Separation of urinary proteins in BALB/c mouse urine by anion exchange chromatography. Urinary proteins from (A) adult male and (B) adult female BALB/c mice were separated by strong anion-exchange chromatography, monitored by ultraviolet (UV) absorbance (central trace, blue line). Five specific fractions corresponding to peak UV absorbance were collected from male urine, together with the corresponding fractions from female urine (I - V). The protein masses in each of these five fractions, along with the starting material (SM), were analysed by electrospray ionisation mass spectrometry (outer traces). Male fractions I and V contained male specific major urinary proteins (MUPs) that were not detectable in the female fractions. Resolution of each fraction on SDS-PAGE confirmed that male fraction V contained a very low abundance of the male-specific high mobility 18893Da MUP, darcin, which was not detectable in the female fraction. See Figure 1 for explanation of the molecular weight labelling on SDS-PAGE.