Thermodynamics of the GTP-GDP-operated Conformational Switch of Selenocysteine-specific Translation Factor SelB. Alena Paleskava, Andrey L. Konevega and Marina V. Rodnina . The Journal of Biological Chemistry, 287, 27906-27912 (2012). doi: 10.1074/jbc.M112.366120 .
d. Consider the following simple equilibrium for the interaction of a ligand L with a macromolecule M characterized by the dissociation constant Kd as shown below.
where M is the concentration of the free macromolecule, L is the concentration of free ligand, and ML is the concentration of complex. For dissociable binding interactions, Kd is as important as pka for a ionizable proton from an acid. An equation for ML as a function of Mo, L and Kd is shown above. Kd values are typically determined from binding experiment when Mo, the total amount of M is much less than free L. From the equation of ML above, draw a graph of ML vs L on the axes below.
An example is shown below with the Y axis being fractional saturation. The curve for ML vs L would be identical only it would plateau at a ML value = Mo, the total amount of macromoelcule present.
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