On the Subunit Composition of Fish Tropomyosins

Abstract

Tropornyosins were prepared from the ordinary muscle of 25 different species of fish, and were analyzed by SDS-polyacrylamide gel electrophoresis to obtain the subunit composition.
Tropomyosins from 22 species of fish showed a single band on the SDS-polyacrylamide gels, whereas tropomyosins from 3 species classified among the Scombrina fishes showed double bands on the gels. These results suggest that the former tropornyosins were composed of two α-ehain subunits (αα type). while the latter tropornyosins contained both α- and .β-chain subunits (αα type). Dye elution analysis of coomassie brilliant blue-stained gels indicated that approximate molar ratio of α to β chain subunits was 1:1 for the αβ type fish tropomyosins, whereas the same ratio was 3:1 for the αβ type rabbit tropomyosin.
All the tropornyosins tested were found to confer the Ca²⁺-sensitivity on the Mg²⁺-ATPase activity of desensitized actomyosin in the presence of troponin. Both αα and αβ type tropo-myosins formed a complex (i.e. regulatory protein) with troponin, and were effective as the αβ type of rabbit tropomyosin in regulating the actin and myosin interaction.