L-glutamic acid is the world's largest bulk amino acid product that is widely used in the food, pharmaceutical and chemical industries. Using Corynebacterium glutamicum G01 as the starting strain, the fermentation by-product alanine content was firstly reduced by knocking out the gene encoding alanine aminotransferase (alaT), a major by-product related to alanine synthesis. Secondly, since the α-ketoglutarate node carbon flow plays an important role in glutamate synthesis, the ribosome-binding site (RBS) sequence optimization was used to reduce the activity of α-ketoglutarate dehydrogenase and enhance the glutamate anabolic flow. The endogenous conversion of α-ketoglutarate to glutamate was also enhanced by screening different glutamate dehydrogenase. Subsequently, the glutamate transporter was rationally desgined to improve the glutamate efflux capacity. Finally, the fermentation conditions of the strain constructed using the above strategy were optimized in 5 L fermenters by a gradient temperature increase combined with a batch replenishment strategy. The glutamic acid production reached (135.33±4.68) g/L, which was 41.2% higher than that of the original strain (96.53±2.32) g/L. The yield was 55.8%, which was 11.6% higher than that of the original strain (44.2%). The combined strategy improved the titer and the yield of glutamic acid, which provides a reference for the metabolic modification of glutamic acid producing strains.
Glutamic Acid ; Corynebacterium glutamicum/genetics* ; Ketoglutaric Acids ; Metabolic Engineering ; Alanine

We produced α-ketoglutaric acid (α-KG) from L-glutamic acid, using enzymatic transformation approach with L-glutamate oxidase (LGOX). First, wild strain Streptomyces sp. FMME066 was mutated with NTG, a genetically stable mutant Streptomyces sp. FMME067 was obtained. Under the optimal nutrition conditions with fructose 10 g/L, peptone 7.5 g/L, KH2PO4 1 g/L and CaCl2 0.05 g/L, the maximum LGOX activity reached 0.14 U/mL. The LGOX was stable to pH and temperature, and Mn2+ had a stimulating effect. Finally, after 24 h enzymatic conversion under the optimal conditions, the maximum titer of α-KG reached 38.1 g/L from 47 g/L L-glutamic acid. Enzymatic transformation by LGOX is a potential approach for α-KG production.
Amino Acid Oxidoreductases ; metabolism ; Fermentation ; Glutamic Acid ; metabolism ; Ketoglutaric Acids ; metabolism ; Streptomyces ; genetics ; metabolism

Pyroptosis ; Ketoglutaric Acids ; Gasdermins ; Intracellular Signaling Peptides and Proteins/metabolism* ; Caspases/metabolism* ; Inflammasomes/metabolism*

PURPOSE: alpha-Ketoglutarate (alphaKG), a Krebs cycle intermediate, is extensively used in the kidney as a fuel substrate and as a counter anion for organic acid secretion. It is known to be taken up by the proximal tubule cells via the brush-border as well as basolateral membranes. We explored biochemical characteristics of the brush-border and basolateral alphaKG transport systems in pars convoluta and pars recta of the proximal tubule, respectively. METHODS: Brush-border and basolateral membrane vesicles (BBMV and BLMV) were isolated from rabbit renal outer cortex and outer medulla by Percoll gradient centrifugation. Vesicular uptake of alphaKG was determined by rapid Millipore filtration method using alpha-14[C]KG as a substrate. RESULTS: Both BBMV and BLMV showed a Na-gradient dependent uphill transport of alphaKG. The systems in both membranes were similarly inhibited by Li and activated by Na (Hill coefficient of 1.4). Kinetic analyses indicated that the Na-alphaKG cotransporters in the BBMV had a lower substrate affinity as compared with those in the BLMV. The transport systems in BLMVs showed a similar Km but different Vmax between the outer cortex (Km: 34 uM, Vmax: 3.3 nmol/mg protein/10s) and outer medulla (Km: 37, Vmax: 1.8). On the other hand, the systems in BBMVs were different in both Km and Vmax between the outer cortex (Km: 194, Vmax: 3.3) and outer medulla (Km: 89, Vmax: 1.7). CONCLUSION: The findings suggest that both axial and apical to basolateral heterogeneity of the Na-alphaKG cotransport system in proximal tubules may be due to a physiological adaptation to efficiently utilize alphaKG in the kidney.
Adaptation, Physiological ; Biological Transport, Active ; Centrifugation ; Citric Acid Cycle ; Filtration ; Hand ; Ketoglutaric Acids ; Kidney Tubules ; Kidney* ; Membranes ; Population Characteristics ; Symporters

