Distribution, crypticity, stability, and localization of α-L-fucosidase of mouse cauda epididymal sperm

Sperm-associated and semen-specific isoforms of α-L-fucosidase are thought to function in fertilization in numerous organisms. Here, we report the localization, distribution, crypticity, and stability of this enzyme in mouse cauda epididymal sperm and cauda fluid. Western analysis revealed that the sperm-associated α-L-fucosidase is present as two isoforms (Mr ∼49 and 56 kDa), whereas the cauda fluid α-L-fucosidase shows a single band at 50 kDa. α-L-Fucosidase activity was detected using the fluorogenic substrate 4-MU-FUC. Of the total α-L-fucosidase activity recovered in the cauda epididymal contents, 74% was found in the cell-free cauda fluid and about 7% was found in sperm cells. During capacitation or permeabilization, cryptic intracellular stores of soluble enzyme were released to the supernatant, while leaving bound enzyme concentrated within the small volume of sperm. Moreover, membrane-associated enzyme activity was still detectable in acrosome-reacted cells. Immunofluorescence studies support the presence of α-L-fucosidase (originally localizing at the acrosomal area) at the equatorial segment after the acrosome reaction. α-L-Fucosidase activity of both cauda fluid and sperm at 37°C, 5% CO(2) was relatively stable and detectable up to 72 hr. The stability and appearance of mouse sperm-associated α-L-fucosidase in the equatorial segment after the acrosome reaction suggest that α-L-fucosidase may be involved in sperm-egg interaction.