It was previously shown that among fishes in the suborder Salmonoidei, chum salmon and rainbow trout which belong to Salmonidae possessed the skin Type I collagens with a subunit composition of α1α2α3, contrasted to the collagen with (α1)₂α2 of ayu which belongs to Plecoglossidae. In this study, soluble skin and/or muscle Type I collagens were isolated from seven fish species in Salmonoidei and characterized with respect to their subunit composition.
Chromatographic and electrophoretic analyses revealed the existence of α1α2α3 heterotrimers in the skin Type I collagens of three other salmonid fishes (Japanese char, masu salmon, and coho salmon) and their α3 chains were distinct in chromatographic behaviour on CM-cellulose from those of many other teleosts. The muscle Type I collagen of Japanese char, however, was composed virtually of an (α1)₂α2 heterotrimer, although the possible presence in trace amounts of an α1α2α3 heterotrimer could not be excluded; the same result was previously obtained for the muscle Type I collagen of chum salmon. These composite results indicated the tissue-specificexpression in salmonid fish of a Type I collagen α3 gene. On the other hand, the skin or muscle Type I collagens of several non-salmonid fishes (capelin, Japanese smelt, ayu, and icefish) were found to lack an α3 chain characteristic of many groups of teleosts and existed as (α1)₂α2 heterotrimers.