[diablo]

Hi,

got a prob to solve this :

The following data were obtained for the binding of PDC-109, a bovine seminal plasama protein, to DMPC

[PDC-109]_total 0,05  0,15  0,3  1,0 3,0 µM
RU                  500 750 950 1000 1150 (SPR response units)

Calculate the K_a for the association of PDC-109 to DMPC

Ok, i would do scatchardplot:

[Y-Axis] i would plot : RU/free = bound/free
[X-Axis] i would plot: RU = bound

and since slope = -1/K_d it should be K_a

but: how can i subtract SPR-units from [PDC-109]_total ?
       --> because [PDC-109]_total has got µM as unit... and
       SPR ?

Thx for any help

Greets Diablooo

[Yggdrasil]

In surface plasmon resonance assays, you are constantly flowing ligand over your DMPC substrate.  Therefore, you are replenishing any bound ligand so that the [PDC-109] that you apply to the SPR chip is the concentration of free ligand.

However, it is possible to estimate the amount of protein bound from the response units.  Biacore, a company that makes SPR devices, says that 1000RU ~ 1ng/mm².

[diablo]

Thx for your Answer !

If i don't have additional data ( like 1000RU ~ 1nq/mm²; btw what is q? or you mean g(ramm)?  , would this be right? :

[X-Axis]: RU/[PDC-109] (because bound/free)
[Y-Axis]: RU

and K_a would be slope.

[Yggdrasil]

Yes, ng means nanogram.

The rest of your work looks right.

[diablo]

Thx alot for your help !