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Equilibrium binding processes

Figure 5 An example calibration curve. Absorbance is plotted against log (concentration of analyte). The competitive equilibrium binding process results in a sigmoidal curve that is fitted using a four-parameter fit. The IC50 is defined as the concentration of analyte that results in a 50% inhibition of the absorbance... Figure 5 An example calibration curve. Absorbance is plotted against log (concentration of analyte). The competitive equilibrium binding process results in a sigmoidal curve that is fitted using a four-parameter fit. The IC50 is defined as the concentration of analyte that results in a 50% inhibition of the absorbance...
Thus, as described by Equation (2.1), the equilibrium dissociation constant depends on the rate of encounter between the enzyme and substrate and on the rate of dissociation of the binary ES complex. Table 2.1 illustrates how the combination of these two rate constants can influence the overall value of Kd (in general) for any equilibrium binding process. One may think that association between the enzyme and substrate (or other ligands) is exclusively rate-limited by diffusion. However, as described further in Chapter 6, this is not always the case. Sometimes conformational adjustments of the enzyme s active site must occur prior to productive ligand binding, and these conformational adjustments may occur on a time scale slower that diffusion. Likewise the rate of dissociation of the ES complex back to the free... [Pg.22]

Figure 14.13 The kinetic sequence of reactions that control the cyclic AMP concentration, and its binding to the effector system, and the kinetic sequence that controls the concentration of a neurotransmitter and its binding to the receptor on the postsyn-aptic membrane. Processes (1) are reactions catalysed by adenyl cyclase, and exocytosis. Reactions (2) are catalysed by phosphodiesterase and, for example, acetylcholinesterase. Reactions (3) are the interactions between the messenger and the effector system both the latter are equilibrium binding processes. (See Chapter 12 (p. 266) for discussions of equilibrium binding.)... Figure 14.13 The kinetic sequence of reactions that control the cyclic AMP concentration, and its binding to the effector system, and the kinetic sequence that controls the concentration of a neurotransmitter and its binding to the receptor on the postsyn-aptic membrane. Processes (1) are reactions catalysed by adenyl cyclase, and exocytosis. Reactions (2) are catalysed by phosphodiesterase and, for example, acetylcholinesterase. Reactions (3) are the interactions between the messenger and the effector system both the latter are equilibrium binding processes. (See Chapter 12 (p. 266) for discussions of equilibrium binding.)...
Most biomacromolecular interactions (bindings) involve the formation of some types of noncovalent bond and some specific region of the macromolecule called the binding site. Determinations of equilibrium binding processes are mostly indirect in that either i) the fraction of all of the ligand molecules (generally labeled molecules are used) in the system that are bound or ii) the fraction of binding sites that are occupied, is measured. [Pg.290]

Ni < > Zn. This order is usually observed for equilibrium constants of binding processes and... [Pg.59]

The generally accepted process for metal ion-catalyzed reactions of the sort we consider here involves pre-equilibrium binding with the substrate, followed by a reaction of the complex as schematized in Equation (1). Whether the metal ion is free or complexed by ligands, or bears an associated lyate, or whether the substrate is neutral or anionic, these appear to be just the sort of processes one might expect to experience large rate accelerations in passing from water to a medium of reduced dielectric constant such as alcohols or other lower polarity solvents. [Pg.274]

A second use of this type of analysis has been presented by Stewart and Benkovic (1995). They showed that the observed rate accelerations for some 60 antibody-catalysed processes can be predicted from the ratio of equilibrium binding constants to the catalytic antibodies for the reaction substrate, Km, and for the TSA used to raise the antibody, Kt. In particular, this approach supports a rationalization of product selectivity shown by many antibody catalysts for disfavoured reactions (Section 6) and predictions of the extent of rate accelerations that may be ultimately achieved by abzymes. They also used the analysis to highlight some differences between mechanism of catalysis by enzymes and abzymes (Stewart and Benkovic, 1995). It is interesting to note that the data plotted (Fig. 17) show a high degree of scatter with a correlation coefficient for the linear fit of only 0.6 and with a slope of 0.46, very different from the theoretical slope of unity. Perhaps of greatest significance are the... [Pg.280]

