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91.
Most microorganisms can metabolize glycerol when external electron acceptors are available (i.e. under respiratory conditions). However, few can do so under fermentative conditions owing to the unique redox constraints imposed by the high degree of reduction of glycerol. Here, we utilize in silico analysis combined with in vivo genetic and biochemical approaches to investigate the fermentative metabolism of glycerol in Escherichia coli. We found that E. coli can achieve redox balance at alkaline pH by reducing protons to H2, complementing the previously reported role of 1,2-propanediol synthesis under acidic conditions. In this new redox balancing mode, H2 evolution is coupled to a respiratory glycerol dissimilation pathway composed of glycerol kinase (GK) and glycerol-3-phosphate (G3P) dehydrogenase (G3PDH). GK activates glycerol to G3P, which is further oxidized by G3PDH to generate reduced quinones that drive hydrogenase-dependent H2 evolution. Despite the importance of the GK-G3PDH route under alkaline conditions, we found that the NADH-generating glycerol dissimilation pathway via glycerol dehydrogenase (GldA) and phosphoenolpyruvate (PEP)-dependent dihydroxyacetone kinase (DHAK) was essential under both alkaline and acidic conditions. We assessed system-wide metabolic impacts of the constraints imposed by the PEP dependency of the GldA-DHAK route. This included the identification of enzymes and pathways that were not previously known to be involved in glycerol metabolisms such as PEP carboxykinase, PEP synthetase, multiple fructose-1,6-bisphosphatases and the fructose phosphate bypass. 相似文献
92.
Thermal performance of quartz capillaries for vitrification 总被引:1,自引:1,他引:0
In this paper we report the thermal behavior of a new approach for vitrification. Thermal performance of traditional open pulled straws is compared with a new technique based on the combined use of quartz capillaries with slush nitrogen. This new method of vitrification achieved ultrafast cooling rates of 250,000 °C/min. As a result, a much lower concentration of cryoprotectant was needed to reach vitrification. In fact, a cryoprotectant solution typically used in oocyte slow freezing protocols was shown to remain transparent after cooling to liquid nitrogen temperatures indicating apparent “vitrification”. This approach offers a new and very promising technique for vitrification of cells using low levels of cryoprotectants. 相似文献
93.
Glucose-6-phosphate as a probe for the glucosamine-6-phosphate N-acetyltransferase Michaelis complex
Glucosamine-6-phosphate N-acetyltransferase (GNA1) catalyses the N-acetylation of d-glucosamine-6-phosphate (GlcN-6P), using acetyl-CoA as an acetyl donor. The product GlcNAc-6P is an intermediate in the biosynthesis UDP-GlcNAc. GNA1 is part of the GCN5-related acetyl transferase family (GNATs), which employ a wide range of acceptor substrates. GNA1 has been genetically validated as an antifungal drug target. Detailed knowledge of the Michaelis complex and trajectory towards the transition state would facilitate rational design of inhibitors of GNA1 and other GNAT enzymes. Using the pseudo-substrate glucose-6-phosphate (Glc-6P) as a probe with GNA1 crystals, we have trapped the first GNAT (pseudo-)Michaelis complex, providing direct evidence for the nucleophilic attack of the substrate amine, and giving insight into the protonation of the thiolate leaving group. 相似文献
94.
Gene regulatory networks have been conserved during evolution. The Drosophila wing and the vertebrate hindbrain share the gene network involved in the establishment of the boundary between dorsal and ventral compartments in the wing and adjacent rhombomeres in the hindbrain. A positive feedback-loop between boundary and non-boundary cells and mediated by the activities of Notch and Wingless/Wnt-1 leads to the establishment of a Notch dependent organizer at the boundary. By means of a Systems Biology approach that combines mathematical modeling and both in silico and in vivo experiments in the Drosophila wing primordium, we modeled and tested this regulatory network and present evidence that a novel property, namely refractoriness to the Wingless signaling molecule, is required in boundary cells for the formation of a stable dorsal-ventral boundary. This new property has been validated in vivo, promotes mutually exclusive domains of Notch and Wingless activities and confers stability to the dorsal-ventral boundary. A robustness analysis of the regulatory network complements our results and ensures its biological plausibility. 相似文献
95.
96.
