Relative quantification of proteins by exponentially modified protein abundance indices (emPAI). Relative quantification for enriched plasma membrane samples was done by spectral counting within the shotgun-based approaches for 935 proteins (supplemental table). emPAI values were compared with literature estimations of protein abundance and showed overall good correlation. The inset shows gene ontology–based subcellular classifications for groups from high to low emPAI-ranking proteins. Reaching low emPAI values, low abundant plasma membrane components are mixed with contaminants by other compartments.