The interaction of ACh with the Torpedo nAChR. The data shown compare the equilibrium binding parameters obtained from fluorescence studies using covalently attached fluorescent probes and those obtained from radiolabelled [ H]ACh binding studies or functional measurements of cation flux. These data support a model in which the Torpedo nAChR carries sites of different affinities for ACh. We have previously suggested that occupancy of the lower affinity sites leads to channel activation whereas the higher affinity sites may play a role in desensitization processes... [Pg.147]

The thermodynamic approach starts from a sequence of binding processes at equilibrium that define the corresponding equilibrium constants, after which the BI is obtained. [Pg.35]

Consider again, for simplicity, the case m = 3. The adsorbent molecule P can form one of the three complexes which we denote by Pj, Pj, and P3, respectively, while Pq denotes the empty adsorbent molecule. The three binding processes and the corresponding equilibrium constants are... [Pg.35]

The phenomenological approach developed mainly by Wyman, and used by Ackers et al., starts by defining all the binding constants as equilibrium constants for the binding process. Thus, is defined in terms of the standard free-energy change for the process, written symbolically as... [Pg.187]

The second generalization, developed mainly by Koshland, is based on the recognition that enzymes (like any protein) have a multitude of conformations at equilibrium. Since the ligand is likely to interact differently with the various conformations, one can expect a shift in the distribution of conformations induced by the binding process. This is the induced fit model. It states that the best fit (by either geometrical or by a complementary pattern) does not necessarily exist before... [Pg.255]

Thus, if we freeze-in the equilibrium at any point along the binding process and then continue the process of binding, the slope of the equilibrated curve will always be steeper than that of the frozen-in curve. [Pg.321]

The equilibrium dialysis experiment revealed that histidine-substituted salicylamide was selected as an RNA ligand. Subsequent binding analysis by UV titrations and Job plot revealed the histidine-substituted salicylamide Cu + complex bound the target RNA hairpin with an apparent dissociation constant of 150 nM. This binding constant likely reflects more complex binding processes than a simple 1 1 interaction, as the observed binding curve saturates well below the concentration of the histidine-substituted salicylamide, and thus the actual affinity of the complex for targeted RNA is probably lower. Importantly, however, titrations with the... [Pg.97]

Equilibrium constants for the binding process fLH.Al. PMULI rLH+BA-L (H+BA-JJLl,... [Pg.294]

Studies of the pyrene label on actin indicate that the ATP-induced dissociation of actin occurs via a three-step process (steps 1, 2, and c, Scheme 1 Millar and Geeves, 1983). Initial fast equilibrium binding of ATP (controlled by and probably diffusion limited) is followed by an isomerization that alters the environment of the pyrene label on actin. This isomerization is fast in myosin II and much slower for some non-muscle myosins (-500 s-1 for Dictyostelium myosin II Kurzawa et al., 1997 >1000 s-1 for rabbit skeletal myosin II, Geeves andjeffries, 1988 100 s-1 for myosin lb at 20°C Coluccio and Geeves, 1999) and is accompanied by a very rapid... [Pg.180]

Phosphonate ester 30 can also be considered as a mimic of the transition state for subsequent esterolysis and aminolysis of the 8-lactone. In fact, the antibody that promotes ring formation was shown to catalyze the stereoselective reaction between 29 and 1,4-phenylenediaminc.39 The kinetic mechanism of the bimolecular process involves random equilibrium binding of lactone and amine, and the observed turnover rate could be approximated from the measured difference between the binding of reactants and the TSA. Again, entropic factors are presumed largely responsible for the observed rate acceleration, with minimal contributions derived from specific catalytic groups at the active site. [Pg.93]

Fig. 1 Equilibrium between reactants (E + I) and noncovalent complex (E- I ) in a typical enzyme-inhibitor binding process... Fig. 1 Equilibrium between reactants (E + I) and noncovalent complex (E- I ) in a typical enzyme-inhibitor binding process...

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See also in sourсe #XX -- [ Pg.290 ]




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