Studies on Glutamic Acid Decarboxylase

A total of 50 lactic acid bacteria (LAB) isolates from Iranian traditional dairy products (Motal and Lighvan cheeses, and artisanal yogurt) were screened for gamma-aminobutyric acid (GABA) production. Firstly, a rapid colorimetric test was performed to evaluate the glutamate decarboxylase (GAD) activity among the LAB isolates examined. Thin layer chromatography (TLC) was then performed on selected strains to identify isolates with high/moderate GABA producing capacity, and a GABase micro-titer plate assay was employed to quantify GABA. Finally, two Lactococcus (Lac.) lactis strains were selected for GABA production optimization via Response Surface Methodology (RSM) following Central Composite Design (CCD). Forty-one out of the 50 isolates showed GAD activity according to the colorimetric assay. Eight isolates displayed strong GAD activity, while nine showed no activity; low to moderate GAD activity was scored for all other isolates. GABA production was confirmed by TLC in all isolates with high GAD activity and in four selected among isoaltes with moderate activity. Among the Lactococcus strains tested, Lac. lactis 311 and Lac. lactis 491 were the strongest GABA producers with amounts of 3.3 and 1.26 mM, respectively. These two strains were subjected to GABA production optimization applying RSM and CCD on three key variables: Monosodium glutamate concentration (MSG) (between 25 and 150 mM), incubation temperature (between 25 and 37 °C), and pH (between 4.0 and 5.0). Optimal conditions for GABA production by Lac. lactis 311 and Lac. lactis 491 of temperature, pH and MSG concentration were, respectively, 35.4 and 30 °C, pH 4.5 and 4.6, and MSG concentration of 89 and 147.4 mM, respectively. Under the above conditions, the amount of GABA produced by Lac. lactis 311 and Lac. lactis 491 was 0.395 and 0.179 mg/mL, respectively. These strains and the optimal culture conditions determined in this study could be used for the biotechnological production of GABA or applied in food fermentations for the development of naturally GABA-enriched foods.

BackgroundSalt stress is a serious abiotic stress that caused crop growth inhibition and yield decline. Previous studies have reported on the the synthesis of gamma-aminobutyric acid (GABA) and its relationship with plant resistance under various abiotic stress. However, the relationship between exogenous GABA alleviating plant salt stress damage and ion flux, amino acid synthesis, and key enzyme expression remains largely unclear. We investigated plant growth, Na+ transportation and accumulation, reactive oxygen species (ROS) metabolism and evaluated the effect of GABA on amino acids, especially SlGADs gene expression and the endogenous GABA content of tomato (Solanum lycopersicum L.) seedlings treated with or without 5 mmol·L− 1 GABA under 175 mmol·L− 1 NaCl stress.ResultsExogenous application of GABA significantly reduced the salt damage index and increased plant height, chlorophyll content and the dry and fresh weights of tomato plants exposed to NaCl stress. GABA significantly reduced Na+ accumulation in leaves and roots by preventing Na+ influx in roots and transportation to leaves. The transcriptional expression of SlGAD1–3 genes were induced by NaCl stress especially with GABA application. Among them, SlGAD1 expression was the most sensitive and contributed the most to the increase in glutamate decarboxylase (GAD) activity induced by NaCl and GABA application; Exogenous GABA increased GAD activity and amino acid contents in tomato leaves compared with the levels under NaCl stress alone, especially the levels of endogenous GABA, proline, glutamate and eight other amino acids. These results indicated that SlGADs transcriptional expression played an important role in tomato plant resistance to NaCl stress with GABA application by enhancing GAD activity and amino acid contents. GABA significantly alleviated the active oxygen-related injury of leaves under NaCl stress by increasing the activities of antioxidant enzymes and decreasing the contents of active oxygen species and malondialdehyde.ConclusionExogenous GABA had a positive effect on the resistance of tomato seedlings to salt stress, which was closely associated with reducing Na+ flux from root to leaves, increasing amino acid content and strengthening antioxidant metabolism. Endogenous GABA content was induced by salt and exogenous GABA at both the transcriptional and metabolic levels.