Silver nanoparticles (AgNPs) is known as one of the most valuable metal nanoparticles in antibacterial and anticancer application. AgNPs-resistant bacteria has been documented, but it is unclear whether cancer cells can also escape the anti-cancer effect of AgNPs. In this study, we aimed to investigate this phenomenon and its underlying mechanism. The antibacterial activity and cytotoxicity of AgNPs were measured in the presence of HeLa cell metabolites. The status of AgNPs in the system associated with metabolites were characterized by UV-Vis, Zetasizer Nano ZS, and transmission electron microscopy. Non-targeted metabolomics was used to reveal the metabolites components that bind with AgNPs. HeLa cells were injected intraperitoneally to establish the tumor-bearing mice model, and the stability of AgNPs in mice serum was analyzed. The results manifested that HeLa cell metabolites inhibited the anticancer and antibacterial effects of AgNPs in a dose-dependent manner by causing AgNPs aggregation. Effective metabolites that inhibited the biological activity of AgNPs were stable in 100 ℃, insoluble in chloroform, containing sulfur elements, and had a molecular weight less than 1 kDa in molecular weight. There were 115 compounds bound with AgNPs. In vitro experiments showed that AgNPs aggregation occurred only when the concentration of α-ketoglutarate (AKG) and glutathione (GSH) together reached a certain threshold. Interestingly, the concentration of AKG and GSH in HeLa cellular metabolites was 10 and 6 times higher than that in normal cervical epithelial cells, respectively, which explained why the threshold was reached. Furthermore, the stability of AgNPs in the serum of tumor-bearing mice decreased by 20% (P < 0.05) compared with the healthy mice. In conclusion, our study demonstrates that HeLa cells escaped the anti-cancer effect of AgNPs through the synergistic effect of AKG and GSH, suggesting the need to develop strategies to overcome this limitation.
Humans ; Animals ; Mice ; HeLa Cells ; Silver/pharmacology* ; Ketoglutaric Acids/pharmacology* ; Metal Nanoparticles ; Anti-Bacterial Agents/pharmacology* ; Glutathione ; Microbial Sensitivity Tests

For the purpose of revealing the mechanism of the reduction of yeasts ethanol production rate after entrance of post-log phase, we used microarray to study expression profiles of the yeast Saccharomyces cerevisiae during the transition from mid-log growth phase to post-log growth. The results demonstrate that the global pattern of gene expression is very stable during the mid-log phase. However, a dramatic metabolic remodeling was found when the yeast entries post-log phase, during which many of amino acid synthesis and metabolism related genes are up-regulated, moreover, ion transport, energy generation and storage related genes are also up regulated during this phase, while a large number of genes involved in transposition and DNA recombination are repressed. Central metabolic pathways also engage in metabolic remodeling, within which the genes involved in succinate and a-ketoglutarate synthesis pathways are up regulated, accordance with those of amino acid synthesis and metabolism. These results demonstrate that the increasing demand for amino acids in post-log phase lead to a metabolic transition into TCA cycle and glyoxylate cycle, which subsequently reduce the ethanol production rate. This suggests a global insight into the process of yeast ethanol fermentation.
Amino Acids ; biosynthesis ; Ethanol ; metabolism ; Gene Expression Profiling ; Gene Expression Regulation, Fungal ; Ketoglutaric Acids ; metabolism ; Oligonucleotide Array Sequence Analysis ; Saccharomyces cerevisiae ; genetics ; growth & development ; metabolism ; Succinic Acid ; metabolism

