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In addition to serving as the building blocks for protein synthesis, amino acids can be used as an energy source, through catabolism. The transamination, oxidative deamination, and decarboxylation processes that occur during amino acid catabolism are catalyzed by specific enzymes, including aspartate aminotransferase (AST), glutamate dehydrogenase (GDH), glutamic acid decarboxylase (GAD), and ornithine decarboxylase (ODC); however, the overall molecular mechanisms through which amino acid catabolism occurs remain largely unknown. To examine the role of mechanistic target of rapamycin complex 1 (mTORC1) on amino acid catabolism, mTORC1 was inactivated by rapamycin or shRNA targeting Raptor , versus activated by overexpressing Rheb or amino acids in human hepatocytes. The expression of amino acid catabolic genes and related transcription factor was investigated by RT/real-time PCR and western blot analysis. A few types of amino acid metabolite were examined by ELISA and HPLC analysis. The data showed that inactivated mTORC1 resulted in inhibition of NF- κ B and the expression of AST , GDH , GAD , and ODC , whereas activated mTORC1 enhanced NF- κ B activation and the expression levels of the catabolism-associated genes. Further, inhibition of NF- κ B reduced the expression levels of AST , GDH , GAD , and ODC . mTORC1 upregulated NF- κ B activation and the expression of AST and ODC in response to glutamate and ornithine treatments, whereas rapamycin inhibited the utilization of glutamate and ornithine in hepatocytes. Taken together, these results indicated that the mTORC1/NF- κ B axis modulates the rate of amino acid catabolism by regulating the expression of key catabolic enzymes in hepatocytes., Competing Interests: The authors declare no conflicts of interest., (Copyright © 2021 Meng Zhang et al.)

Scylla paramamosain is a kind of large euryhaline marine crab. As an important physicochemical parameter of seawater, salinity has a great impact on the survival, growth and quality of Scylla paramamosain. This research tested the content of non-volatile flavor substance, lactic acid and taurine on the 0, 1st, 3rd, 7th and 15th day in three salinity gradients (3, 13, 23) with HPLC (High-performance Liquid Chromatography) technology. Results have shown that in low salinity stress, the cumulative amount of free amino acids in muscle of Scylla paramamosain is more than that in hepatopancreas, while the cumulative amount of essential amino acids in hepatopancreas is more than that in muscle. In muscle, contents of three flavor amino acids are ranked as follows: sweet, bitter and delicious amino acid, and in hepatopancreas, it is bitter, sweet and delicious amino acid. The fluctuation rule of free amino acid, essential amino acid and lactic acid in Scylla paramamosain in the low salinity group is similar to that of other salinity control group, while the content of sweet amino acid, bitter amino acid, nucleotide, EUC, taurine is different from that of other salinity control groups. [ABSTRACT FROM AUTHOR]

The mud crab (Scylla paramamosain) is an important mariculture species, which has been successfully cultivated in inland saline-alkaline water of China. However, the study on the flavor quality of mud crab cultivated in inland saline-alkaline water has not been reported. The aim of this study was to investigate and compare the non-volatile flavor substances in the hepatopancreas and muscles of mud crabs cultured in inland saline-alkaline water (IS, 1.5 psu), coastal low salinity seawater(CS, 5 psu) and normal salinity seawater(NS, 13 psu). The results showed that there were no significant differences in total free amino acids (TAA) and essential amino acids (EAA) in muscle and hepatopancreas among the three groups. The contents of glycine (Gly) and alanine (Ala) in muscle and hepatopancreas in IS group were significantly higher than those in NS and CS groups. Taurine (Tau) content in IS-♂ group was significantly higher than that in NS-♂ group. The results of the principal component analysis showed that the similarity of amino acid composition and content in muscle and hepatopancreas of each population was related to the culture environment. To sum up, the mud crabs cultured in inland low saline-alkaline water can maintain the balance of total amino acid and essential amino acid content, the sweet flavor of edible parts was slightly enhanced, while the equivalent umami concentration was decreased. ● Inland saline-alkaline culture is a new way for the development of mud crab industry. ● Inland low saline-alkaline culture has an influence on the flavor of mud crabs. ● The contents of Gly and Ala in the muscle of saline-alkaline mud crabs are higher. ● The changes of free amino acids are related to osmoregulation. [ABSTRACT FROM AUTHOR]

• Low salt affects the nutrient composition of Eriocheir sinensis. • The increase of free amino acid content is related to organism metabolism. • The change of free nucleotide is related to the degradation pathway of ATP. • Lipid accumulation during development affects fatty acid composition. In this paper, the effects of temporary rearing time on the flavor substances of the edible parts of river crabs under the condition of 7 psu were determined based on high performance liquid chromatography (HPLC) and gas chromatograph (GC) techniques. The results showed that the content of free amino acids in the edible parts of river crabs could be increased under the condition of salinity of 7 psu. The content of organic acids in the edible part of Chinese mitten crabs was also affected by temporary culture under salinity 7 psu, and the change trend was the same as that of amino acids. The treatment of 7 psu can promote the accumulation of free nucleotides in the muscles, hepatopancreas and gonads of the crabs, and the equivalent umami concentration (EUC) values in the muscles and gonads of the crabs have been significantly increased. However, salinity 7 reduced the proportion of PUFA in muscles and gonads, resulting in a certain amount of nutrient loss. In summary, 15 days after treatment with salinity 7 can significantly improve the flavor of the edible parts of Chinese mitten crabs. [ABSTRACT FROM AUTHOR]