The effect of glutamic acid analogs on the biosynthesis and catalytic activity of glutamic acid decarboxylase in Escherichia coli

Perinatal Δ9-Tetrahydrocannabinol Exposure Augmented the Magnitude of Motor Inhibition Caused by GABAB, but not GABAA, Receptor Agonists in Adult Rats

Glutamate and gamma-aminobutyric acid (GABA), act as excitatory and inhibitory neurotransmitters in CNS respectively. An increase in glutamate and a decrease in GABA concentration were observed in aged brain. However, the mechanism of these changes has not been very well elucidated. Glutamate decarboxylase (GAD) catalyzes the conversion of glutamate to GABA. Since the vitamin B6 is essential for the activities of GAD, this study was undertaken to investigate the effects of vitamin B6 administration on age related changes in rat brain. The animals were injected intraperitoneally with 1, 10 and 100 mg vitamin B6 /kg body weight /day for 30 days, and specific activity of GAD was assayed in the brain supernatant. The activity of the enzyme in aged rats was significantly lower as compared to that of young animals. Vitamin B6 induced activation of the brain enzyme in both ages, but the rate of the activation was markedly pronounced in aged animals. Significant activation rate of GAD by vitamin B6 in aged rat brain may be resulted from either lower availability of vitamin B6 in aged animals, or lower affinity of the enzyme for pyridoxal -5-phosphate, which is likely to be related to conformational changes of the enzyme during aging. It is suggested that vitamin B6 may restore the activity of the brain glutamate decarboxylase in aged rat.   Key words: Glutamate, gamma-aminobutyric acid, vitamin B6, aging, glutamate decarboxylase.

Because previous work showed that in the newborn brain, but not in the adult brain, glutamate decarboxylase (GAD) is notably susceptible to heat, we have studied the possible involvement of GAD inhibition in febrile convulsions and the related changes in gamma-aminobutyric acid (GABA) content. Rats of different ages were subjected to hyperthermia, and GAD activity was determined in brain homogenates by measuring the release of 14CO2 from labeled glutamate and by measuring the formation of GABA. The latter method gave considerably lower values than the former in the youngest rats, and was considered more reliable. With this method, we found a 37-48% inhibition of GAD activity in rat pups 2-5 days old, which showed febrile seizures at progressively higher body temperatures, whereas in 10- and 15-day-old animals, which did not show convulsions, GAD activity was not affected by hyperthermia. Whole-brain GABA levels, however, did not change at any age. In contrast to GAD, choline acetyltransferase and lactic dehydrogenase activities were not altered by hyperthermia at any of the ages studied. These results suggest that a decreased efficiency of the inhibitory neurotransmission mediated by GABA, consequent to the inhibition of GAD activity, may be a factor related to febrile convulsions.

Glutamic acid decarboxylase activity associated with cerebral blood vessels appears to be part of a specific cerebrovascular system involving gamma-aminobutyric acid. This activity was characterized kinetically and pharmacologically and compared with that in brain and several nonneuronal tissues. Formation of gamma-aminobutyric acid from [14C]glutamate was measured in a soluble extract of pia-arachnoid blood vessels isolated from bovine brain. The vascular activity was like brain glutamate decarboxylase in that it required pyridoxal phosphate, was completely inhibited by aminooxyacetic acid, and had a similar affinity for glutamate. Cerebrovascular decarboxylase activity differed, however, from brain decarboxylase in that it was less sensitive to sulfhydryl reagents, was stimulated by 3-mercaptopropionic and cysteic acids, and was competitively inhibited by cysteine sulfinic acid. The glutamate decarboxylase activity of the cerebral vessels was similar to that in renal cortex and mesenteric blood vessels in its responses to sulfhydryl reagents and 3-mercaptopropionic acid. These findings are consistent with previous suggestions of a nonneuronal form of the enzyme and offer the possibility that synthesis of gamma-aminobutyric acid in cerebral blood vessels can be manipulated independently from that in neuronal tissue.

