K =(Equilibrium)Dissociation constant(unit:M) Kd=k2/k1 K1 K3 R+D士RD→Effect K2 Low K=high affinity difficult to dissociate,nM to pM High K=low affinity quick to dissociate,mM to uM Kd is equal to the concentration of the agonist that makes 50% receptor bound with agonist.Kd = (Equilibrium) Dissociation constant (unit:M) Low Kd = high affinity = difficult to dissociate, nM to pM High Kd = low affinity = quick to dissociate, mM to M R + D RD Effect k1 k2 k3 Kd = k2/k1 Kd is equal to the concentration of the agonist that makes 50 % receptor bound with agonist