Quantification of Sulfotransferases 1A1 and 1A3/4 in Tissue Fractions and Cell Lines by Multiple Reaction Monitoring Mass Spectrometry

Background: Within the sulfotransferase (SULT) superfamily of metabolic enzymes, SULT1A1 and 1A3/4 isoforms are of particular interest, due to their abilities to catalyze the sulfation of phenolic endobiotics and xenobiotics. Although the difference in their substrate specificity is well documented, an isoform-specific quantification method is still not available. Objective: To detect and quantify SULT1A1 and 1A3/4 in S9 fractions and cell lines using targeted mass spectrometry-based proteomics. Method: Samples were tryptically digested, and signature peptides were quantified using liquid chromatography- multiple reaction monitoring mass spectrometry (LC-MRM/MS). Stable isotopelabeled (SIL) peptides were used as internal and calibration standards. SULT1A1 and SULT1A3/4 were quantified in various S9 fractions and cell line samples. Results: Intraday and interday variabilities were low for relative quantification in S9 and cell line matrices (<8%). Expression profiles were validated using Western blot analysis of S9 fractions and lentiviral transduced SULT1A-overexpressing cell lines. Conclusion: A reproducible method for simultaneous quantification of SULT1A1 and SULT1A3/4 in S9 fractions and cell line samples was established and validated.