Bovine epididymal sperm proacrosin-acrosin system: quantification and partial characterization

Area of Science:

• Reproductive biology and biochemistry
• Enzymology
• Spermatozoa function

Background:

• Acrosin, a trypsin-like serine proteinase, is crucial for fertilization.
• Proacrosin, the inactive precursor, converts to active acrosin before sperm penetrate the zona pellucida.
• The proacrosin-acrosin system in bovine epididymis requires further characterization.

Purpose of the Study:

• To quantify and partially characterize the proacrosin-acrosin system in bovine epididymal sperm.
• To investigate the activation kinetics and factors influencing proacrosin conversion in bull spermatozoa.

Main Methods:

• Analysis of unpurified acrosomal extracts from bovine caput and cauda epididymal sperm.
• Proacrosin activation assays using sigmoidal curve analysis.
• Time-course studies at pH 8.0 and 25°C to determine activation rates.
• Investigation of calcium's effect on proacrosin activation and acrosin activity.

Main Results:

• Proacrosin constitutes 80-90% of the protein in ejaculated, caput, and cauda epididymal sperm.
• Proacrosin activation followed a sigmoidal curve.
• Complete conversion to active acrosin occurred in 3-5 hours post-isolation from cauda and caput epididymis, respectively.
• Calcium inhibited proacrosin activation in a dose-dependent and reversible manner.
• Calcium stimulated the hydrolytic activity of acrosin.

Conclusions:

• The proacrosin-acrosin system is present in bull epididymal and ejaculated sperm.
• Epididymal maturation involves the conversion of proacrosin to acrosin.
• Calcium plays a dual role, inhibiting activation but stimulating activity of acrosin.