Occurrence and properties of a thermostable protease secreted by sea-urchin embryos.

1. A trypsinogen-activating enzyme is distinct from the chorion-dissolving enzyme of the sea-urchin blastula, but is secreted with it. 2. This ;trypsinogenase' does not attack N-alpha-toluene-p-sulphonylarginine methyl ester, and is not inhibited by concentrations of di-isopropyl phosphorofluoridate or 7-amino-1-chloro-3-toluene-p-sulphonamidoheptan-2-one that are 98% effective against trypsin. It requires a small amount of Ca(2+) for activity, but is inhibited by more, from as little as 1mm. 3. Enzymic activity is associated with a wide range of particle weights, some apparently as high as 15x10(6). The mean particle weight can be decreased by sonication. 4. Fresh trypsinogenase in the higher range of particle weights appears to be remarkably stable to heating, e.g. retaining full activity after boiling for 15min.