Acrosome Biogenesis in the Hamster: Ultrastructurally Distinct Matrix Regions Are Assembled from a Common Precursor Polypeptide(1)
The mammalian sperm acrosome is a membrane-bounded organelle containing several hydrolases that facilitate penetration of the egg investments . These enzymes are released to the extracellular environment during the acrosome reaction, a receptor-regulated exocytotic process involving fusion between the periacrosomal plasma membrane and the outer acrosomal membrane . Cell fractionation experiments have demonstrated a difference in the solubility properties of specific acrosomal proteins, and during the acrosome reaction specific hydrolases exhibit different temporal release patterns. cialis professional
For example, in guinea pig spermatozoa, dipeptidyl peptidase is rapidly released during the acrosome reaction, and this enzyme is sequestered to a specific domain along the dorsal surface of the acrosomal apical segment . In contrast, a considerable amount of proacrosin is associated with a particulate sperm fraction, and it is released more slowly during the acrosome reaction . This particulate nature and temporal release of different hydrolases may reflect a sequential requirement for specific hydrolases as sperm encounter different elements of the egg vestments during fertilization. The differences in solubility properties and release rates between acrosomal proteins appear to reflect their compartmentalization within the acrosome and their association with, or assembly into, stable acrosomal matrix assemblies.