cording to these results, we expected that free acrosin will appear during the storage. However, at the same time Western blot analyses indicated the presence of high molecular weight bands and lack of acrosin I and II bands in sperm extracts with NPGB. These results strongly suggest that the proacrosin/acrosin system was not activated during the storage; in other words during storage the proacrosin system remained intact. In our opinion, these results suggest that the storage of turkey semen does not induce the activation of the proacrosin system in spermatozoa but increases the susceptibility of this system to be activated during extraction without NPGB. Douard et al. [13] demonstrated that the total phospholipid content of spermatozoa, especially phos- phatidylcholine—a major spermatozoa phospholipid— decreased during storage. It can be postulated that changes in phospholipid during storage correspond to increased susceptibility of the proacrosin/acrosin sys- tem to be activated. Further studies are necessary to test this hypothesis.
A recent study demonstrated that avian spermatozoa lose their ability to undergo acrosome reaction during liquid storage [19]. One possible explanation suggested by the authors would be a disturbance, during storage, of the accessibility of enzymes and several signaling pathways needed for the accomplishment of the acro- some reaction [37]. In our study we found an increase in the susceptibility of proacrosin/acrosin system of stored spermatozoa to be activated during extraction. It was indicated that the proacrosin/acrosin system may play an important role in the zona pellucida (ZP)- induced acrosome reaction of human spermatozoa [38]. If this hypothesis is true for avian species, increase in the susceptibility of the proacrosin/acrosin system to be activated during extraction could reflect a decrease in the ability of turkey sperm to acrosome reaction. Fur- ther studies are necessary to understand the mechanism of proacrosin/acrosin involvement in the acrosome re- action of turkey sperm.