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. 2016 Jul 1;15(9):2863–2876. doi: 10.1074/mcp.M115.057695

Fig. 3.

Fig. 3.

Identification and quantification of KLK4 in SP. A, Immunoenrichment-LC-MS/MS identification of peptide APCGQVGVPGVYTNLCK of the secreted isoform Q9Y5K2–1 of KLK4. B, Immunoenrichment-SRM identification of peptide FTEWIEK of the secreted isoform Q9Y5K2–1. C, Quantification of total KLK4 by ELISA and immunoenrichment-SRM assay in 22 SP samples. SRM assay measured peptide LDESVSESDTIR shared by secreted Q9Y5K2–1 and intracellular Q9Y5K2–2 isoforms. Ratio of intensities of secreted versus total KLK4 revealed the exclusive presence of the secreted isoform Q9Y5K2–1 in SP (see also supplemental Figs. S9–S11). Median CVs: 1.9% by immuno-SRM and 3.9% by ELISA; LOQs: 0.1 ng/ml by immuno-SRM and 0.03 ng/ml by ELISA.