Extraction and partial characterization of egg envelope (chorion) transglutaminase of rainbow trout, Oncorhynchus mykiss: Properties for efficient chorion hardening

We examined transglutaminase (TGase) catalyzing the formation of crosslinks between proteins and participating in hardening of egg envelope (chorion) of the rainbow trout, Oncorhynchus mykiss. The TGase was found exclusively in the chorion of unfertilized egg. As the chorion TGase could be extracted with 143 mM NaCl-10 mM Tris . HCl (pH 7.2) from the chorion, we examined its properties using the extract as enzyme source. Activity of the chorion TGase was temperature-sensitive, Ca2+-requiring, and was inhibited by iodoacetamide or amine derivatives such as hydroxylamine, cadaverine, and spermidine. The highest peak of the activity was found at pH 6.0. When the extract ed TGase was added to TGase-free unhardened chorion, its natural substrate, the chorion proteins were polymerized. The polymerization was inhibited by the addition of monodansylcadaverine. These properties are nearly similar to those of chorion hardening previously reported (12,14). When the extracted TGase was previously dialyzed against 10 mM Tris . HCl (pH 7.2), the activity was found to be 3- to 4-fold higher than that in 143 mM NaCl-10 mM Tris . HCl (pH 7.2) and to bind tightly to chorion. The properties of the enzyme at such lower ionic strength stand for an efficient chorion hardening occurring under the natural condition. (C) 1997 Elsevier Science Inc.