Compartmentation of free amino acids for protein synthesis in rat liver

Abstract

The concept that a general intracellular pool serves as the sole precursor of amino acids for protein biosynthesis has been vigorously debated in recent years. To help resolve this controversy, we followed the distribution of intraperitoneally administered [(3)H]valine in the tRNA and the extracellular and intracellular compartments of rat liver. The specific radioactivity of the valine released from isolated tRNA was 2-3 times higher than that of intracellular valine, suggesting that the intracellular pool cannot be the sole precursor of amino acids used for charging tRNA. In addition, the specific radioactivity of the tRNA was only half that of the extracellular valine. Therefore it is unlikely that the valyl-tRNA is charged exclusively with amino acids derived from the extracellular pool. A model is proposed which stipulates that both extracellular and intracellular amino acids contribute to a restricted compartment that funnels amino acids towards protein biosynthesis.

Infusion of tumor necrosis factor/cachectin promotes muscle catabolism in the rat. A synergistic effect with interleukin 1.

“…4) represents a mixture ofintracellular and extracellular amino acids. Although the actual intracellular leucine specific activity may be estimated by subtracting the extracellular contribution, it has been shown that amino acyl-tRNA charging is affected by both intracellular and extracellular amino acid pool (35,36). Thus, the specific activity of free leucine in tissue homogenate, although not identical to that of leucyl-tRNA, is a better representative ofthe true precursor pool than intracellular leucine (37 ]leucine dilution may be defined in relationship to protein-bound uptake of the amino acid tracer.…”

Whole-body protein metabolism and plasma profiles of amino acids and hormones in growing barrows fed diets adequate or deficient in lysine

“…One further consideration with these kinetic approaches is that the PS estimated from leucine kinetics probably represents an underestimation of the actual PS values, because the IE of both leucine and KIC in the plasma pool may overestimate the IE of the true precursor pool, the amino-acyl tRNA (Airhart et al 1974). Intracellular leucine IE is often assumed to represent the best estimate of the IE of leucyltRNA.…”

Contents of nucleic and amino acids and rate of protein synthesis in developing flight muscles of Locusta migratoria

“…However, there do exist contradictory views about this, some considering the extracellular amino acid pool as the real precursor pool (Airhart et al, 1974;Van Venrooij et al, 1974), whereas others conclude that the total FAA pool provides precursors for protein synthesis (Fern & Garlick, 1974;Seglen & Solheim, 1978). In the locust flight muscle we have estimated the amount of protein synthesized at different times after [14C]leucine injection (Fig.…”