Fig. 5.

Transamination of [²H₈]valine to [²H₇]valine during the labeling process. a, fully deuterated amino acids are also labeled at the α-carbon, and the deuterium atom at this position is metabolically labile as the amino acid undergoes reversible transamination through the cognate 2-oxo-acid. b, the shift in the labeled population was evident as a complex isotope labeling profile (as evidenced by a monovaline peptide FLQSEETVR from SVS4). The isotope profile was readily deconvoluted to reveal the extent of the transamination (see text). c, in sperm, based on LDH-C (open diamonds) and the outer dense fiber protein ODFP2 (filled diamonds), the extent of transamination was higher than for seminal vesicles as evidenced by SVS4 (open squares) and Kazal Inhibitor III (filled triangles).