A large amount of alpha-ketoglutarate (alpha-KG) (6.8 g/L) was accumulated in flask culture when CaCO3 was used as a buffering agent in the production of pyruvate by multi-vitamin auxotrophic yeast Torulopsis glabrata CCTCC M202019. In a 5 L jar-fermentor, less alpha-KG (1.3 g/L) was produced when NaOH was used to adjust the pH, while more alpha-KG (11.5 g/L) detected when CaCO3 was used as the buffer. In the latter case, the molar carbon ratio of pyruvate to alpha-KG (C(PYR)/ CalphaKG) was similar to that obtained in flask culture, suggesting the accumulation of alpha-ketoglutarate was related to the addition of CaCO3. Furthermore, it was found that: (1) delaying the addition time of CaCO3 decreased the a-ketoglutarate formation but increased C(PYR)/ C(alphaKG); and (2) under vitamin limitation conditions increasing the concentration of CaCO3 led to an increased a-KG accumulation at the expenses of pyruvate. To study which ions in CaCO3 was responsible for the accumulation of alpha-KG, the effects of different pH buffers on the a-KG accumulation were studied. The level of alpha-KG was found to correlate with the levels of both Ca2+ and CO3(2-), with Ca2+ played a dominant role and CO3(2-) played a minor role. To find out which pathway was responsible for the accumulation of alpha-KG, the effects of biotin and thiamine on alpha-KG accumulation was investigated. The increase in biotin concentration led to an increase in alpha-KG accumulation and a decrease in C(PYR)/ C(alpha-KG), while the levels of alpha-KG and C(PYR)/C(alphaKG) were not affected by thiamine concentration. The activity of pyruvate carboxylase was increased as much as 40% when the medium was supplemented with Ca2+ . On the other hand, the activity of the pyruvate dehydrogenase complex was unaffected by the presence of Ca2+. To conclude, the higher level of a-KG was caused by higher activity of pyruvate carboxylase stimulated by Ca2+, with CO3(2-) served as the substrate of the reaction.
Biotechnology ; methods ; Calcium Carbonate ; pharmacology ; Candida glabrata ; drug effects ; metabolism ; Fermentation ; drug effects ; Ketoglutaric Acids ; metabolism ; Models, Biological ; Pyruvic Acid ; metabolism

Alpha-ketogluratate is one of the key intermediates in the TCA cycle, playing an important role in the connection of carbon and nitrogen metabolism. This article aims at stating recent research progress in the production of alpha-ketoglutarate by microbial fermentation. First, a large group of microbes have been screened to accumulate alpha-ketoglutarate including prokaryotes and eukaryotes. Second, physiological characterization of over-accumulation of alpha-ketoglutarate is caused by thiamine defect and nitrogen starvation. Third, the process of fermentation was controlled and optimized by the manipulation of pH, dissolved oxygen and cofactors. Fourth, many metabolic engineering strategies were also presented for alpha-ketoglutarate production focusing on regeneration of cofactor and manipulation of the pathway. Last, we discussed the limitation of current progress and proposed the future research needs for microbial production of alpha-ketoglutarate.
Bacteria ; growth & development ; metabolism ; Fermentation ; Fungi ; growth & development ; metabolism ; Industrial Microbiology ; methods ; Ketoglutaric Acids ; metabolism ; Metabolic Engineering ; Yarrowia ; growth & development ; metabolism

OBJECTIVETo investigate the effects of pre-treatment of alpha-ketoglutarate (alpha-KG) on cyanide-induced lethality and changes in various physiological parameters in rodents.

METHODSThe LD50 of potassium cyanide (KCN) given orally (po), intraperitoneally (ip), subcutaneously (sc) or intravenously (iv) was determined in male mice, in the presence or absence alpha-KG given po, ip or iv. alpha-KG was administered 10, 20 or 40 min prior to KCN at 0.50, 1.0 or 2.0 g/kg by po or ip route, and at 0.10, 0.20 or 0.40 g/kg by iv route. Protection index (PI) was calculated as the ratio of LD50 of KCN in the presence of alpha-KG (protected animals) and LD50 of KCN in the absence of alpha-KG (unprotected animals). In a separate experiment, several physiological variables viz. mean arterial pressure (MAP), heart rate (HR), respiratory rate (RR), neuromuscular transmission (NMT) and rectal temperature (RT) were measured in anesthetized female rats pre-treated (-10 min) with po (2.0 g/kg) or iv (0.125 g/kg) alpha-KG and then administered sub-lethal (0.75 LD50) or lethal (2.0, 4.0 or 8.0 LD50) doses of KCN (po).

