Journal of the American College of Nutrition, Vol 5, Issue 2 107-120, Copyright © 1986 by American College of Nutrition
Intracellular amino acid levels as predictors of protein synthesis
J. Metcoff
Protein synthesis depends on a complete complement of precursor amino
acids, specific acetylating enzymes, tRNA, and so forth. It has been
related to metabolism of individual amino acids, eg, valine and leucine;
however, the relation of protein synthesis to the ambient concentrations of
amino acids in the intracellular and extracellular pools has not been
defined. Using the viable, isolated granulocyte (leukocyte) as an in vitro
cell model, protein synthesis (incorporation of 4,5-3H-leucine) has been
related to simultaneous amino acid concentrations in the cell and plasma by
multiple regression analysis. Fifty-five normal neonates and 30 normal
adults were studied. Protein synthesis was higher in the infants than in
the adults (3,527 vs 2,685 pmole/hr/mg DNA). The intracellular
concentrations of most amino acids were higher than their concentrations in
plasma, except for valine and citrulline, which were lower. The
"aminograms" in the two pools also were very different. Forty-four percent
of the variance (R2) in protein synthesis was accounted for by the
intracellular concentrations of leucine, glycine, alanine, and taurine in
neonates and 45% by a combination of threonine, valine, methionine, and
histidine in adults. The intracellular concentrations of each of these
predictor amino acids in adults were, in turn, related to different
combinations of the plasma concentrations of threonine, phenylalanine,
tryptophan, isoleucine, histidine, citrulline, ornithine, arginine, and
glycine. Thus, it is possible to identify sets of intracellular amino acids
that predict the level of protein synthesis and to delineate combinations
of plasma amino acids whose levels account for a significant portion of the
variance in the intracellular predictor amino acids in normal human infants
and adults.
