Activation and subsequent degradation of proacrosin is mediated by zona pellucida glycoproteins, negatively charged polysaccharides, and DNA.

Boar proacrosin (E.C. 3.4.21.10, Mw 53 kD) was isolated by a modified method and subjected to autoactivation. Previously described molecular intermediates of 49 and 43 kD and a stable form (beta-acrosin, 35 kD) were identified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Autoactivation was expedited in the presence of either zona pellucida glycoproteins, fucoidan, or DNA. The end point of this accelerated conversion was the complete degradation of otherwise stable beta-acrosin via the formation of a characteristic active intermediate protein of 30 kD. All intermediate molecular forms observed during proacrosin activation/conversion exhibited the N-terminal sequence of the boar acrosin heavy chain, indicating a C-terminal processing mechanism. Hence zona pellucida glycoproteins stimulate proacrosin activation as well as acrosin degradation. Such a mechanism of proenzyme activation and degradation is to our knowledge described here for the first time and points to a previously unrecognized role of zona pellucida during gamete interaction.