PHARM/PCS V5 · Procedure 14 Receptor Pharmacology
Dissociation Constant III: Perturbation Methods
Get the forward and reverse rate constants of a drug-receptor reaction, and the dissociation constant K, from relaxation times measured after a rapid perturbation.
What it computes
Determines the forward and reverse rate constants (k1, k2) and hence the dissociation constant K = k2/k1 for the drug-receptor reaction, using the chemical relaxation method. Enter agonist concentration [A] and the corresponding relaxation time constant τ. The procedure plots 1/τ vs. [A] and reports k1 (slope), k2 (intercept), and K, with confidence limits.
Inputs and outputs
You provide
- Agonist concentration and the matching relaxation time constant τ, one pair per line
- A confidence level
PHARM/PCS reports
- k1 from the slope and k2 from the intercept of 1/τ against [A]
- K = k2/k1
- Correlation, standard errors, and confidence limits on all three
- A plot of 1/τ against agonist concentration, with the fitted line
When to use it
When you can measure the kinetics of the drug-receptor reaction (the relaxation time after a rapid perturbation) and want the rate constants themselves, not just the equilibrium K. It's the kinetic route to affinity, complementing the equilibrium methods in Procedures 12 and 13.
Reading the results
The plot uses the same regression machinery as Procedure 5, so its diagnostics apply: check that the 1/τ vs. [A] points are linear. The intercept (k2) is often small and error-prone, which makes K = k2/k1 the least certain output, so lean on its confidence limits.
Full regression report
The procedure runs the same regression analysis as Procedure 5 and reports r, standard errors, and confidence limits on all three quantities, matching the 1986 computer report. The intercept k2 is often small and error-prone, which makes K the least certain of the three.
This page describes the procedure. Calculations run inside the licensed PHARM/PCS V5 application. PHARM/PCS is a trademark of MCS Scientific LLC.