Re-examination of Dietary Amino Acid Sensing Reveals a GCN2-Independent Mechanism.
Bottom Line: Animals cannot synthesize nine essential amino acids (EAAs) and must therefore obtain them from food.In contrast to previous results, we find that mice cannot rapidly identify threonine- or leucine-deficient food in common feeding paradigms.These behaviors are independent of the proposed amino acid sensor GCN2, pointing to the existence of an undescribed mechanism for rapid sensing of dietary EAAs.
Affiliation: Department of Physiology, University of California, San Francisco, San Francisco, CA 94158, USA.Show MeSH
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Mentions: GCN2 is proposed to detect the amino acid content of food by sensing rapid, post-ingestive changes in the level of amino acids in the blood. We therefore next determined how the consumption of EAA-deficient food alters the EAA composition of the blood by feeding mice amino-acid-deficient diets and then collecting blood for amino acid analysis. Consumption of T-def, L-def, and K-def food resulted in a progressive decrease in the concentration of the deficient amino acid in the blood (Figure 2A). This decrease was significant compared to control after 3 hr but not after 1 hr of feeding (Figure 2A). By contrast, the concentrations of other amino acids remained near 100% of control values, except that the concentrations of isoleucine and valine increased during L-def consumption (Figure 2B). This rise in isoleucine and valine concentrations has been previously reported, although the mechanism is not fully understood (Clark et al., 1966; Harper et al., 1984). Thus, plasma imbalance of amino acids develops over several hours of eating an imbalanced diet, but the changes in the first hour are small.
Affiliation: Department of Physiology, University of California, San Francisco, San Francisco, CA 94158, USA.