CSC technology. Unstimulated and ATRA stimulated NB4 cells were cultured in light medium (LM) and heavy medium (HM), respectively. Equal cell numbers of unstimulated and ATRA stimulated NB4 cells were combined and cell surface proteins were biotinylated on living cells either by the Cys-Glyco-CSC/Glyco-CSC protocol or the Lys-CSC protocol. After membrane preparation and protein digestion, biotinylated peptides were isolated by streptavidin affinity chromatography. “Piggyback” peptides were bound via disulfide bridges to biotinylated peptides on streptavidin beads, because protein disulfide bridges had been protected during cell lysis and protein digestion. In the Cys-Glyco-CSC and Lys-CSC protocol, piggyback peptides were eluted from streptavidin beads by chemical reduction. In the Glyco-CSC protocol, peptides with N-glycosylation were enzymatically released from streptavidin beads by PNGase F. HL60 cells were processed analogously except for the Lys-CSC protein biotinylation (for details see “Lys-CSC”).