Alterations in the protein-synthesis, -degradation and/or -secretion rates in hepatic subcellular fractions of selenium-deficient mice.

Single mouse livers were subfractionated by differential centrifugation and isopycnic centrifugation on sucrose or metrizamide gradients and separated into subcellular compartments. The fractionation procedure was highly reproducible and yielded essentially similar results in different preparations of livers from selenium-adequate (Se+) and selenium-deficient (Se-) mice that were fed on a Torula-yeast-based diet containing less than 10 parts per 10(9) of selenium for at least 16 weeks. Mice of both dietary groups were injected intraperitoneally with 370 kBq of L-[U-14C]leucine, and 48 h later 1.85 MBq of L-[4,5-3H]leucine was injected intraportally. After another 1 h, the livers were removed and subjected to subcellular fractionation. Incorporation of the 3H label into proteins of the subcellular fractions was taken as a measure of relative protein-synthesis rate. The ratio of the 3H to the 14C protein-bound label of the same fractions was used as an estimate of relative protein-degradation and/or -secretion rate. The results showed a statistically significant 180% increase in protein-synthesis rate in the endoplasmic reticulum and a 80% increase in relative protein-degradation and/or -secretion rate in the same compartment. A significant decrease in the 3H/14C ratio, by 40 and 30% respectively, was observed in the Golgi fraction and in liver homogenate. The observed changes suggest a highly regulated hepatic response to selenium deficiency.