Code words f or equations, scheme, and plots in multiple equilibrium problems
During the course of the linkage section, you are exposed to a large number of “names”
associated with various chemical schemes, equations that emerge from them, and ways to plot
these equations. These can be very confusing the first time around. So here is a list of the various
names used in the course, and what, exactly, they refer to.
Langmuir
This is a code-word for two things – an equation and a binding-scheme. A “Langmuir binding
scheme” is the simplest kind of binding of a ligand (X) to a receptor (R) to form a complex (RX):
X + R => RX Langmuir binding scheme
If you solve this scheme for the fraction of the receptor in the ligand-bound form as a function of
free X, you get:
f(x) = Kx/(1+Kx) Langmuir equation
Adair
This is a code-word for a general multiple-site binding scheme and for the equation that emerges
from it. The scheme envisions a macromolecule with N sites at which a single ligand, X, can
bind. Each binding step (for the first ligand, the second ligand, etc) has its own equilibrium
constant:
K1 K2 KN
Po – PX1 — PX2 — ::::: PX(N-1) — PXN Adair binding scheme
This scheme leads to an equation for the average number of sites bound as a function of ligand
concentration:
Adair equation
