ELM4: Competition binding

Question 1

What is the gaddum equation?

Answer 1

Extends Hill-Langmuir to account for presence of a second competing ligand

Question 2

What are the two equilibrium dissociation constants that govern the gaddum equation?

Answer 2

KD and Ki

Question 3

How do you work out the expression for total receptor concentration?

Answer 3

1. Write out expression for maximal binding which is [R]+[DR]+[IR]
2. Substitute for R
3. Make [DR] the subject
4. Simplify

Question 4

What equation can the gaddum equation be transformed into?

Answer 4

The competition binding equation

Question 5

What is the long form of the competition binding equation useful for?

Answer 5

Calculating affinity of drugs

Question 6

What is the short from of the competition binding equation useful for?

Answer 6

Plotting data

Question 7

How can you find the affinity of something using competition binding data?

Answer 7

1. Draw line at 50% of control binding to find x
2. Gives us the log IC50
3. Antilog gives IC50

Question 8

What equation is used to work out Ki from IC50?

Answer 8

Cheng-Prusoff equation

Question 9

What is the relationship between KD Ki and affinity?

Answer 9

Inversely proportional

Question 10

What is the relationship between pKD pKi and affinity

Answer 10

Affinity increases as they increase