Apparent association constants

The palytoxin-anti-palytoxin reaction is unique in that its binding increases with increasing temperature (Figure 4). The apparent association constant of the palytoxin to anti-palytoxin was 4.9 x 10 M at 0 C and 1.1 x 10 M" at 35 C, suggesting that H2O must be displaced from some of palytoxin s epitopes before they can bind to their antibody combining sites. 

Antibiotic Type of complex Apparent association constant (M ) Stoichiometry... 

There are two components to consider in the interaction of a drug with a protein. One is the capacity of the protein for binding drug molecules and this is related to the number of binding sites (n). The other is the affinity, or strength of binding, which is usually expressed as an apparent association constant (fc). 

Two fmrther equations have been derived from Eq. (2), and these are frequently employed to plot experimental data in order to obtain an estimate of the number of binding sites (n) and the apparent association constant (fc). The reciprocal plot (K9) involves the following rearrangement of (2). 

Fio. 5. Effect of apparent association constant (k) on the distribution of four model drugs. After Martin (M9), reproduced by courtesy of Nature. 

The correlation between the apparent association constants, K. which are derived from the competitive rates on Pt and reductions by diimide indicates that structural changes in the alkene generally have parallel effects on these reactions, Fig. 2. Because the diimide reduction is essentially free of steric effects, this effect is liable to account for some of the differences which are observed in extended groups of compounds. The small range of individual reactivities on Pt, which are zero order in alkene, can be understood in that the variation in structure which increases the driving force towards... 

Three representative examples 62, 63, 64 from a library of 20 are shown below. Kass is the apparent association constant and is approximately equal to 1/JQ. 

The apparent association constant K"(2D=T) for human hemoglobin is given by... 

The average apparent association constant Ka value that was derived from a numerical simulation of the experimental data [24] was found to be similar to that found for inclusion of 1 - adamantanecarboxylate in (3 - CD [25], The values for Ka at 35, 45, and 55°C were also determined in order to estimate the thermodynamic parameters for inclusion complexation. Table 4.2 summarized the results. 

The dichotomy of CV behavior between strongly and weakly interacting anions had been rationalized in the seminal article by Echegoyen s and Kaifer s groups with the square Scheme 1 [61]. When the strength of the interaction between the anion and the reduced redox form (here ferrocenyl) is significant, a new wave appears, and the variation of ferrocenyl potential between the free and bound forms of Scheme 1 is related to the ratio of apparent association constants F e -F ound = A °(V) = 0.059 log (K+/K0) at 25 °C. ound corresponds to the addition of one equiv. anion per ferrocenyl branch or the stoichiometric amount determined from the break points, for instance in Fig. 1. 

The addition of [HS04] [N(n-Bu)4] to the dendrimer 2 provokes the shift of the initial wave that reaches 110 mV at saturation, which leads to an apparent association constant K(+) = (55 5) 103 L Mol The titration diagram shows an equivalence point at 0.75 equiv. [HS04] [N( -Bu)4] per Fe4-cluster branch, although saturation is obtained at 1 equiv. [HS04] [N( -Bu)4] per Fe4-cluster branch. In this case the interaction is of the weak type, loose and not selective. 

D-fructose, D-ribose, and maltose were without effect. Equilibrium-dialysis analysis147 revealed one binding site for lactose on the abrin molecule, with an apparent association constant of 8 X 103 M l. 

The BS I that had been 125I-labeled by a diazonium coupling technique626 was employed in a study of lectin-receptor density on the B erythrocyte.191 Scatchard analysis of the binding data demonstrated a variation in receptor density among type B individuals from 7.2 X 104 to 13.4 X 104 sites per erythrocyte.191 Likewise, apparent association-constants for lectin-cell interaction varied from 1.1 X 107 to 2.9 X 107 M ... 

Although only the ratio of apparent association constants is accessible in this way, measurement of K0 by ll NMR (using the shifting NH signal) can lead to K, as well. For instance, with 9-Fc, K = (2.2 0.2) X 105 in CH2C12. When the interaction between the ferrocenyl dendrimer and the anion is negligible, only a CV wave shift is observed. The value of K+, the... 

Fig. 8.7 The pressure dependence at 35 C of the apparent association constant (Kajpp = i/fo) of human butyrylcholinesterase with a derivative of m-aminophenyl-trimethylammonium entrapped in the gel matrix for ( ) electrophoresis carried out in a discontinuous water-buffer system, and (o), electrophoresis carried out in a discontinuous heavy-water-buffer system. (Reproduced from work by Masson and Balny. °)...

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