Biochemical and Biophysical Research Communications
Mechanisms responsible for regulation of branched-chain amino acid catabolism
Section snippets
Leucine has important effects above and beyond its role as an essential amino acid. Leucine signals an increase in protein synthesis
Animals cannot synthesize the BCAAs. The BCAAs are therefore essential amino acids and must be continuously supplied by the diet for growth and good health. A diet lacking just one of the essential amino acids will throw an animal into negative nitrogen balance and cause loss of body weight. Diets deficient in protein relative to energy likewise limit the supply of essential amino acids, restrict protein synthesis, and inhibit growth. Overall, the BCAAs are like other essential amino acids in
There is much evidence scattered throughout the literature suggesting that BCAAs and proper regulation of BCAA catabolism are important for growth and maintenance of body protein
Supplementation of the diet of pigs with carnitine reduces backfat thickness, decreases lipid deposition, and increases protein accretion [46]. Of great interest to the meat industry, this could also be an important finding for human nutrition. Carnitine is proposed, as would be expected, to bring about these effects by promoting fatty acid oxidation [46]. This in turn is pictured to induce greater anaplerosis by pyruvate carboxylase and reduced flux through BCKDC [46]. The consequence is
Medium-chain triglycerides and PPARα ligands promote the catabolism of BCAAs
In a nutshell, we believe that under certain conditions medium chain triglycerides and PPARα ligands can cause inhibition of BDK activity, which in turn increases BCKDC activity, and therefore lowers blood and tissue BCAA levels. The latter can decrease protein synthesis, either because BCAA levels are too low or the stimulatory effect of leucine on protein translation is lost. This may only be a problem when dietary protein levels are marginally adequate or restricted. The problem may go
Can BCAA be used to promote growth, improve muscle protein accretion, and help maintain body protein in various diseases and during ageing?
We believe that BCAAs have potential as therapeutic agents for the treatment of a number of medical conditions (liver failure, anorexia, cachexia, chronic inflammatory disease, and muscle wasting of ageing). Leucine is special among the BCAAs because of its ability to promote protein translation, decrease protein degradation, and promote insulin release. Valine and isoleucine do not have these effects but are nevertheless important since the proper ratios of the BCAAs must be maintained for the
Acknowledgements
This work was supported by grants from US Public Health Service (NIH DK 19259; R.A.H.), the Grace M. Showalter Residuary Trust (R.A.H.), and the Midwest American Heart Association (N.H.J.).
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