserved for control samples. In this illustration four of the wells of column 12 are used for zero inhibitior positive controls, and the other four are used to establish the assay background as negative controls. Negative controls could represent any sample for which one knows that the enzymatic reaction has be abrogated. For example, the negative control wells could contain all of the reaction mixture components except the enzyme. See Chapter 4 for other potential forms of negative controls.

Figure 6.2 Effect of preincubation time with inhibitor on the steady state velocity of an enzymatic reaction for a very slow binding inhibitor. (A) Preincubation time dependence of velocity in the presence of a slow binding inhibitor that conforms to the single-step binding mechanism of scheme B of Figure 6.3. (B) Preincubation time dependence of velocity in the presence of a slow binding inhibitor that conforms to the two-step binding mechanism of scheme C of Figure 6.3. Note that in panel B both the initial velocity (y-intercept values) and steady state velocity are affected by the presence of inhibitor in a concentration-dependent fashion.

Step 1. An enzymatic reaction is considered as a cyclic process that displays all the interconversions among the various enzyme forms involved. For each step in the reaction a rate constant is defined in terms of the product of the actual rate constant for that step and the concentration of free substrate involved in the step. Hence, the cyclic form of the reaction scheme given in Equations 17.6, 17.7, and 17.8 is represented by... 

Figure 14.9 Reaction scheme for production of (—)-ephedrine based on enzymatic C—C bond formation using Saccharomyces cerevisiae coupled with a chemical reductive animation...

An interesting procedure has been proposed for the synthesis of amylose-b-PS block copolymers through the combination of anionic and enzymatic polymerization [131]. PS end-functionalized with primary amine or dimethylsilyl, -SiMe2H groups were prepared by anionic polymerization techniques, as shown in Scheme 56. The PS chains represented by the curved lines in Scheme 56 were further functionalized with maltoheptaose oligomer either through reductive amination (Scheme 57) or hydrosilyla-tion reactions (Scheme 58). In the first case sodium cyanoborohydride was used to couple the saccharide moiety with the PS primary amine group. 

FIA has also found wide application in pharmaceutical analysis.214,215 Direct UV detection of active ingredients is the most popular pharmaceutical analysis application of FIA. For single component analysis of samples with little matrix interference such as dissolution and content uniformity of conventional dosage forms, many pharmaceutical chemists simply replace a column with suitable tubing between the injector and the detector to run FIA on standard HPLC instrumentation. When direct UV detection offers inadequate selectivity, simple online reaction schemes with more specific reagents including chemical, photochemical, and enzymatic reactions of derivatization are applied for flow injection determination of pharmaceuticals.216... 

Fig. 19. Reaction scheme for the electrochemically driven enzymatic carboxylation of acetyl-SCoA to form pyruvic acid...

Since the enzymatic reactions are generally rapid, it may be assumed that the steady-state approximation applies. Note, however, that although true is most systems, this is not always the case, as exemplified in Section 5.2.5. Each half-reaction is characterized by three rate constants, defined in Scheme 5.1. They may alternatively be characterized by the following... 

Though the assumption of an irreversible dissociation of the product considerably simplifies the mathematical analysis, all enzymatic reactions are inherently reversible. To account for the presence of a significant amount of product within the intracellular medium, we must allow the reverse reaction [96,140,157]. In this case, using an augmented scheme,... 

---