Perinatal changes in amino acid metabolism of rat brain,especially alanine and glutamic acid

The changes in both the levels of some free amino acids and their metabolism in the rat brain during the first 24 hr of postnatal life were studied. The content of glutamic acid decreased for the first 2 hr; it remained at the lowest level for the next 4 hr, when it began to increase. The content of alanine decreased for the first 6 hr and approached the adult level. Oxygen consumption, glucose oxidation, and pyruvate formation in the cerebral slices of the 24-hr-old rats were as much as 150% of that of the 19-day-old fetus. The distribution profile of radioactivity incorporated into the cerebral amino acids from the subarachnoid-injected [U¹⁴C]glucose was also changed. In the 2- and 6-hr-old rats, 50% of the total radio-activity recovered in the free amino acids was in alanine. Its rate decreased to 30% in the 24-hr-old and was 2% in the adult, while the radioactivity incorporated into glutamic acid increased. Alanine aminotransferase activity started to increase at birth and had the highest level at 24 hr after birth. It then decreased and finally reached the same level as shown at birth. However, aspartate aminotransferase increased during the first 6 hr after birth and did not change until the end of the first day of life.     

Neuroexcitatory amino acids: 4-methylene glutamic acid derivatives

Summary A short synthesis of 4-methylene glutamic acid was achieved. Under thermal conditions the corresponding anhydride reacted with 2,3 dimethylbutadiene to afford the corresponding DIELS-ALDER adduct in good yield. L-4-methylene glutamic acid essentially acts on glutamate metabotropic receptors and is as potent as L-Glu in producing IPs.     

Decomposition in presence of nitrate of amino acids,especially tyrosine,during acid hydrolysis of plant material and standard amino acid solution

Summary Nitrate present in or added to ryegrass samples considerably decomposed tyrosine during hydrolysis. Addition of 30 mg stannous chloride to 250 mg ryegrass in 250 ml 6N HCl had only a small preventing effect, whereas 480 mg SnCl₂.2H₂O or 0.17 ml thioglycollic acid, entirely prevented decomposition. Other amino acids remained unaffected by nitrate. Additions of nitrate to standard amino acid solutions completely decomposed tyrosine. Other amino acids, except proline, progressively decomposed with increasing nitrate additions. Effects from stannous chloride and thioglycollic acid were the same as on ryegrass     

Rapid determination of amino acids in biological samples using a monolithic silica column

A high-performance liquid chromatography method in which fluorescence detection is used for the simultaneous determination of 21 amino acids is proposed. Amino acids were derivatized with 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F) and then separated on a monolithic silica column (MonoClad C18-HS, 150 mm × 3 mm i.d.). A mixture of 25 mM citrate buffer containing 25 mM sodium perchlorate (pH 5.5) and acetonitrile was used as the mobile phase. We found that the most significant factor in the separation was temperature, and a linear temperature gradient from 30 to 49°C was used to control the column temperature. The limits of detection and quantification for all amino acids ranged from 3.2 to 57.2 fmol and 10.8 to 191 fmol, respectively. The calibration curves for the NBD-amino acid had good linearity within the range of 40 fmol to 40 pmol when 6-aminocaproic acid was used as an internal standard. Using only conventional instruments, the 21 amino acids could be analyzed within 10 min. This method was found to be suitable for the quantification of the contents of amino acids in mouse plasma and adrenal gland samples.     