Raquel Rodríguez-Martínez Dolors Vaqué Irene Forn Ramon Massana 《Environmental microbiology》2022,24(5):2421-2434
Grazing controls bacterial abundances and composition in many ecosystems. In marine systems, heterotrophic flagellates (HFs) are important predators. Assemblages of HFs are primarily formed by species still uncultured; therefore, many aspects of their trophic behaviour are poorly known. Here, we assessed the functional response of the whole assemblage and of four taxa grown in an unamended seawater incubation. We used fluorescently labelled bacteria to create a prey gradient of two orders of magnitude in abundance and estimated ingestion rates. Natural HFs had a half-saturation constant of 6.7 × 105 prey ml−1, a value lower than that of cultured flagellates and within the range of marine planktonic bacterial abundances. Minorisa minuta was well adapted to low prey abundances and very efficient in ingesting bacteria. MAST-4 and MAST-7 were also well adapted to the typical marine abundances but less voracious. In contrast, Paraphysomonas imperforata, a typical cultured species, did not achieve ingestion rate saturation even at the highest prey concentration assayed. Our study, beside to set the basis for the fundamental differences between cultured and uncultured bacterial grazers, indicate that the examined predator taxa have different functional responses, suggesting that they occupy distinct ecological niches according to their grazing strategies and prey preferences. 相似文献
97.
Caicedo-Lopez Laura Helena Guevara-Gonzalez Ramon G. Ramirez-Jimenez Aurea K. Feregrino-Perez Ana A. Contreras-Medina Luis Miguel 《Phytochemistry Reviews》2022,21(6):1941-1968
Phytochemistry Reviews - Capsaicinoids (CAPs) are compounds synthesized and accumulated exclusively in pepper fruits. They are known as health-promoting compounds, and upbringing approaches to... 相似文献
98.
The chemokine IL-8 is known to be synthesized by glial cells in the brain. It has traditionally been shown to have an important role in neuroinflammation but recent evidence indicates that it may also be involved in rapid signaling in neurons. We investigated how IL-8 participates in rapid neuronal signaling by using a combination of whole-cell recording and single-cell RT-PCR on dissociated rat septal neurons. We show that IL-8 can acutely reduce Ca(2+) currents in septal neurons, an effect that was concentration-dependent, involved the closure of L- and N-type Ca(2+) channels, and the activation of G(ialpha1) and/or G(ialpha2) subtype(s) of G-proteins. Analysis of the mRNAs from the recorded neurons revealed that the latter were all cholinergic in nature. Moreover, we found that all cholinergic neurons that responded to IL-8, expressed mRNAs for either one or both IL-8 receptors CXCR1 and CXCR2. This is the first report of a chemokine that modulates ion channels in neurons via G-proteins, and the first demonstration that mRNAs for CXCR1 are expressed in the brain. Our results suggest that IL-8 release by glial cells in vivo may activate CXCR1 and CXCR2 receptors on cholinergic septal neurons and acutely modulate their excitability by closing calcium channels. 相似文献
99.
Pacini A Quattrone A Denegri M Fiorillo C Nediani C Ramon y Cajal S Nassi P 《The Journal of biological chemistry》1999,274(49):35107-35112
100.
PCR-based genomic fingerprinting by use of enterobacterial repetitive intergenic consensus primers (ERIC-PCR) was evaluated
for its use in fingerprinting DNA of mixed Gram-negative bacterial strains and BIOLOG Gram-negative (GN) microplate substrate
communities. ERIC-PCR fingerprints of six different pure bacterial strains and a combined mixture of the strains were compared
with fingerprints obtained by two more established methods: amplified ribosomal DNA restriction analysis (ARDRA) and random
amplified polymorphic DNA analysis (RAPD-PCR). The ERIC-PCR fingerprint of the mixed strains was highly reproducible and was
more species-specific and representative of the individual strain fingerprints than the ARDRA and RAPD-PCR fingerprints, respectively.
ERIC-PCR fingerprinting of model and rhizosphere BIOLOG GN substrate communities also provided clearly distinguishable fingerprints.
Results of this study suggest that ERIC-PCR represents a rapid and highly discriminating method for fingerprinting DNA of
mixed Gram-negative bacterial strains and BIOLOG GN substrate communities.
Received: 11 September 1998 / Accepted: 29 October 1998 相似文献