Acrosome Reaction

Courtesy of Chris Patton, Stanford University

Proteins (red) on the sperm plasma membrane come into contact with a polysaccharide in the egg jelly (yellow). This causes an influx of Ca++ into the sperm head and an increase in pHi. The Ca++ increase causes the acrosome vesicle (green) to fuse with the plasma membrane of the sperm and the vesicle undergoes exocytosis. The increase in pHi causes the actin (pink) to go from the globular state to the filamentous state pushing out the acrosomal process and exposing Bindin molecules (blue).