The selective conversion of glutamic acid in amino acid mixtures using glutamate decarboxylase—a means of separating amino acids for synthesizing biobased chemicals

Amino acids (AAs) derived from hydrolysis of protein rest streams are interesting feedstocks for the chemical industry due to their functionality. However, separation of AAs is required before they can be used for further applications. Electrodialysis may be applied to separate AAs, but its efficiency is limited when separating AAs with similar isoelectric points. To aid the separation, specific conversion of an AA to a useful product with different charge behavior to the remaining compounds is desired. Here the separation of L‐aspartic acid (Asp) and L‐glutamic acid (Glu) was studied. L‐Glutamate α‐decarboxylase (GAD, Type I, EC 4.1.1.15) was applied to specifically convert Glu into γ‐aminobutyric acid (GABA). GABA has a different charge behavior from Asp therefore allowing a potential separation by electrodialysis. Competitive inhibition and reduced operational stability caused by Asp could be eliminated by maintaining a sufficiently high concentration of Glu. Immobilization of GAD does not reduce the enzyme's initial activity. However, the operational stability was slightly reduced. An initial study on the reaction operating in a continuous mode was performed using a column reactor packed with immobilized GAD. As the reaction mixture was only passed once through the reactor, the conversion of Glu was lower than expected. To complete the conversion of Glu, the stream containing Asp and unreacted Glu might be recirculated back to the reactor after GABA has been removed. Overall, the reaction by GAD is specific to Glu and can be applied to aid the electrodialysis separation of Asp and Glu. © 2014 American Institute of Chemical Engineers Biotechnol. Prog., 30:681–688, 2014     

Extracellular branched-chain amino acids, especially valine, regulate maturation and function of monocyte-derived dendritic cells

The functions of dendritic cells (DCs) are impaired in patients with liver cirrhosis. It is well-known that cirrhotic patients show decreased levels of plasma branched-chain amino acids (BCAA). Although amino acids are associated with maintaining the cell structure and function in many organs, limited data are available regarding the role of amino acids including BCAA in the immune system. We aimed to investigate the roles of BCAA in the function of human monocyte-derived DCs (MoDC). CD14-positive monocytes (CD14 (+)) were isolated from PBMC from healthy volunteers and hepatitis C virus (HCV) cirrhotic patients. In medium deprived of BCAA or valine, monocytes were able to differentiate into immature, but not into mature, DCs and showed weak expression of CD83. The deprivation of leucine or isoleucine did not affect this process. The MoDC allostimulatory capacity was significantly decreased in medium deprived of BCAA or valine (p = 0.017, p = 0.012, Bonferroni's analysis, respectively). Annexin V(FITC)/propidium iodide staining showed that the DC yield and viability were not significantly different under any medium. Immunoblotting demonstrated that depletion of valine or leucine decreased phospho-S6 kinase expression. Valine increased dose-dependently the allostimulatory capacity and IL-12 production of MoDC from both healthy volunteers and HCV cirrhotic patients. An elevated extracellular concentration of valine could improve the DC function in cirrhotic patients. These data provide a rationale for nutrition therapy that could be beneficial to patients with cirrhosis.     

The utilization of alanine, glutamic acid, and serine as amino acid substrates for glycine N-acyltransferase

The conjugation of benzoyl-CoA with the aliphatic and acidic amino acids by glycine N-acyltransferase, as well as the amides of the latter group, was investigated. Bovine and human liver benzoyl-amino acid conjugation were investigated using electrospray ionization tandem mass spectrometry (ESI-MS-MS). Bovine glycine N-acyltransferase catalyzed conjugation of benzoyl-CoA with Gly (Km(Gly) = 6.2 mM), Asn (Km(Asn) = 129 mM), Gln (Km(Gln) = 353 mM), Ala (Km(Ala) = 1573 mM), Glu (Km(Glu) = 1148 mM) as well as Ser in a sequential mechanism. In the case of the human form, conjugation with Gly (Km(Gly) = 6.4 mM), Ala (Km(Ala) = 997 mM), and Glu was detected. The presence of these alternative conjugates did not inhibit bovine glycine N-acyltransferase activity significantly. Considering the relatively low levels at which these conjugates are formed, it is unlikely that they will have a significant contribution to acyl-amino acid conjugation under normal conditions in vivo. However, their cumulative contribution to acyl-amino acid conjugation under metabolic disease states may prove to have a useful contribution to detoxification of elevated acyl-CoAs.