Fig. 1.

Quantification of ALDH1A1, ALDH1A2, and ALDH1A3 from testicular tissue S10 fractions. ALDH1A concentrations were measured using a novel LC-MS/MS-based peptide quantification method. Recombinant protein was digested and two peptides (each with two m/z transitions) were chosen for each protein to measure ALDH1A1 (A), ALDH1A2 (B), and ALDH1A3 (C) using LC-MS/MS. The peptide used for quantification was normalized to a corresponding stable isotope-labeled peptide with a [¹³C₆¹⁵N₂]lysine or [¹³C₆¹⁵N₂]arginine (D). Each peptide was observed in all 18 men and representative chromatograms of detection of ALDH1A1 (E), ALDH1A2 (F), and ALDH1A3 (G) in human testis are shown. The expression levels of the three proteins in the human testes of nontransgendered men are shown in (H). All peaks displayed in the chromatograms are scaled to counts per second (CPS).