Sperm Glycosidases as Mediators of Sperm-Egg Binding in the Ascidians(Cell Biology)

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The activity of a-L-fucosidase was much higher than any other sperm glycosidases in Ciona intestinalis, where the terminal fucose residues of sperm receptors in the viteiline coat (VC) are known to play a key role in the sperm binding to the VC. On the other hand, β-D-N-acetylglucosaminidase was the highest in another ascidian, Phallusia mammillata, where D-N-acetylglucosamine has been suggested as the terminal sugar essential for the sperm binding. The optimal pH of Ciona α-L-fucosidase in situ was 3.9 and the activity in normal sea water was only 2% or less of the maximum. The binding of spermatozoa to the VC was remarkably inhibited by the synthetic substrates, pnitrophenyl α-L-fucoside and 4-methylumbelliferyl α-L-fucoside, and the competitive inhibitor of the enzyme, p-nitrophenyl β-L-fucoside, at millimolar concentrations. L-Fucose inhibited the binding only when the concentration was above 25 mM. Neither D-fucose nor p-nitrophenyl β-D-fucoside nor any other p-nitrophenyl glycosides were inhibitory at the concentrations thus far tested. The spermatozoa bound to the VC in normal sea water (pH 8.2) detached at 20℃ within 7 min of decreasing the pH to a value close to the optimum for the enzyme activity. At 0℃, however, the binding was maintained even after the pH was decreased. We suggest that the enzyme-substrate complexes formed between the α-L-fucosidase molecules at sperm surface and the sperm receptors in the VC are stable enough at the pH of normal sea water to allow the spermatozoa to bind to the VC.
社団法人日本動物学会の論文
1985-02-15

Sperm Glycosidases as Mediators of Sperm-Egg Binding in the Ascidians(Cell Biology)

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