Fractionation and subcellular localization of marker enzymes in rainbow trout liver

The subcellular fractionation of rainbow trout liver homogenates prepared in 0.25 M sucrose was investigated using marker enzymes to assess the homogeneity of the resulting fractions. In addition to the usual mitochondrial and microsomal fractions, an additional fraction was sedimented between 8000 g for 10 min and 13,300 g for 10 min. Of the four accepted hydrolytic “marker” enzymes for rat liver lysosomes, the high relative specific activity (R.S.A.) of acid phosphatase was indicative of enrichment in this fraction. The R.S.A. patterns of 5'-nucleotidase and alkaline phosphatase indicated that the plasma membranes of fish liver were sedimenting with “nuclear” and microsomal pellets. This latter fraction contained the highest percentage of the total glucose 6-phosphatase, benzopyrene hydroxylase and glucuronyl transferase assayed in the fish liver homogenate before fractionation. The R.S.A. of these same enzymes in the microsomal pellet indicated an enrichment in this fraction relative to other cellular fractions.