Identification of 5,5′-Dithio-bis-2-nitrobenzoic Acid (DTNB) and Alkali Light Chains of Piscine Myosin

Myosins were prepared from the ordinary muscles of 14 species of fish, and analyzed for light chain subunits by SDS-gel electrophoresis. DTNB light chain and two alkali light chains A, and A₂, in the order of increasing mobility, were dissociated from the myosin of each fish. Molecular weights of the myosin subunits were determined to be in the ranges 17,500–21,000 for DTNB light chains, 25,000–30,000 for A₁ and 13,500–22,500 for A₂ light chains, respectively. In each scombroid fish tested, the molecular weight of A₂ was clearly larger than that of DTNB light chain; the opposite result was found in several other fishes including carp and pufferfish. In the group of fishes such as sardine and horse mackerel, both light chains showed the same molecular weight. These results suggested that there is some correlation between the molecular weight of A₂ and the locomotory activity of fish. Quantitative analysis showed that piscine myosins contained approximately two moles each of DTNB and of alkali light chains per mole. However, the ratios of A₁/A₂ differed widely, from 0.1 (grunt) to 2.6 (requiem shark).