Subcellular Changes in Protein Metabolism and Magnesium Content of the Pancreas in Rats Fed Two Levels of Dietary Protein and Magnesium

Abstract

Subcellular distribution of magnesium and incorporation of C-valine into proteins of the pancreas were investigated in rats fed 15 or 30% casein diets with 50 or 1,000 ppm magnesium for 10 days. To permit estimates of enzyme synthesis and secretion, rats in all treatment groups were killed in both the fed and fasted states 5, 45, and 120 minutes after injection of C-valine. Microsomal, zymogen, and supernatant fractions were further fractionated into acid-soluble (transportable) and acid-pre- cipitable portions. The niitochondrial and the nuclei and debris fractions were analyzed without further fractionation. Decreased specific activities were observed in the proteins of acid-soluble microsomal fractions, the acid-soluble supernatant fraction, and the total niitochondrial fraction of fasted magnesium-deficient rats 2 hours after injection of labeled valine. Magnesium contents of four of the subcellular fractions were not sig nificantly affected by dietary treatment. Only in the microsomal fraction from fasted and refed rats fed the high proteinâ€highmagnesium diet was the magnesium concentra tion expressed per gram pancreas significantly greater than that in other treatment groups. The difference was not significant when expressed as micrograms magnesium per milligram protein. Magnesium content ( micrograms magnesium per gram pancreas ) of the microsomal, zymogen, and supernatant fractions was generally lower in fasted than in fed rats. Differences in magnesium content and distribution of labeled proteins in fed and fasted animals are discussed in terms of secretion mechanisms. J. Nutr. 104: 1618-1629, 1974.