Subject: How to convert a concentration of an IFN γ of µg to units/ml?

I have an IFN-γ that has a Wight of 50µg . I need to 
convert this µg to units/ml. How can I calculate this conversion??. 
I would appreciate any help you could bring me.  
I have been looking in different places but i dont seem to be able to find the 
answer.I'll write also the discription which i become from the company.
Size:50µg
Biological activity:The ED50 is ≤ 0,05 ng/ml corresponding to a specific
activity of ≥ 2.0*10up7

Re: How to convert a concentration of an IFN γ of µg to units/ml?