Abstract
Tryptophan has a unique role as a nutritional signaling molecule that regulates protein synthesis in mouse and rat liver. However, the mechanism underlying the stimulating actions of tryptophan on hepatic protein synthesis remains unclear. Proteomic and metabolomic analyses were performed to identify candidate proteins and metabolites likely to play a role in the stimulation of protein synthesis by tryptophan. Overnight-fasted rats were orally administered L-tryptophan and then sacrificed 1 or 3 h after administration. Four differentially expressed protein spots were detected in rat liver at 3 h after tryptophan administration, of which one was identified as an ornithine aminotransferase (OAT) precursor. OAT is the main catabolic enzyme for ornithine, and its expression was significantly decreased by tryptophan administration. The concentration of ornithine was increased in the liver at 3 h after tryptophan administration. Ornithine is a precursor for polyamine biosynthesis. Significantly increased concentrations of polyamines were found in the liver at 3 h after administration of tryptophan. Additionally, enhanced hepatic protein synthesis was demonstrated by oral administration of putrescine. We speculate that the increase in ornithine level through suppression of OAT expression by tryptophan administration may lead to accelerated polyamine synthesis, thereby promoting protein synthesis in the liver.
Highlights
Tryptophan (Trp) is an essential amino acid that cannot be synthesized in the body and must be supplied by the diet [1,2]
Of the metabolic pathways affected by Trp administration, we focused on polyamine metabolism because polyamines are believed to play important roles in protein synthesis processes
Sidransky et al have reported the stimulatory effect of Trp on hepatic protein synthesis
Summary
Tryptophan (Trp) is an essential amino acid that cannot be synthesized in the body and must be supplied by the diet [1,2]. The principal role of Trp is a constituent of proteins. Of the 20 amino acids that comprise proteins, Trp is present in the lowest proportion in both proteins and plasma [3]. Trp is relatively less available than the other amino acids and is thought to play a rate-limiting role during protein synthesis [1]. It has been reported that Trp has a unique role as a nutritional signaling molecule that regulates protein synthesis in mouse and rat liver, in addition to its importance as a constituent of protein. Sidransky et al demonstrated that a single tube feeding of
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
