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Enzymes availability

A competitive inhibitor and substrate exert reciprocal effects on the concentration of the EI and ES complexes. Since binding substrate removes free enzyme available to combine with inhibitor, increasing the [S] decreases the concentration of the EI complex and raises the reaction velocity. The extent to which [S] must be increased to completely overcome the inhibition depends upon the concentration of inhibitor present, its affinity for the enzyme K-, and the of the enzyme for its substrate. [Pg.68]

A second ternary complex reaction mechanism is one in which there is a compulsory order to the substrate binding sequence. Reactions that conform to this mechanism are referred to as bi-bi compulsory ordered ternary complex reactions (Figure 2.13). In this type of mechanism, productive catalysis only occurs when the second substrate binds subsequent to the first substrate. In many cases, the second substrate has very low affinity for the free enzyme, and significantly greater affinity for the binary complex between the enzyme and the first substrate. Thus, for all practical purposes, the second substrate cannot bind to the enzyme unless the first substrate is already bound. In other cases, the second substrate can bind to the free enzyme, but this binding event leads to a nonproductive binary complex that does not participate in catalysis. The formation of such a nonproductive binary complex would deplete the population of free enzyme available to participate in catalysis, and would thus be inhibitory (one example of a phenomenon known as substrate inhibition see Copeland, 2000, for further details). When substrate-inhibition is not significant, the overall steady state velocity equation for a mechanism of this type, in which AX binds prior to B, is given by Equation (2.16) ... [Pg.44]

Inhibition Effects in Enzyme Catalyzed Reactions. Enzyme catalyzed reactions are often retarded or inhibited by the presence of species that do not participate in the reaction in question as well as by the products of the reaction. In some cases the reactants themselves can act as inhibitors. Inhibition usually results from the formation of various enzyme-inhibitor complexes, a situation that decreases the amount of enzyme available for the normal reaction sequence. The study of inhibition is important in the investigation of enzyme action. By determining what compounds behave as inhibitors and what type of kinetic patterns are followed, it may be possible to draw important conclusions about the mechanism of an enzyme s action or the nature of its active site. [Pg.231]

High selectivity and substrate specificity of glycosyl transferases make them valuable catalysts for special linkages in polymer-supported synthesis. There is, however, still a rather limited set of enzymes available to date, and the need to synthesize a variety of natural and non-natural oligosaccharides prevails. Particularly with regard to combinatorial approaches, chemical solid-phase oligosaccharide synthesis promises to meet the demands most effectively. [Pg.11]

In silico methods able to highlight the most likely position(s) for conjugation may facilitate the development of new molecular scaffold with decreased U GT sensitivity, thus making the compounds more resistant to UGT conjugation. This may be another route for the development of more effective compounds, made possible by additional structural information on UGT enzymes available (Figure 12.2). [Pg.281]

Assays with Crude Extracts. Assays of the activities present in crude culture extracts were useful to indicate the enzymes available for recovery. Extracts from L. edodes typically exhibited a wide range of enzyme activities present in quantities apparently sufficient for isolation and characterization (Table I). [Pg.99]

Reversible inhibitors are potentially less damaging. In the presence of a reversible inhibitor, the enzyme activity decreases, but to a constant level as equilibrium is reached. The enzyme activity reflects the lower level of enzyme available for catalysis. We can subdivide the reversible inhibition into three types, i.e. competitive, non-competitive, and allosteric inhibition. [Pg.531]

This is a papaya enzyme available over the counter. It is not known whether this does anything. Dr. Grow said that Papain is an antibody to THC, and in theory may destroy THC when added to the urine sample. However, positive urine doesn t actually contain THC it contains THC byproducts. Papain has not been tested, and may or may not work. [Pg.55]

L A. When one inhibits the action of a drug-metabolizing enzyme (A), one would expect an increase instead of a decrease in drug concentrations, since less is being metabolized. Induction of an enzyme (B) would have the opposite effect, since there would be more enzyme available to metabolize the drug. [Pg.46]

