OCCURRENCE OF LOW-MOLECULAR-WEIGHT AND HIGH-MOLECULAR-WEIGHT SELENIUM-COMPOUNDS IN FISH

Muscle from four species of fish, plaice (Pleuronectes platessa), mackerel (Scomber scombrus), cod (Gadus morhua), and herring (Clupea harengus), was analyzed for selenium in intact tissue and soluble and insoluble fractions obtained by centrifugation at 850 x g and 100 000 x g. In cod and herring muscle, 74-81% of the selenium was found in the 850g pellet, and the rest was mainly in the 100 000 X g supernatant (14-24%). For plaice and mackerel, larger proportions were found in the latter fraction (29-60%). Gel chromatography of the soluble fraction was performed to study the occurrence of low- and high-molecular-weight forms of selenium. The 100 000g supernatant from plaice and mackerel contained a high proportion of low-molecular-weight selenium compounds but the pattern of different peaks was not the same in the two species. The 100 000g supernatant from cod contained mainly high-molecular-weight selenium compounds. Storage of cod or herring in the cold for one week did not significantly affect the proportion of low-molecular-weight selenocompounds. The results indicated that the distribution of low- and high-molecular-weight selenocompounds varied in different species of fresh fish and of fish obtained frozen.