Splenic protein synthesis in magnesium deficiency: mechanism of the inhibition

To investigate the basis for the depressed protein synthesis in vivo in magnesium deficient spleens, the activities of splenic subcellular fractions in polypeptide synthesis were studied in vitro. Splenic ribosomes from Mg deficient animals were normal structurally and functionally. In contrast, supernatant fractions from the deficient spleens had a reduced ability to incorporate labeled amino acids into protein, both in the presence of endogenous mRNA and in the presence of added polyuridylic acid. The specific defects observed in the Mg deficient supernatants were twofold: There was a modest reduction in the rate of acylation of tRNA and a more marked reduction in the activity of the elongation factors, EF-I and EF-II. The reduction in elongation factor activity was quantitatively sufficient to account for the inhibition of protein synthesis in vivo.