Transfer ribonucleic acid charging in rat brain after consumption of amino acid-imbalanced diets

Recognition of an amino acid-imbalanced diet (IMB) is thought to occur in the anterior piriform cortex (APC) of the brain in response to a decrease in the limiting amino acid. We hypothesized that tRNA charging is decreased after ingestion of IMB and that this is part of the mechanism by which a decrease in the limiting amino acid is recognized. We investigated this question by determining levels of charged and uncharged tRNA using the periodate oxidation method and also by using high performance liquid chromatography (HPLC) analysis of amino acids acylated to brain tRNA. Using the periodate method, we found that isoleucyl-tRNA in both whole brain and APC of rats fed an isoleucine-IMB was increased, rather than decreased, in comparison to the basal diet and the corrected diet. Using HPLC analysis, we found that the absolute amount of tRNA charged with the limiting amino acid was not altered by dietary treatment. These two experimental approaches measure different aspects of tRNA charging, but the results clearly indicate that a reduction in tRNA charging is unlikely to be the signal by which a limiting amino acid is recognized in the brain 2 h after ingestion of IMB.