A great way to specifically isolate and quantify proteins in the cell surface membrane is to take advantage of the biotinylation technique. It consists of labeling cell surface proteins with a biotin reagent before lysing the cells, and isolating these tagged proteins by NeutrAvidin pull-down. Then, the samples are subjected to SDS-PAGE separation, transferred to PVDF membranes and probed with specific antibodies. Quantification of cell surface expression is accomplished by densitometric measurement of the bands corresponding to the protein of interest and subsequent normalization by a membrane protein (as control).