Search results for "succinate"
showing 10 items of 105 documents
Toward Mechanistic Design of Surrogate Buffers for Dissolution Testing of pH-Dependent Drug Delivery Systems
2020
The in vivo dissolution of enteric-coated (EC) products is often overestimated by compendial in vitro dissolution experiments. It is of great interest to mimic the in vivo conditions as closely as possible in vitro in order to predict the in vivo behavior of EC dosage forms. The reason behind this is the overly high buffering capacity of the common compendial buffers compared to the intestinal bicarbonate buffer. However, a bicarbonate-based buffer is technically difficult to handle due to the need for continuous sparging of the media with CO2 to maintain the desired buffer pH. Therefore, bicarbonate buffers are not commonly used in routine practice and a non-volatile alternative is of inte…
Effects of the herbicides Benzoylpropethyl and flampropisopropyl on rat liver mitochondria : an alteration in membrane fluidity ?
1984
Abstract The action of the herbicides benzoylpropethyl and flampropisopropyl, and the corresponding unesterified acids was studied in rat liver mitochondria. The herbicides were found to (a) inhibit the mitochondrial electron transfer in complex III or at the level of ubiquinone (I50 of 4 nmol mg protein−1 for flampropisopropyl and 18 for benzoylpropethyl with succinate as a substrate); (b) have an additional (however less sensitive) site of inhibition near succinate dehydrogenase; and (c) interfere with energy transfer. Sensitivity was increased 2- (benzoylpropethyl) and 3.5-fold (flampropisopropyl) as the rats age increased from 12–13 weeks to 23–26 weeks. The free acids were far less eff…
Fumarate regulation of gene expression in Escherichia coli by the DcuSR (dcuSR genes) two-component regulatory system.
1998
ABSTRACT In Escherichia coli the genes encoding the anaerobic fumarate respiratory system are transcriptionally regulated by C 4 -dicarboxylates. The regulation is effected by a two-component regulatory system, DcuSR, consisting of a sensory histidine kinase (DcuS) and a response regulator (DcuR). DcuS and DcuR are encoded by the dcuSR genes (previously yjdHG ) at 93.7 min on the calculated E. coli map. Inactivation of the dcuR and dcuS genes caused the loss of C 4 -dicarboxylate-stimulated synthesis of fumarate reductase ( frdABCD genes) and of the anaerobic fumarate-succinate antiporter DcuB ( dcuB gene). DcuS is predicted to contain a large periplasmic domain as the supposed site for C 4…
Fumarate respiration of Wolinella succinogenes: enzymology, energetics and coupling mechanism.
2002
Wolinella succinogenes performs oxidative phosphorylation with fumarate instead of O2 as terminal electron acceptor and H2 or formate as electron donors. Fumarate reduction by these donors ('fumarate respiration') is catalyzed by an electron transport chain in the bacterial membrane, and is coupled to the generation of an electrochemical proton potential (Deltap) across the bacterial membrane. The experimental evidence concerning the electron transport and its coupling to Deltap generation is reviewed in this article. The electron transport chain consists of fumarate reductase, menaquinone (MK) and either hydrogenase or formate dehydrogenase. Measurements indicate that the Deltap is generat…
Methylprednisolone neutralizes the beneficial effects of erythropoietin in experimental spinal cord injury
2005
Inflammation plays a major pathological role in spinal cord injury (SCI). Although antiinflammatory treatment using the glucocorticoid methyprednisolone sodium succinate (MPSS) improved outcomes in several multicenter clinical trials, additional clinical experience suggests that MPSS is only modestly beneficial in SCI and poses a risk for serious complications. Recent work has shown that erythropoietin (EPO) moderates CNS tissue injury, in part by reducing inflammation, limiting neuronal apoptosis, and restoring vascular autoregulation. We determined whether EPO and MPSS act synergistically in SCI. Using a rat model of contusive SCI, we compared the effects of EPO [500-5,000 units/kg of bod…
