Practice question

Hardening of fertilization envelope after cortical granule release requires enzymatic cross-linking to provide mechanical strength. Granules release calcium-dependent enzymes including ovoperoxidase that utilizes hydrogen peroxide generated by calcium-dependent respiratory burst NADPH oxidase to form di-tyrosine covalent bonds between envelope proteins, and transglutaminase forming epsilon-gamma glutamyl-lysine cross-links, plus proteoliaisin remodeling vitelline structure. Calcium is required for activation and substrate binding of these enzymes. Result is tough, elevated envelope impermeable to sperm, providing permanent polyspermy block and protection from shear. Sodium, potassium, and magnesium ions alone do not drive hardening process.