As mentioned in part 2.1.3 hydrolytic enzymes are the most frequently used enzymes in organic chemistry. There are several reasons for this. Firstly, they are easy to ttse because they do not need cofactors like the oxidoreductases. Secondly, there are a large amormt of hydrolytic enzymes available because of their industrial interest. For instance detergent enzymes comprise proteases, celltrlases, amylases and lipases. Even if hydrolytic enzymes catalyse a chemically simple reaction, many important featirres of catalysis are still contained such as chemo-, regio- and stereoselectivity and specificity. [Pg.22]

Another important characteristic of M AOIs is the production of reversible versus irreversible enzyme inhibition. An irreversible inhibitor permanently disables the enzyme. This means that MAO must be resynthesized, in the absence of the drug, before the activity of the enzyme can be reestablished. Resynthesis of the enzyme may take up to 2 weeks. For this reason, an interval of 10-14 days is required after discontinuing irreversible inhibitors and before instituting treatment with other antidepressants or permitting the use of contraindicated drugs or the consumption of contraindicated foods. On the other hand, a reversible inhibitor can move away from the active site of the enzyme, making the enzyme available to metabo-hze other substances. The reversibility and selectivity of the currently available MAOIs are summarized in Table 2-4. [Pg.47]

Use the system with the greatest number of enzymes available. This will allow the development of as complete a picture of hepatic metabolism as possible. [Pg.188]

The wide variety of enzymes available gives for promise enzymatic derivatization to become a potent analytical tool in the future. Better understanding and theoretical formulations will lead to commercial availability of immobilized enzymes and consequently to more ready use of them. Since in such systems a low content of organic cosolvent in the mobile phase can only be tolerated (whereas a compromise has to be made as far as the optimum mobile phase pH is concerned), artificial enzymes, which are synthetic polymer chains having functional groups that mimic the biocatalytic activity of natural enzymes, are currently being synthesized and investigated as a means to overcome such limitations (276). [Pg.652]

With the active site residues identified and a detailed structure of the enzyme available, the path to understanding the reaction mechanism seemed open in the 1960s. However, definitive evidence for a particular mechanism eluded investigators for nearly four decades. There are two chemically reasonable mechanisms that could generate the observed product of lysozyme-mediated cleavage of the glycosidic bond. Phillips and... [Pg.222]

Since a competitive inhibitor has a strong structural resemblance to the substrate, both the inhibitor and substrate compete for the active site of an enzyme. The formation of an enzyme-inhibitor complex reduces the amount of enzyme available for interaction with the substrate and, as a result, the rate of reaction decreases. A competitive inhibitor normally combines reversibly with enzyme. Therefore, the effect of the inhibitor can be minimized by increasing the substrate concentration, unless the substrate concentration is greater than the concentration at which the substrate itself inhibits the reaction. The mechanism of competitive inhibition can be expressed as follows ... [Pg.32]

Table 13.2 summarises the different approaches used to construct enzyme electrochemical biosensors for application to food analysis based on the different types of enzymes available. Generally, the main problems of many of the proposed amperometric devices have been poor selectivity due to high potential values required to monitor the enzyme reaction, and poor sensitivity. Typical interferences in food samples are reducing compounds, such as ascorbic acid, uric acid, bilirubin and acetaminophen. Electrocatalysts, redox mediators or a second enzyme coupled reaction have been used to overcome these problems (see Table 13.2), in order to achieve the required specifications in terms of selectivity and sensitivity. [Pg.260]

Thus, every El complex reduces the amount of enzyme available for catalysis, regardless of where the inhibitor binds. As shown in Eq. (2.60), inhibition is a reversible process. The degree of reversibility depends on the ratio k k i or in other words, on the inhibitor binding equilibrium constant, K . [Pg.68]


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See also in sourсe #XX -- [ Pg.342 ]

See also in sourсe #XX -- [ Pg.1468 ]




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