In order to elucidate the distribution and chemical forms of total mercury and selenium in the myofibrillar protein fraction, the ordinary muscle of marine fish was fractionated into subactomyosin and actomyosin at an ionic strength of μ=0.2 after being dissolved in 0.6M potassium chloride. The samples used were skipjack (Katsuwonus pelamis), Japanese sea bass (Lateolabrax japonicus) and red sea bream (Chrysophrys major).
For skipjack muscles, 50 to 70% of total mercury in the myofibrillar protein was found in the subactomyosin fraction. The total mercury contents in the actomyosin fraction of Japanese sea bass and red sea bream muscles were 70 to 75 and 85 to 90%, respectively, of those in the myofibrillar protein. Approximately 90% of selenium in the myofibrillar protein was found in the actomyosin fraction regardless of the fish species.
The concentration ratios of total mercury to selenium in the subactomyosin fraction of skipjack samples were 10-30 times those in the actomyosin fractions. However, the ratios of red sea bream samples showed no appreciable difference between the two protein fractions. The ratios of mercury to selenium concentrations in the subactomyosin fraction of skipjack samples containing high levels of mercury were far higher than 1:1 on a molecular basis.
The total mercury in the myofibrillar protein of skipjack samples was distributed approximately 50% in the native tropomyosin fraction from the actomyosin fractionated at ionic strength ranging from 0.05 to 0.6. Since the total nitrogen contents in the native tropomyosin fractions were about twice those in the subactomyosin fractions, subactomyosin seems to be a component of the native tropomyosin.