Translational Control of Protein Synthesis in Muscle and Liver of Growth Hormone-Treated Pigs (original) (raw)
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The regulation of protein synthesis in animal cells by serum factors
Biochemistry, 1976
We have investigated the regulation of protein synthesis in animal cells by serum factors. Withdrawal of serum from the medium of actively dividing Vero cells resulted in an immediate decline in the rate of peptide chain elongation . Assay of elongation factor I (EFI) activity in the post-ribosomal supernatant as well as that associated with the ribosomes revealed that serum deprivation resulted also in reduction in the activity of this factor. The decline in the activity of EFI after serum deprivation occurred to the same extent and at the same time as the decline in the in vivo rate of protein synthesis and the in vitro peptide synthetic capacity of cell-free
Biochemical Journal, 1972
1. Aspects of skeletal muscle protein synthesis in vitro were studied in young rats given a low-protein diet for up to 10 days and during re-feeding with an adequate diet. 2. Partially purified muscle transfer factors (transferases I and II), crude and purified (NH4Cl-washed) ribosomes and a pH5 enzyme fraction were prepared for this purpose. 3. A marked decrease in the capacity of crude ribosomes to carry out cell-free polypeptide synthesis occurred within 4 days of feeding the low-protein diet. 4. The capacity of salt-washed ribosomes to promote amino acid polymerization, in the presence of added transfer factors and aminoacyl-tRNA, was only slightly decreased by the dietary treatment. 5. However, the capacity of salt-washed ribosomes to bind 14C-labelled aminoacyl-tRNA was decreased by feeding the low-protein diet. 6. The capacity of the pH5 enzyme fraction to promote amino acid incorporation in a complete cell-free system was decreased within 2 days of feeding the low-protein di...
2000
The objective of the current study was to examine the role of the branched-chain amino acid (BCAA) leucine in the regulation of hepatic protein synthesis and ribosomal protein (rp) mRNA translation in vivo. Food-deprived (18 h) male rats (200 g) were orally administered saline (control) or 270 mg leucine, isoleucine or valine and killed 1 h later. Administration of any BCAA resulted in enhanced phosphorylation of eukaryotic initiation factor (eIF) 4E-binding protein-1 (4E-BP1) compared with controls. However, leucine was the most effective at stimulating phosphorylation of 4E-BP1 as well as the 70-kDa ribosomal protein S6 kinase (S6K1). Despite these effects on components of the translation initiation process, there were no differences in total protein synthesis rates among treatment groups. The distribution of rp (S4, S8, L26) and non-rp (albumin, -actin) mRNAs across sucrose density gradients showed that the preponderance of hepatic rp mRNAs in control rats was unloaded from polysomes. Of the BCAA, only leucine was the most effective in causing a shift in the distribution of rp mRNA to polysomes compared with controls. Non-rp transcripts remained mainly polysome-associated under all conditions. These results suggest that leucine is most effective among the BCAA in its ability to stimulate translation of rp mRNA in liver. Furthermore, the translation of rp mRNA is disjointed from rates of total protein synthesis in liver and related to the degree of S6K1 phosphorylation. . 3 Abbreviations used: BCAA, branched-chain amino acids; Con, food-deprived rats; 4E-BP1, eIF4E-binding protein 1; eIF, eukaryotic initiation factor; Ile, food-deprived rats orally administered 270 mg isoleucine; Leu, food-deprived rats orally administered 270 mg leucine; rp, ribosomal protein; S6K1, 70-kDa ribosomal protein S6 kinase; TOP, terminal oligopyrimidine tract; Val, food-deprived rats orally administered 270 mg valine.
Experimental Cell Research, 1960
In viuo experiments have shown that the most active intracellular fraction for the incorporation of amino acids into proteins is the microsomal [3, 81. Similar observations have been reported from experiments on tissue homogenates [24], and a system for the in vitro incorporation of amino acids into proteins by isolated microsomes in the presence of cell sap has been described by Zamecnik and Keller [30]. Later on it was found that after treatment of the microsomes with DOC a particulate fraction was obtained which was characterized by a high RNA content. In amino acid incorporation experiments in uiuo, the proteins of this fraction became most rapidly labelled [ll 1. This fraction, called RNP-particles, was unable, however, to incorporate amino acids when tested in incorporation systems.