this was partly the result of removing the zona pellucida by trypsin digestion , since zona-free oocytes in the presence of trypsin inhibitor or zona pellucida-intact oocytes had half-lives of 99.1 +/- 15.2 and 120.5 +/- 17.4 minutes , respectively .
C0043519
zona pellucida
C0029045
oocytes