DISTRIBUTION OF METALS IN SUBCELLULAR FRACTIONS OF RAT LIVER

The localization of various metabolic processes of cells in particulate and soluble intracellular components has been studied intensively (l-3).The effect of added metals on these processes has also received attention (4-l3), but information on the metal content of the cell fractions is limited (14-16).The association of metals with proteins has been divided into two categories on the basis of their properties.Metalloproteins, wherein the metal is combined firmly with the protein, can be purified as stable, chemical entities ( 17).Metal-protein complexes, in which the metal is loosely bound, are subject to characterization only with difficulty.Any one metal in tissue may simultaneously be a component of one or more metalloproteins and metal-protein complexes, as well as being present in ionic form.The multiple role of metals has complicated the interpretation of analytical data from whole tissues.The investigation of metal content of subcellular fractions obtained by differential centrifugation (18-21) assists in further delineation of the problem.Reproducible and characteristic patterns of metal concentration, if demonstrated in any fraction, provide presumptive evidence for the functional significance of the metals found.In the present study, emission spectrogra,phy has been adapted to the simultaneous determination of several metals in fractions from livers of normal rats.It has been found that each metal is reproducibly distributed among the fractions, and that each fraction shows a characteristic and significantly different pattern of metal concentration. Methods Solutions and Apparatus-Precautionswere taken to prevent metallic contamination from solutions or apparatus.The 0.25 M sucrose was passed twice through a column of purified Dowex 50 cation exchange resin,