RESULTSPI of 4.52, 6.40 and 7.60 at -10 min, 3.20, 5.40 and 6.40 at -20 min, and 1.40, 3.20 and 5.40 at -40 min of po administration with a-KG was observed for 0.50, 1.0 and 2.0 g/kg doses, respectively, against KCN given by po route. When KCN was given ip, a PI of 3.38, 4.79 and 5.70 was observed for 0.50, 1.0 and 2.0 g/kg alpha-KG given ip (-10 min), respectively. A lower PI of 3.37, 2.83 and 2.38 was observed when KCN given sc was challenged by 2.0 g/kg alpha-KG given ip at -10, -20 or -40 min, respectively. Similarly, a PI of 3.37, 2.83 and 2.0 was noted when KCN given sc was antagonized by 2.0 g/kg alpha-KG given po at -10, -20 or -40 min, respectively. No appreciable protection was observed when lower doses of alpha-KG (ip or po) challenged KCN given by sc route. Pre-treatment of iv or po administration of alpha-KG did not afford any protection against KCN given po or iv route. Oral treatment of 0.75 LD50 KCN caused significant decrease in MAP and HR after 15 min, RR after 30 min and NMT after 60 min. There was no effect on RT. No reduction in MAP, HR, RR and RT was observed when rats received 2.0 or 4.0 LD50 KCN after pre-treatment of alpha-KG (po; 2.0 g/kg). However, no protection was observed on NMT. Protective efficacy of alpha-KG was not observed on MAP, HR, RR, and NMT decreased by 8.0 LD50 KCN. Decrease in MAP and NMT caused by 2.0 LD50 KCN (po) was resolved by iv administration of alpha-KG.

CONCLUSIONSCyanide antagonism by alpha-KG is best exhibited when both alpha-KG and KCN are given by po route. The protective effect of a-KG on cyanide-induced changes in several physiological parameters also indicates a promising role of alpha-KG as an alternative cyanide antidote.

Administration, Oral ; Animals ; Antidotes ; administration & dosage ; Dose-Response Relationship, Drug ; Female ; Injections, Intraperitoneal ; Injections, Intravenous ; Injections, Subcutaneous ; Ketoglutaric Acids ; administration & dosage ; Lethal Dose 50 ; Male ; Mice ; Potassium Cyanide ; poisoning ; Rats ; Rats, Wistar

PURPOSE: A family of organic anion transporters (OAT) has been identified, and several isoforms have been reported. The regulatory mechanisms of OATs functions, however, still remain to be elucidated. The rat OAT1 contributes to move a number of negatively-charged organic compounds between cells and their extracellular milieu. Caveolin (Cav) also plays a role in membrane transport. To address this issue, we investigated the protein-protein interaction between rOAT1 and Cav-1. METHODS: The expressions of rOAT1 and Cav-1 (mRNA and protein) were evaluated using RT-PCR and Western blot analysis. The localization of rOAT1 and Cav-1 was determined in the caveolae-rich membrane fraction isolated by sucrose density gradient ultra-centrifugation. For the direct binding between the rOAT1 and Cav-1 proteins, the immuno-precipitation method and confocal microscopy were employed. To perform functional analysis, a Xenopus oocytes expression system with the antisense oligonucleotides (ODN) technique was used. RESULTS: The expressions of rOAT1 and Cav-1 were detected in the kidney. The caveolae-rich membranous fractions from the kidney contained both rOAT1 and Cav-1 in the same fractions. The immuno-precipitation experiments showed the formation of a complex between the rOAT1 and Cav-1. The confocal microscopy using primary cultured renal proximal epithelial cells also supported the co-localization of rOAT1 and Cav-1 at the plasma membrane. The uptake function of rOAT1, as assessed by using a Xenopus oocytes expression system, was inhibited by the Xenopus Cav-1 antisense ODN. CONCLUSION: rOAT1 co-localizes with caveolin-1 in the caveolae, and caveolin-1 plays an important role in regulating the function of rOAT1.
Animals ; Avena ; Blotting, Western ; Caveolae ; Caveolin 1 ; Cell Membrane ; Epithelial Cells ; Humans ; Ketoglutaric Acids ; Kidney ; Kidney Tubules, Proximal ; Membranes ; Microscopy, Confocal ; Oligonucleotides, Antisense ; Oocytes ; Organic Anion Transporters ; Protein Isoforms ; Proteins ; Rats ; Sucrose ; Xenopus