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Enzyme interaction with substrate

Enzymes are proteinaceous substances with highly specific structures that interact with particular substances or classes of substances called substrates. Enzymes act as catalysts to enable biochemical reactions to occur, after which they are regenerated intact to take part in additional reactions. The extremely high specificity with which enzymes interact with substrates results from their lock and key action, based on the unique shapes of enzymes, as illustrated in Figure 3.10. [Pg.89]

A chemical that alters color as a result of an enzyme interaction with substrate. [Pg.11]

Induced fit model A model for how enzymes interact with substrates to achieve catalysis. According to this model, the... [Pg.1147]

Induced Fit Model A model for how enzymes interact with substrates to achieve catalysis. According to this model, the empty active site of the enzyme only roughly fits the substrate(s), and the entry of substrate causes the enzyme to change its shape so as to both tighten the fit and causes the substrate to adopt an intermediate state that resembles the transition state of the uncatalyzed reaction. This is currently the dominant model for enzymatic catalysis. [Pg.901]

Figure 8.2 Enzyme interaction with two enantiomers of a given substrate molecule. Figure 8.2 Enzyme interaction with two enantiomers of a given substrate molecule.
The binding of a substrate to its active center was first postulated by E. Fisher in 1894 using the lock and key mechanism which states that the enzyme interacts with its substrate like a lock and a key, respectively, i.e. the substrate has a matching shape to fit into the active site. This theory assumed that the structure of the catalyst was completely rigid and could not explain why the macromolecule was able to catalyze reactions involving large substrates and not those with small ones, or why they could convert non natural compounds with different structural properties to the substrate. [Pg.329]

Extensive studies have established that the catalytic cycle for the reduction of hydroperoxides by horseradish peroxidase is the one depicted in Figure 6 (38). The resting enzyme interacts with the peroxide to form an enzyme-substrate complex that decomposes to alcohol and an iron-oxo complex that is two oxidizing equivalents above the resting state of the enzyme. For catalytic turnover to occur the iron-oxo complex must be reduced. The two electrons are furnished by reducing substrates either by electron transfer from substrate to enzyme or by oxygen transfer from enzyme to substrate. Substrate oxidation by the iron-oxo complex supports continuous hydroperoxide reduction. When either reducing substrate or hydroperoxide is exhausted, the catalytic cycle stops. [Pg.317]

The active site is a specialized region of the protein where the enzyme interacts with the substrate. [Pg.94]

While cytochrome P-450 catalyzes the interaction with substrates, a final step of microsomal enzymatic system, flavoprotein NADPH-cytochrome P-450 reductase catalyzes the electron transfer from NADPH to cytochrome P-450. As is seen from Reaction (1), this enzyme contains one molecule of each of FMN and FAD. It has been suggested [4] that these flavins play different roles in catalysis FAD reacts with NADPH while FMN mediates electron... [Pg.764]

It would appear that the specific action of an enzyme upon its substrate is conditioned by a definite chemical structure and spatial arrangement of the constituent polar and non-polar groups of the enzyme protein as well as by the constitution and configuration of the substrate. In some cases an enzyme interacts with one chemical compound only. For example, galactokinase extracted from Saccharomyces fragilis (grown on whey) catalyzes the transphosphorylation between adenosine triphos-... [Pg.62]

For the Michaelis-Menten scheme involving interaction of enzyme (E) with substrate (S) or product (P) ... [Pg.61]

The flavin-based coenzymes flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN) are associated with a wide variety of enzymes that catalyze reactions in critical biosynthetic and catabolic processes (Fig. 16). Unlike other coenzymes, the reactions catalyzed do not conserve specific mechanistic pathways. In each case the apoenzyme serves to steer the course of the reaction through specific interactions with substrate and coenzyme [55]. Nonetheless, there are common features of the interactions of the apoenzymes with the flavin which can be exploited in the design of functional peptides and proteins. [Pg.23]

Because of its substantial inhibition of CYP 3A3/4, this antidepressant is prone to pharmacokinetic drug-drug interactions with substrates for this enzyme ( Table 7-30). That is important because CYP 3A3/4 is responsible for approximately 50% of all known drug metabolism. Thus, there are a number of medications that either... [Pg.156]

The search for selective means of inactivation, prompted by clinical considerations, has not been successful, although many substrate analogs act as powerful competitive inhibitors 8). On the other hand, irreversible inhibition may result from interaction with substrate analogs which cause labilization of the enzyme (see Section IV,B). Specific stimulation and inhibition by homologous antibodies is reviewed in Section V. [Pg.43]

The variable activity of RNase toward different RNA preparations has been tracked down in part to the variable metal content of the substrates [see Wojnar and Roth (4-76), and earlier references quoted]. Takahashi et al. (477) have reported that Mg2+, Ca2+, and Mn2+ have little or no effect on step 1 or step 2 activity when these are assayed with low molecular weight substrates. However, Ca2+ and Mg2+ do interact with RNA and they inhibit the RNase-catalyzed reaction at pH 7 because of this interaction with substrate (478). Eichhorn et al. (479) found activation by Mg2+ and various transition metals at pH 5. In any event it is clear that in general each metal can be expected to show different effects as a function of pH, ionic strength, specific buffer effects, etc. A substantial correlation of much of the data has been made by Alger (480) who studied RNA and C > p substrates over wide ranges of metal concentration. Activation appeared to involve predominantly metal-substrate interactions while inhibition occurred with direct enzyme-metal interaction. [Pg.770]


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See also in sourсe #XX -- [ Pg.81 ]

See also in sourсe #XX -- [ Pg.81 ]




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