The mode of action on the vitelline envelope of Xenopus hatching enzyme as studied by its two molecular forms

The medium in which dejellied prehatching Xenopus laevis embryos were cultured (hatching medium) can solubilize the vitelline envelope (VE) of dejellied eggs and dimethyl casein. Western blot analysis using antibodies against the hatching enzyme revealed the presence of 60 kDa and occasionally 40 kDa molecules in the hatching medium. ion-exchange chromatography or gel-filtration followed by enzyme activity assays indicated that the fractions containing 60 kDa molecules exhibit VE-solubilizing activity but: those containing 40 kDa alone do not, although both fractions exhibit the same level of proteolytic activity. However, solubilization of the VE was obtained when the 40 kDa fraction was mixed with an extremely low concentration of the 60 kDa fraction that cannot solubilize VE by itself, or when the 40 kDa fraction was applied to the VE that had been pretreated with a low concentration of the 60 kDa fraction. We propose that recognition and/or processing of the VE by 60 kDa molecules make solubilization of the VE possible by 40 kDa molecules.