Leucine, one of the branched-chain amino acids, and alpha-ketoisocaproic acid (KIC) can stimulate muscle protein gain (but norleucine has no effect). Check out the data below. If you can figure out what half those acronyms mean than you should join Mensa. Leucine and KIC; good stuff.
Study Summary:
The branched-chain amino acid, leucine, acts as a nutrient signal to stimulate protein synthesis in skeletal muscle of young pigs. However, the chemical structure responsible for this effect has not been identified. We have shown that the other branched-chain amino acids, isoleucine and valine, are not able to stimulate protein synthesis when raised in plasma to levels within the postprandial range. In this study, we evaluated the effect of leucine, alpha-ketoisocaproic acid (KIC), and norleucine infusion (0 or 400 mumolkg(-1)h(-1) for 60 min) on protein synthesis and activation of translation initiation factors in piglets. Infusion of leucine, KIC, and norleucine raised plasma levels of each compound compared with controls. KIC also increased (P < 0.01) and norleucine reduced (P < 0.02) plasma levels of leucine compared with controls. Administration of leucine and KIC resulted in greater (P < 0.006) phosphorylation of eukaryotic initiation factor (eIF) 4E binding protein-1 (4E-BP1) and eIF4G, lower (P < 0.04) abundance of the inactive 4E-BP1eIF4E complex, and greater (P < 0.05) active eIF4GeIF4E complex formation in skeletal muscle compared with controls. Protein synthesis in skeletal muscle was greater (P < 0.02) in leucine- and KIC-infused pigs than in those in the control group. Norleucine infusion did not affect muscle protein synthesis or translation initiation factor activation. In liver, neither protein synthesis nor activation of translation initiation factors was affected by treatment. These results suggest that the ability of leucine to act as a nutrient signal to stimulate skeletal muscle protein synthesis is specific for leucine and/or its metabolite, KIC.
Reference
J Nutr. 2010 Jun 9. [Epub ahead of print] Leucine and {alpha}-Ketoisocaproic Acid, but Not Norleucine, Stimulate Skeletal Muscle Protein Synthesis in Neonatal Pigs. Escobar J, Frank JW, Suryawan A, Nguyen HV, Van Horn CG, Hutson SM, Davis TA.
