Fig 1.

(A) Workflow for absolute protein quantification of extracellular proteins. Shortly, extracellular proteins present in the cell supernatant were bound on StrataClean resin together with a known amount of concentration standards (spiked-in). Then, bound proteins were electroeluted by SDS-PAGE and separated together with UPS2 standards for absolute quantification. Finally, in-gel digestion of proteins was performed prior to liquid chromatography-tandem mass spectrometry measurement. (B) Concentration factors calculated with the concentration standards in four biological replicates. (C) Calibration curve for UPS2 quantification standards.