PROACROSIN-ACROSOMAL MATRIX BINDING INTERACTIONS IN EJACULATED BOVINESPERMATOZOA

The mechanisms regulating hydrolase release during the mammalian sperm acrosome reaction are poorly understood. The present study demonstrat es that specific domains of the acrosomal matrix of bovine spermatozoa function to maintain a particulate proacrosin pool and to regulate pr oacrosin/acrosin release. In sonicated sperm suspensions, 50-60% of th e total proacrosin activity was sedimentable, and the amount of sedime ntable proacrosin activity remained unchanged over time. Serial centri fugation and resuspension experiments demonstrated that the particulat e proacrosin fraction resulted from an equilibrium binding of proacros in to a stable sperm structure. To identify the proacrosin-binding str ucture of the acrosome, a purified sperm head fraction was isolated on sucrose density gradients. The sperm heads were extracted with Triton X-100, and a homogeneous acrosomal subfraction, the matrix complex as sociated with the outer acrosomal membrane (OMC), was isolated on Perc oll density gradients. A centrifugation assay was then used to demonst rate that the OMC specifically binds proacrosin in a dose-dependent ma nner. These data demonstrate that the OMC represents a stable structur al component of the acrosome that maintains a particulate proacrosin p ool. We propose that the OMC regulates proacrosin release during the a crosome reaction and maintains elevated acrosin concentrations at the site of sperm-egg interaction.