Scatchard plot and others Flashcards
Who developed the Scatchard plot?
George Scatchard, an American chemist
What is the scatchard plot?
It is a graphical method for binding assay analyses.
What are the uses of the Scatchard plot?
- To linearise binding assay graphs
- In LBAs, it is used to give estimates of Kd and receptor conc.
- For showing if the ligand binds to one kind of receptor
- Shows changes in Bmax or Kd values in cases of receptor down-regulation or desensitisation
For the scatchard plot, what is y and what is x?
y = [L]bound/[L]
x = [L]bound
What is the scatchard equation?
[L]bound/[L] = -1/Kd.[L]bound + [R]total/Kd
The slope of the scatchard plot is?
-1/Kd
In a binding assay, what is y and x?
y = [L]bound
x = [L]
The intercept on the y-axis of the scatchard plot is?
[R]total/Kd
The intercept on the x-axis of the scatchard plot is?
[R]total
[R]total is, at best, an estimate of the binding sites available and is a measure of receptor density. T or F?
True
[R]total can also be called?
Bmax
If the ligand bind to multiple receptors, the graph is?
Curved
Bmax is?
The number of specific binding sites for the ligand in the assay
[L]bound = [R.L]. t OR f?
True
[R] = [R]total - [L]bound. T or F?
True
If the ligand bind to one receptor, the graph is?
Straight line
What is the difference between the scatchard plot for decensitisation and down-regulation.
In downregulation, there is an decrease in [L]bound/[L] as well as Bmax while in desensitisation, there is no decrease in Bmax but there is in [L]bound/[L]
How may errors arise in the scatchard plot?
- Experimental errors in the assay
- Heterogenity of receptors ligands can bind to
What is the Michelis-Menten’s equation for enzyme substrate interaction?
Bound = Bmax x [Radioligand]/ Kd x [Radio ligand]
The Michelis-Menten’s equation for enzyme substrate interaction is similar to what equation?
Equilibrium binding isotherm or Langmuir isothem
What is IC50?
The conc. of the unknown that displaces half the maximum bound radiolabeled ligand?
What is Ki?
The molar conc. of the competing ligand that would occupy 50% of the receptors when no radioligand is present.
IC50 can be calculated once the Ki is determined. T or F?
False.
Ki can be calculated once the IC50 is determined.
What is the Cheng-Prussof equation for ligand-receptor interactions?
Ki = IC50/ 1 + ([L]/Kd)
What is the Cheng-Prussof equation for enzyme-substrate interactions?
Ki = IC50/ 1 + ([S]/Km)
The lower the IC50 or Ki, the higher the affinity of the unknown/displacer for the receptor in question. T or F?
True
When may Ki be equal to IC50?
When the displacement is non-competitive
Fractional occupancy = E/Emax. T or F?
True
Kd = EC50. T or F?
False. Kd is not ED50 but ED50 may be related to Kd
What is EC50?
The conc. of agonist that provokes a response halfway btw the baseline and max response
Potency of a drug is sometimes expressed using?
pEC50 OR pD2
What is pEC50?
-logEC50
