[On the occurence of isopeptide bonds in the chorion of the rainbow trout (Salmo gairdneri Rich.) (author's transl)].

Chorions of unfertilized and fertilized eggs of the rainbow trout were isolated from tissue and yolk components and investigated for isopeptide bonds. The complete hydrolysis of the alpha-amide bonds was obtained by a system of four proteases. A chromatographic ion exchange system was used to separate Nepsilon-(beta-aspartyl)lysine as well as Nepsilon-(gamma-glutamyl)lysine from single amino acids. Chorions of unfertilized eggs contain neither Asp Lys nor Glu Lys bonds. Only chorions of fertilized eggs contain Glu Lys isopeptide. It is probably the high content of this isopeptide that is responsible for the greater mechanical stability of the fertilized teleostean egg chorion.