PROTEIN-TYROSINE PHOSPHORYLATION AND SIGNAL-TRANSDUCTION DURING CAPACITATION-ACROSOME REACTION AND ZONA-PELLUCIDA BINDING IN HUMAN SPERM

During capacitation and acrosome reaction of human sperm, 7-14 protein s are phosphorylated, and two of these proteins (95 acid 51 kD) are ph osphorylated at tyrosine resides. The sperm proteins that bind ZP3 in humans have molecular identities of 95, 63, 51 (FA-1 antigen), and 14- 18 kD, respectively. Three of these molecules, 95-, 51-, and 14-18-kD proteins, undergo tyrosine phosphorylation, and 51 kD (FA-1 antigen) a lso undergoes autophosphorylation. Many of the sperm proteins that par ticipate in ZP binding are also involved in capacitation/acrosome reac tion. These findings indicate a vital role of protein tyrosine phospho rylation and tyrosine receptor kinases in sperm capacitation, acrosome reaction, and ZP binding. Since tyrosine phosphorylation is the prima ry, or even exclusive, indication of signal transduction, it would app ear that a signal transduction pathway is involved in these processes. However, the exact mechanism requires further study.