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Ligand-Binding Kinetics
A receptor switches between unbound and bound states. At the single-molecule level this looks like stochastic binding and unbinding.
At the population level it becomes a smooth occupancy curve. Change ligand concentration, kon, and koff to connect molecular events to ensemble behavior.
kon[L]
1.00
KD = koff/kon
2.50
Predicted occupancy θeq
0.67
Measured occupancy
0.67
Relaxation time τ
0.67 s
Single Receptor and Occupancy Trace
Ensemble Occupancy
Binding Curve and Current Operating Point
Main ideas
For a single receptor, binding looks noisy and intermittent. For many receptors, the same process averages into a smooth occupancy curve.
The equilibrium occupancy is
\(\theta_{eq} = \frac{[L]}{[L] + K_D}\), where \(K_D = k_{off}/k_{on}\).
The approach to equilibrium happens on a timescale \(\tau \approx 1/(k_{on}[L] + k_{off})\).
For a single receptor, binding looks noisy and intermittent. For many receptors, the same process averages into a smooth occupancy curve.
The equilibrium occupancy is
\(\theta_{eq} = \frac{[L]}{[L] + K_D}\), where \(K_D = k_{off}/k_{on}\).
The approach to equilibrium happens on a timescale \(\tau \approx 1/(k_{on}[L] + k_{off})\).