Acrosin

Acrosin is a serine protease enzyme (EC 3.4.21.10) found in the acrosome of spermatozoa. It is synthesized as an inactive zymogen called proacrosin and is activated by auto-proteolysis or by other proteases.

Acrosin plays a crucial role in fertilization. Specifically, it facilitates the penetration of the sperm through the zona pellucida, the outer glycoprotein layer surrounding the oocyte (egg). This process, known as the acrosome reaction, involves the release of acrosomal enzymes, including acrosin, which hydrolyze the zona pellucida, allowing the sperm to reach the oocyte membrane and initiate fertilization.

The activity of acrosin is calcium-dependent. It is inhibited by a variety of protease inhibitors, including those found in seminal plasma. The regulation of acrosin activity is essential for preventing premature acrosome reaction and ensuring successful fertilization. Dysfunction or deficiency of acrosin has been implicated in infertility.