Effects of Dietary Copper Loading on Livers of Rats: I. Changes in Subcellular Acid Phosphatases and Detection of an Additional Acid p-Nitrophenylphosphatase in the Cellular Supernatant During Copper Loading

Significant changes occurred in lysosomal structure and function as copper was metabolized by rat livers. Hepatic total acid p-nitrophenylphosphatase (pNPase) activity was markedly increased in copper-loaded rats, and this increase was almost completely accounted for by heat- and formalin-stable (HFS) acid pNPase. Heat- and formalin-labile acid pNPase was essentially unchanged. On a subcellular level, the microsomal and supernatant fractions reflected the greatest relative increase in HFS acid pNPase. Increases in lysosomal, HFS acid pNPase in the large-granule fractions correlated with increase in solubilized large-granule enzymes, LG I, with mol wt > 200,000. LG II, representng solubilized large-granule enzymes with mol wt < 200,000, remained unchanged. Marked increases in supernatant acid pNPase were principally accounted for by a sevenfold increase in a supernatant lysosomal-like enzyme, DEAE Pk 1, separated by DEAE cellulose chromatography. An additional enzyme, DEAE Pk 2A′, that was hardly or not detectable in normal rats, was consistently demonstrated and increased in copper-loaded rats. Serum HFS acid pNPase increased in copper-loaded rats, suggesting that the increased hepatic supernatant acid pNPase in part escaped into the circulating fluid. Copper was principally associated with cytoplasmic organelles and was highest in mitochondrial and lysosomal fractions.