Gamma-aminobutyric acid (GABA) is the principal inhibitory neurotransmitter in the central nervous system and provides beneficial effects for human and other animals health. To accumulate GABA, samples from two different naked oat cultivars, Baiyan II and Bayou I, were steeped and germinated in an incubator. The content of GABA and glutamic acid as well as the activity of the glutamate decarboxylase (GAD) in oats during steeping and germination were investigated with an amino acid automatic analyzer. Compared with raw groats, an increase in GABA content of oat groats during steeping and germination was continuously observed for two oat cultivars. The activity of GAD increased greatly at the end of steeping and the second stage of germination for Baiyan II and Bayou I, respectively. Glutamic acid content of treated oat groats was significantly lower than that in raw groats until the later period of germination. GABA was correlated (p<0.01) significantly and positively with the glutamic acid rather than GAD activity in the current study. The results indicates that steeping and germination process under highly controlled conditions can effectively accumulate the GABA in oat groats for Baiyan II and Bayou I, which would greatly facilitate production of nutraceuticals or food ingredients that enable consumers to gain greater access to the health benefits of oats. However, more assays need to be further performed with more oat cultivars.

The impact of red and blue light-emitting diodes (LEDs) irradiation on the sugar metabolism and γ-aminobutyric acid in postharvest table grapes stored at 4 °C for 21 days after harvest were explored. Grape clusters were exposed to red and blue light irradiation at the same intensity (500 lx). The findings revealed that red and blue light treatments enhanced total soluble solids (TSS) and total acidity (TA) content. Furthermore, red-light irradiation retained higher phenolic compound during storage than blue light and control. Red-light radiation sustained higher levels of phenolic biosynthesis-related enzymes, including phenylalanine ammonia-lyase (PAL), tyrosine ammonia-lyase (TAL), cinnamate 4-hydroxylase (C4H), and p-coumarate ligase (4CL), than blue light irradiation and control. The results showed that red light increased glucose, fructose, and sucrose levels, which were 32.19, 33.18, and 2.95 mg g−1, compared with those in blue light and control at the end of storage and enhancing the sucrose synthase synthesis (SS-synthesis) and acid invertase (AI), while blue light enhanced sucrose synthase cleavage (SS-cleavage). In addition, red light irradiation increased glutamic acid decarboxylase (GAD) activity while red and blue light irradiation inhibited γ-aminobutyric acid transaminase (GABA-T) activity by 22.14 and 20.71 U g−1 at 21 days of storage, compared to control, leading to γ-aminobutyric acid (GABA) accumulation. These findings suggest that red and blue light will help in maintaining the quality of grape during postharvest storage.

Effects of components in culture medium on glutamate decarboxylase activity and γ-aminobutyric acid accumulation in foxtail millet (Setaria italica L.) during germination

Possible role of prolactin in the modification of medial basal hypothalamic glutamic acid decarboxylase activity

As compared with the nerve tissue of mammals, that of insects is known to be particularly rich in acetylcholinesterase1 and in choline-acetylase2. On the other hand, nothing has been reported so far about the occurrence in insects of another enzyme which, in mammals, is characteristic of nerve tissue, namely, glutamic acid decarboxylase. Its reaction product, γ-aminobutyric acid, has been recently found in the free state in bee nerve tissue, in amounts of the same order, on the basis of fresh weight, as in mammalian nerve tissue (Carta, S., and Frontali, N., unpublished work).

Dual effects of slightly acidic electrolyzed water (SAEW) treatment on the accumulation of γ-aminobutyric acid (GABA) and rutin in germinated buckwheat

Transmitter synthesis and convulsant drugs: Effects of pyridoxal phosphate antagonists and allylglycine

Ultrastructural localization and semiquantitative analysis of glycoconjugates in the tectorial membrane