CHEM237 Lecture Notes - Lecture 12: Binding Constant, Durango, Dissociation Constant
13 Jun 2017
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Document Summary
A ligand binds to a protein at the binding site through non-covalent (non-reversible) bonds allowing for a reversible, transient equilibrium. Association equilibrium: ka = [pl]/[p][l] where large ka = tight binding < 0. 1nm (dgo <0, pl>p+l), on = how fast l finds p. Dissociation equilibrium: kd = 1/ka where large kd = loose binding > 10um (dgo >0, p+l >pl), off = how fast they detach. The [l] where half the binding sites are occupied. Y = [l] / [l] + kd. Binding curves: fraction of bound sites depends on [free l] and kd where l = known, independent (simple binding, no interaction between binding sites) Avidin and biotin: stable attractive complex due to very small kd. Enzyme substrate interactions are weaker since you want substrate: protein product (too tightly bound = inhibitor) As p+l pl, entropy of system decreases and entropy of surroundings increases (is binding thermodynamically favourable) Small on rate, smaller off rate = large binding constant.
