TI - Regulation of protein synthesis by branched - chain amino acids . AB - Historically , amino acids have been viewed as precursors for protein synthesis as well as metabolic substrates . Recently , a new role for amino acids as regulators of mRNA translation has been identified . In this role , they modulate the phosphorylation state of proteins that represent important control points in translation initiation , including the translational repressor 4E-BP1 and the ribosomal protein S6 kinase S6K1 . When administered orally to fasted rats the branched - chain amino acids are particularly effective in stimulating translation initiation . Of the branched - chain amino acids , leucine is most potent . Interestingly , leucine administration stimulates global rates of protein synthesis in skeletal muscle but not in liver . However , in liver , branched - chain amino acids enhance the translation of a particular set of mRNAs typified by those encoding the ribosomal proteins and translation elongation factors , suggesting that branched - chain amino acids upregulate the capacity of the tissue to synthesize protein .