A survey was made of the effectiveness of acid media and of twelve different enzyme preparations in dissolving the zona pellucida of the mouse egg. It was found necessary to lower the pH of the medium to nearly 4 in order to dissolve the zona pellucida. Purified papain, crude ficin and crude Streptomyces griseus protease (`pronase') were found to be effective enzymes for zona pellucida removal. A crude preparation of β-glucuronidase also dissolved the zona pellucida, but its activity was shown not to be due to its β-glucuronidase content.
A difference in response between fertilized and unfertilized eggs was noted with the crude β-glucuronidase preparation : it dissolved the zona pellucida of unfertilized eggs more rapidly than that of fertilized eggs. Purified elastase did not dissolve the zona pellucida of either group, but caused the zona pellucida of some unfertilized eggs to swell.
The following enzyme preparations had no apparent effect on the mouse zona pellucida: purified trypsin, α-chymotrypsin and carboxypeptidase, crude preparations of trypsin, pancreatic lipase, lecithinase D, β-1,4-glucosidase and lysozyme.