Comparison of the effects of certain thiol reagents on alanine transport in plasma membrane vesicles from rat liver and their use in identifying the alanine carrier.
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ABSTRACT:
SUBMITTER: Hayes MR
PROVIDER: S-EPMC1152271 | biostudies-other | 1983 Aug
REPOSITORIES: biostudies-other
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Project description:1. In the present study we have examined the sensitivity of A and ASC amino-acid-carrier activities in rat liver plasma-membrane vesicles to the thiol-group modifying reagents N-ethylmaleimide (NEM) and iodoacetamide (IA). To this end, the different Na(+)-dependent entities involved in alanine transport were assessed. 2. NEM inactivated Na(+)-dependent alanine transport as a result of the inhibition of both system A and ASC transport activities. The functional sensitivity of system A to NEM was greater than that of system ASC. 3. The presence of L-alanine (10 mM) during the exposure of vesicles to NEM afforded partial protection to system A, but not to the ASC, carrier. This effect was specific, since the presence of L-phenylalanine (10 mM) did not cause any protection. 4. Na+ did not protect A or ASC carriers against NEM inactivation; however, the presence of Na+ (100 mM-NaCl) and L-alanine (10 mM) during the exposure of the vesicles to NEM protected against inactivation of system A and ASC transport activities. The extent of protection was greater in the case of the system ASC transport activity than in the case of the A carrier. 5. IA also diminished Na(+)-dependent alanine transport by inhibition of A and ASC transport activities. Sodium and L-alanine afforded protection to both A and ASC transport activities from the inhibitory action of IA. The extent of protection induced by substrates was similar for both carriers. 6. It is concluded that there is one, or several, free thiol groups in A and ASC carriers, the integrity of which is essential for transport activity. Sensitivity to thiol-group-specific reagents and the pattern of protection with substrates against inactivation is different in A and ASC carriers. That suggests the existence of topological dissimilarities regarding the thiol-group containing site(s) in A and ASC amino acid carriers.
| S-EPMC1149553 | biostudies-other
Project description:Sulfhydryl-containing compounds, including thiols and hydrogen sulfide (H2S), play important but differential roles in biological structure and function. One major challenge in separating the biological roles of thiols and H2S is developing tools to effectively separate the reactivity of these sulfhydryl-containing compounds. To address this challenge, we report the differential responses of common electrophilic fluorescent thiol labeling reagents, including nitrobenzofurazan-based scaffolds, maleimides, alkylating agents, and electrophilic aldehydes, toward cysteine and H2S. Although H2S reacted with all of the investigated scaffolds, the photophysical response to each scaffold was significantly different. Maleimide-based, alkylating, and aldehydic thiol labeling reagents provided a diminished fluorescence response when treated with H2S. By contrast, nitrobenzofurazan-based labeling reagents were deactivated by H2S addition. Furthermore, the addition of H2S to thiol-activated nitrobenzofurazan-based reagents reduced the fluorescence signal, thus establishing the incompatibility of nitrobenzofurazan-based thiol labeling reagents in the presence of H2S. Taken together, these studies highlight the differential reactivity of thiols and H2S toward common thiol-labeling reagents and suggest that sufficient care must be taken when labeling or measuring thiols in cellular environments that produce H2S due to the potential for both false-positive and eroded responses.
| S-EPMC4063329 | biostudies-literature
Project description:The thiol reagent dithiothreitol inhibits the activity of a core GDP-fucose-N-acetylglucosaminide alpha-6-fucosyltransferase in plasma and blood-cell homogenates, while promoting the activity of alpha-2- and alpha-3-fucosyltransferases. The latter enzymes catalyse transfer of fucose on to terminal galactose and subterminal N-acetylglucosamine residues respectively. A thiol-blocking reagent N-ethylmaleimide does not affect the activity of the alpha-6-fucosyltransferase, but inhibits the other two enzymes. These results indicate the presence of a critical disulphide linkage in the alpha-6-fucosyltransferase, and provide a means of delineation of different fucosyltransferases.
