Fig. 4.

Precursor [²H₈]valine relative isotope abundance assessed for sperm and seminal vesicle proteins. Throughout the 35-day labeling period, the precursor RIA was calculated from divaline peptides for two seminal vesicle proteins (SVS6 and PATE4) and urinary MUPs (to define the profile of maximally labeled, secreted proteins; a). For two proteins derived from the sperm fraction (ODFP2 and LDHC; b), the precursor RIA curves reflect appearance of labeled peptide in the sample rather than a delay in precursor pool enrichment (see text). An epididymal secreted protein LCN5 is included to define the behavior of a protein secreted from the epididymis into the sperm fraction. For clarity, the trend lines are for illustration only, and the kinetic constants obtained by nonlinear curve fitting are given in the text.