Assessment of the seminal fluid proteins of Drosophila mojavensis and Drosophila arizonae. Experiment was performed using SILAC, whereas D. arizonae males were labeled with L-lysine-2HCL, 4,4,5,5-D4 (Lys 4) and D. mojavensis males labeled with L-Lysine-13C6,15N2 (Lys 8) and mated to their respective conspecific females (unlabeled). Following copulation females were immediately frozen in liquid nitrogen and stored at -80 C until reproductive tracts were removed and placed in 50 mM ammonium bicarbonate.