Subcellular fractionation of liver organelles from phenobarbital-treated rats by counter-current partition and sucrose gradient centrifugation.

Counter-current partition, sucrose density gradient centrifugation and enzymic analysis were used to explore the changes in rat liver organelles induced by phenobarbital. There was a small increase in partition coefficient and marker enzyme activity of the endoplasmic reticulum. The modal density of the marker enzyme showed a significant decrease reflecting the proliferation of the smooth endoplasmic reticulum. The mitochondria showed a bimodal distribution with a small reduction of marker enzyme activity. In contrast, lysosomes and peroxisomes were relatively unaffected by phenobarbital treatment. Phenobarbital caused a small but statistically insignificant increase in gamma-glutamyl transferase activity: density gradient centrifugation studies indicated that the increased activity was predominantly in the biliary canalicular elements. In contrast, cytosolic gamma-glutamyl hydrolase activity was strikingly reduced by phenobarbital treatment.