Scatchard plots systems

In another paper, Liu et al. (30) described the interaction of hbronectin with heparin as a model system. The two distinct binding constants in the nanomolar range were derived from Scatchard plots and found in good agreement with published data. The established ACE binding assay was then applied to the molecular interaction of a kedarcidin chromophore with apoprotein. Dissociation constants in the lower micromolar range were calcu-... 

A. Bordbar, A. Saboury, and A. Moosavi-Movahedi, Biochem. Educ. 24, 172-175 (1996). The Shapes of Scatchard Plots for Systems with Two Sets of Binding Sites. ... 

A Scatchard plot obtained for the interaction of M2 and "intact" con A, Figure 6, was found to be linear as would be expected for single component systems and a value of 1.9 x 105 M-1 was obtained for the association constant. Also, identical difference spectra were obtained when the concentration of ligand and protein were symmetrically interchanged. Both of these results demonstrate the homogeneous behavior of the "intact" con A with respect to M2. Interestingly, the "nicked" con A that was obtained... 

A straight line will only be obtained for a system with a single type of receptor site, represented by a single binding constant. However, for MIPs, this is not the case since a heterogeneous distribution of binding sites exists, so that a curved Scatchard plot should be expected and. Table 6.5 contains some binding constants for MIP systems. 

Numerous other protein-surfactant systems when subjected to Scatchard analysis give curves that extrapolate to a number of specific binding sites very close to the number of cationic amino acid residues in the protein. Furthermore, chemical modification of the cationic sites, e.g., in the case of lysyl residues by acetylation, shifts the Scatchard plots to give lower values of n [32], Despite these interesting observations, Scatchard analysis should be treated with a degree of caution it is not entirely clear why such a good correspondence between n and the number of cationic sites is obtained, since the binding sites must only approximate to independence and are certainly not chemically identical. 

Common titration plots use A as a convenient value for graphical interpretation of data. A direct plot or Langmuir isotherm is obtained as a plot of A versus [G] the concentration at which A = 0.5 is the dissociation constant for the system. A plot of A/[G] versus A is known as a Scatchard plot [100], and the slope of the line is equal to -VK. A plot of IIA versus 1/[G], also known as a double reciprocal plot or Benesi-Hildebrand plot gives directly from the magnitude of the slope of the line [101]. 

The binding curves and the scatchard plots for these systems are shown in Fig, 1, As can be seen in Fig, lA, the values of r p in both systems are at low Cp region, but slightly different at the high Cp region. In this figure, a discontinuity of the curves can be observed near Cp = 5 yM, This discontinuity can also be observed more explicitly near r = 0,05 in Fig, IB. 

The reciprocal (Eq. 3) and Scatchard (Eq. 4) plots cannot be applied to experimental data obtained from experiments with whole plasma as it is necessary to know the molecular weight and the amount of protein in the experimental system. However, Sandberg and co-workers (S3) and Rosenthal (R8) have proposed a Scatchard-type plot based on Eq. (5). 

In a system with slow kinetics, the Ag and Ab need to be preincubated before injection into the capillary (45,46). Fixed concentrations of Ag or Ab are then incubated with different concentrations of Ab or Ag. The quantity of free Ab or Ag can be determined by the peak area using a calibration plot. Scatchard analysis is made by plotting the total amount of Ab or Ag vs. bound Ab or Ag. For the intermediate kinetics system, separation conditions, such as applied voltage, length of the capillary, pH, and other factors, can be changed so that the system can be analyzed using one of the final experimental protocols. 

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