Saturation binding

There should be specific, saturable binding to the receptor, accompanied by pharmacological characteristics appropriate to the functional effects, demonstrable using a radioactive, eg, tritium or iodine-125, ligand to label the receptor. Radioligand binding assays (1,6) have become a significant means by which to identify and characterize receptors and enzymes (see Immunoassays Radioactive tracers). Isolation of the receptor or expression of the receptor in another cell, eg, an oocyte can be used to confirm the existence of a discrete entity. 

Estimating the Bmax value is technically difficult since it basically is an exercise in estimating an effect at infinite drug concentration. Therefore, the accuracy of the estimate of Bmax is proportional to the maximal levels of radioligand that can be used in the experiment. The attainment of saturation binding can be deceiving when the ordinates are plotted on a linear scale, as they are in Figure 4.2. 

FIGURE 4.3 Erroneous estimation of maximal binding with Scatchard plots. The saturation binding curve shown to the left has no data points available to estimate the true Bmax. The Scatchard transformation to the right linearizes the existing points, allowing an estimate of the maximum to be made from the x-axis intercept. However, this intercept in no way estimates the true Bmax since there are no data to define this parameter. 

Saturation binding requires a traceable ligand but directly measures the interaction between a ligand and a receptor. 

Effect of excess receptor in binding experiments saturation binding curve (4.6.9)... 

Effect of Excess Receptor in Binding Experiments Saturation Binding Carve... 

Saturation binding, a biochemical procedure that quantifies the amount of traceable ligand (i.e., radioligand) to a receptor protein. It yields the affinity of the ligand and the maximal number of binding sites (i)max) see Chapter 4.2.1. 

Scatchard analysis, a common linear transformation of saturation binding data used prevalently before the widespread availability of nonlinear fitting software. The Scatchard transformation (see Chapter 4.2.1), while easy to perform, can be misleading and lead to errors. 

FIGURE 1. Scatchard plot of equilibrium-saturation binding of... 

In summary, the binding models first show a fraction of SB A or VML molecules that bind to Tn-PSM and jump between different aGalNAc residues of the mucin (Fig. 3A). As the number of bound lectin molecules increases, the affinity of the lectin decreases because of shorter diffusion distances on the mucin chain due to steric crowding and crosslinking by multiple bound lectin molecules (Fig. 3B and C). Finally, upon saturation binding, full lectin-mediated crosslinking of the complexes takes place (Fig. 3D). 

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