Reduced Apo-Fumarate Nitrate Reductase Regulator (ApoFNR) as the Major Form of FNR in Aerobically Growing Escherichia coli▿
2008
ABSTRACT Under anoxic conditions, the Escherichia coli oxygen sensor FNR (fumarate nitrate reductase regulator) is in the active state and contains a [4Fe-4S] cluster. Oxygen converts [4Fe-4S]FNR to inactive [2Fe-2S]FNR. After prolonged exposure to air in vitro, apoFNR lacking a Fe-S cluster is formed. ApoFNR can be differentiated from Fe-S-containing forms by the accessibility of the five Cys thiol residues, four of which serve as ligands for the Fe-S cluster. The presence of apoFNR in aerobically and anaerobically grown E. coli was analyzed in situ using thiol reagents. In anaerobically and aerobically grown cells, the membrane-permeable monobromobimane labeled one to two and four Cys res…
O2 as the regulatory signal for FNR-dependent gene regulation in Escherichia coli
1996
With an oxystat, changes in the pattern of expression of FNR-dependent genes from Escherichia coli were studied as a function of the O2 tension (pO2) in the medium. Expression of all four tested genes was decreased by increasing O2. However, the pO2 values that gave rise to half-maximal repression (pO(0.5)) were dependent on the particular promoter and varied between 1 and 5 millibars (1 bar = 10(5) Pa). The pO(0.5) value for the ArcA-regulated succinate dehydrogenase genes was in the same range (pO(0.5) = 4.6 millibars). At these pO2 values, the cytoplasm can be calculated to be well supplied with O2 by diffusion. Therefore, intracellular O2 could provide the signal to FNR, suggesting that…
Inability of rat alveolar macrophages to recycle l-citrulline to l-arginine despite induction of argininosuccinate synthetase mRNA and protein, and i…
1998
In the present study it was tested whether rat alveolar macrophages (AMphi) convert L-citrulline to L-arginine to maintain nitric oxide (NO) synthesis under conditions of limited availability of L-arginine. Rat AMphi (0.5 x 10(6) cells/well, cultured for 20 h in the absence or presence of 1 microg/ml lipopolysaccharides, LPS), were incubated for 6 h in amino acid-free Krebs solution and nitrite accumulation was determined as a measure of NO synthesis. After culture in the absence of LPS, nitrite in the incubation media was at the detection limit, independent of the addition of L-arginine or L-citrulline. AMphi, cultured in the presence of LPS, produced about 4 nmol per 10(6) cells and 6 h n…
DIFFERENTIAL SCANNING CALORIMETRY STUDY ON DRUG RELEASE FROM AN INULIN-BASED HYDROGEL AND ITS INTERACTION WITH A BIOMEMBRANE MODEL:pH AND LOADING EFF…
2008
Inulin has been derivatized with methacrylic anhydride (MA) and succinic anhydride (SA) to obtain a methacrylated/succinilated derivative (INU-MA-SA) able to produce a pH sensitive hydrogel after UV irradiation. The hydrogel was characterized and loaded with diflunisal (10.4, 17 and 24%, w/w) chosen as a model drug. The drug release from INU-MA-SA-based hydrogel to a biomembrane model made by unilamellar vesicles of dimyristoylphosphatidyl-choline (DMPC) was investigated at pH 4.0 and 7.4 by differential scanning calorimetry (DSC) that appears to be a suitable technique to follow the transfer kinetics of a drug from a controlled release system to a biomembrane model. The drug release from t…
Head and neck paragangliomas: Report of 175 patients (1989-2010)
2011
Attention of the otorhinolaryngologist needs to be drawn to the versatile aspects of head and neck paragangliomas (PGLs).This study is a retrospective, nonrandomized clinical study of all 175 individuals with PGLs treated in our department between 1989 and 2010. A genetic analysis was performed on 86 patients.The 175 patients presented 224 head and neck PGLs as well as 2 thyroid papillary carcinomas. Genetic analysis resulted in 1 patient positive for a von Hippel-Lindau (VHL) gene mutation and 34 for succinate dehydrogenase (SDH) gene mutations (22 SDHD, 7 SDHC, and 5 SDHB), 12 of the latter carrying a novel mutation. Thirty-three patients (18.9%) had multiple PGLs and 11 patients (6.3%) h…