Effect of Magnesium Deficiency in Growing Rats on Synthesis of Liver Proteins and Serum Albumin

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Abstract
In vivo incorporation of L-14C-valine into serum albumin was significantly reduced in the livers of rats fed a 36% casein diet deficient in magnesium. Rate of disappearance of labeled albumin from the livers of deficient rats, however, was lower than that in pair-fed controls fed adequate magnesium. In vitro rate of incorporation of L-14C-valine by free and membrane-bound polysomes into total protein and serum albumin was consistently depressed in preparations from magnesium-deficient rats. No structural or functional changes were found in the polysomes. Most of the albumin synthesized in vitro was formed by membrane-bound polysomes and constituted 75% of the protein synthesized on this fraction. The change in protein synthetic capacity appeared to reside entirely in the supernatant fraction. There was a significant reduction in magnesium concentration of the supernatant fraction, but this was unlikely to have been the major cause of the change in rate of protein synthesis.