Ligands depletion

These values can be substituted into the original expression defining Kj. Here, no assumptions or simplifications regarding ligand depletion are made ... 

Goldstein, A., Barrett, R. W Ligand dissociation constants from competition binding assays errors associated with ligand depletion. Mol. Pharmacol. 1987, 13, 603-609. 

In the limiting case of (n/NAv)C - L0, we may neglect ligand depletion (or accumulation, for dissociation experiments) in the medium and instead assume that the ligand concentration remains constant at its initial value, L0. Equation (4) then simplifies to... 

When pcell is not negligible compared to 1, then one must go back to the beginning and modify Eq. (5) for simple receptor/ligand binding, using Eqs. (41) and (43) in place of the simple constants k and kr, respectively. When ligand depletion can be considered negligible, the appropriately altered form of Eq. (5) is... 

In the complex (QHg)Cr(CO)3, in contrast, the Cr(CO)3 fragment, as a good acceptor by virtue of its three CO ligands, depletes the electron density on the aromatic ring. This makes the bound suscep-... 

In case of high receptor concentration or high affinity of the labeled ligand for the receptor resulting in ligand depletion, the equation loses its validity since it is based on the assumption that the free and total labeled ligand concentrations are approximately equal [207]. 

There is sufficient biological binding material to yield a good signal-to-noise ratio but not too much so as to cause depletion of the tracer ligand. 

While the signal-to-noise ratio can be improved with increasing the amount of membrane used in binding studies, too much membrane can lead to depletion of radioligand with a concomitant introduction of errors in the estimates of ligand affinity. 

The equation for displacement of a radioligand [A ] by a nonradioactive ligand [B] can be rewritten in terms of one where it is not assumed that receptor binding does not deplete the amount of radioligand in the medium (no change in [A free]) ... 

Limitations. Of the three methods, polarization has the lowest signal-to-noise ratio, and is most limited in its ligand concentration range. It works best when a significant fraction of the ligand is bound to the receptor. For FLPEP and cells the practical range is 0.5 to 3 njy (X L R). This method works best when free L is substantially depleted by the binding process. 

X-ray absorption spectroscopy has been performed on the isolated Rieske protein from bovine heart mitochondrial bc complex 69) as well as on the Rieske-type cluster in Burkholderia cepacia phthalate dioxygenase (PDO) (72). The analysis performed by Powers et al. 69) was significantly hampered by the fact that the presence of two histidine ligands was not fully recognized therefore, only the results obtained with the dioxygenase where the mononuclear iron has been depleted will be considered here. Table VII gives a comparison of the distances obtained from the fit of the EXAFS spectra assuming an idealized Rieske model and of the distances in the crystal structures... 

In deriving Eq. (1.2), we have assumed that the concentration of A does not change as ligand receptor complexes are formed. In effect, the ligand is considered to be present in such excess that it is scarcely depleted by the combination of a little of it with the receptors, thus [A] can be regarded as constant. 

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