Adsorption of oviductal fluid proteins by the bovine sperm membrane during in vitro capacitation

¹²⁵I‐labeled oviductal fluid (ODF) proteins and antiserum to ODF were used to determine whether ODF proteins associate with the sperm membrane during in vitro capacitation. Luteal and nonluteal pools of ODF were obtained from oviduct catheters during the estrous cycle. Washed sperm (50 × 10⁶ sperm/ml) were incubated up to 4 h in a protein‐free modified Tyrode's medium (MTM), or MTM supplemented with 40% ODF, or 0.5 ng ¹²⁵I‐labeled ODF proteins. Solubilized sperm membrane proteins and incubatin media containing ODF proteins were separated by gel electrophoresis. Membranes isolated from bovine sperm previously incubated with ODF, absorbed five ¹²⁵I‐proteins: A doublet at 85–95 kDa, and others at 24, 34, 53, and 66 kDa. The amount of 66 kDA ¹²⁵I‐protein associated with the sperm decreased during the incubation, whereas the amount of 85 to 95‐kDa protein did not. Western blot analyses also detected the presence of ODF proteins (53, 66, 85–95, and 116 kDa) in solubilized membranes from sperm incubated in ODF. The 85 to 95‐kDa protein in ODF decreased in ODF. The 85 to 95kDa protein in ODF decreased in apparent molecular weight by 5 kDa when associated with the sperm membrane. At 53 kDa ODF proteins which associated with sperm were transformed from two to three separate proteins. These studies indicate that the surface of sperm is modified by adsorption of ODF proteins ot the membrane during in vitro capacitation. (c) 1992 Wiley‐Liss, Inc.