Fig. 7. Protein phosphorylation and dephosphorylation at serine (A) and threonine (B) residues in motility-feasible conditions. Sperm were diluted into either 50 mmol l^-1 NaCl + 5 mmol l^-1 CaCl₂ (lane b) or 300 mmol l^-1 NaCl + 10 mmol l^-1 CaCl₂ (lane c). Protein of dry sperm (lane a) was eluted after removal of seminal plasma by centrifugation. Sperm were motile in both the hypotonic solutions (50 mmol l^-1 NaCl) and the hypertonic solution (300 mmol l^-1 NaCl). Sperm were then collected and subjected to western blotting with (A) anti-phosphoserine antibody or (B) phosphothreonine antibody. Numbers on the left indicate molecular mass (kDa) obtained from molecular markers. Motility is shown below the lanes.