l12 - 20.110J / 2.772J / 5.601J Thermodynamics of...

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20.110/5.60 Fall 2005 Lecture #12 page 1 Equilibrium: Application to Drug Design Based on “Rational cytokine design for increased lifetime and enhanced potency using pH-activated histidine switching,” Sarkar, Lowenhaupt, Horan, Boone, Tidor, and Lauffenburger, Nature Biotechnology 20 , 908 (2002). The analysis for equilibrium that we have used for reactions involving breaking and making covalent bonds applies equally well to reactions such as those involved in ligand-receptor binding, where the ligand and receptor are proteins R + L = C where R is the receptor, L is the ligand, and C is the receptor-ligand complex. The interactions between these proteins typically involve multiple non-covalent interactions, including hydrogen bonds, hydrophobic interactions, and electrostatic interactions. The equilibrium constant and Gibbs free energy change for the reaction are related in the usual way =− ln o a GRT K where the equilibrium constant K a is called the association constant [ ] [] = C RL The standard state needed to characterize G is defined at a set of specific reference conditions (pH, salt concentration, etc….). By convention, the reverse process (the dissociation) is used to characterize the strength of ligand binding through the equilibrium constant K D , also called the dissociation constant 20.110J / 2.772J / 5.601J
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l12 - 20.110J / 2.772J / 5.601J Thermodynamics of...

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