Absolute quantification of human uridine-diphosphate glucuronosyl transferase (UGT) enzyme isoforms 1A1 and 1A6 by tandem LC-MS.

UGT enzymes catalyze the formation of glucuronic acid conjugates. Specifically selected representative stable isotope (C(13), N(15)) labeled peptide internal standards of each enzyme were employed to quantify UGTs 1A1 and 1A6 by LC-MS/MS using isotope dilution techniques. Inter day variability (n=5) for human liver microsomes was