Isolation and characterization of ovochymase, a chymotrypsin-like protease released during Xenopus laevis egg activation.

A chymotrypsin-like protease contained in the perivitelline space of unactivated Xenopus eggs is released during egg activation and appears to participate in vitelline envelope conversion. This 30-kDa protease, which we have termed ovochymase, was isolated from the exudate of activated eggs using a soy bean trypsin inhibitor-agarose affinity column. The column eluant contained only two proteins, the 30-kDa ovochymase plus a 78-kDa chymotrypsin-like proteolytic activity. The 78-kDa protease was not usually observed in fresh egg exudate samples and thus was activated during the purification process and may represent the proposed precursor of the 30-kDa protease. The 30- and 78-kDa proteases were separated by gel filtration HPLC or by SDS-PAGE. The N-terminal amino acid sequence of SDS-PAGE-isolated ovochymase was determined to be VVGGQQAAPR. This conserved amino acid sequence, plus active site specific inhibition and substrate specificity studies, places ovochymase in the serine protease I family of enzymes. A two-dimensional protease activity gel revealed that ovochymase is present as several isozymes with a wide range of pI's.