Why do cells need to be washed in PBS before biotinylation? - (May/16/2011 )
I was following a procedure for detecting cell surface labeled proteins today in the lab and it required I wash the cells in PBS prior to adding sulfo-NHS-biotin to the tubes containing the cells first. Why is this? The lab manual mentioned that PBS is an isotonic buffer of salts, could it be something to do with charge?
Some insight would be lovely
As you mentioned you are using PBS just to wash the cells from cell culture medium. It has nothing do with the charge.
see this wikipedia page for the meaning of isotonic
Probably to get rid of the serum proteins in your cell culture medium.