| S-EPMC1161218 | biostudies-other
Project description:1. The ability of phlorrhizin to inhibit the galactosylation of glucose was re-examined with Golgi membrane vesicles purified from rat mammary gland, and extended to the galactosylation of several glucose analogues and N-acylglucosamines. 2. The inhibition is ascribed, contrary to previous conclusions, to a general annealing of leaky membranes comprising a minority of the vesicles. 3. Three thiol reagents were able to inhibit the galactosylation of N-acylglucosamines with less, or no, inhibition of galactosylation of glucose. This demonstrates the existence of a Golgi membrane carrier that distinguishes between glucose and N-acylglucosamines.
| S-EPMC1161894 | biostudies-other
Project description:A carrier-free CRISPR/Cas9 ribonucleoprotein delivery strategy for genome editing mediated by a cold atmospheric plasma (CAP) is described. The CAP is promising in many biomedical applications due to efficient production of bioactive ionized species. The MCF-7 cancer cells after CAP exposure exhibit increased extracellular reactive oxygen and nitrogen species (RONS) and altered membrane potential and permeability. Hence, transmembrane transport of Ca2+ into the cells increases and accelerates ATP hydrolysis, resulting in enhanced ATP-dependent endocytosis. Afterwards, the increased Ca2+ and ATP contents promote the release of cargo into cytoplasm due to the enhanced endosomal escape. The increased membrane permeability also facilitates passive diffusion of foreign species across the membrane into the cytosol. After CAP exposure, the MCF-7 cells incubated with Cas9 ribonucleoprotein (Cas9-sgRNA complex, Cas9sg) with a size of about 15 nm show 88.9% uptake efficiency and 65.9% nuclear import efficiency via passive diffusion and ATP-dependent endocytosis pathways. The efficient transportation of active Cas9sg after the CAP treatment leads to 21.7% and 30.2% indel efficiencies in HEK293T and MCF-7 cells, respectively. This CAP-mediated transportation process provides a simple and robust alternative for the delivery of active CRISPR/Cas9 ribonucleoprotein. Additionally, the technique can be extended to other macro-biomolecules and nanomaterials to cater to different biomedical applications.
| S-EPMC8533602 | biostudies-literature
Project description:Transport of [14C]tetraethylammonium (TEA), an organic cation, was studied in brush-border (BBMV) and basolateral (BLMV) membrane vesicles isolated from rabbit kidney cortex. In BBMV, the presence of an outwardly directed H+ gradient induced a marked stimulation of TEA uptake against its concentration gradient (overshoot phenomenon), whereas a valinomycin-induced inside-negative potential had no effect on TEA uptake. In BLMV, TEA uptake was significantly stimulated by the presence of an outwardly directed H+ gradient and by an inside-negative potential, but the effect of H+ gradient was absent when the vesicles were chemically 'voltage clamped'. In BBMV, internal H+ stimulated TEA uptake in a non-competitive manner by binding at a site with apparent pKa of 6.87. External H+ inhibited TEA uptake through a direct interaction with the putative H+/organic-cation exchanger at a site with apparent pKa of 6.78. Changing external pH while maintaining the pH gradient constant produced a result similar to that obtained by changing external pH alone. Increasing external H+ showed a mixed-type inhibition of TEA uptake. These results suggest that in the rabbit TEA transport across the basolateral membranes is driven by an inside-negative potential and that transport across the brush-border membrane is driven by a H+ gradient via an electroneutral H+/TEA antiport system.
| S-EPMC1138521 | biostudies-other
Project description:The mechanism of exit of folate from the enterocyte, i.e. transport across the basolateral membrane, is not known. In this study we examined, using basolateral membrane vesicles, the transport of folic acid across the basolateral membrane of rat intestine. Uptake of folic acid by these vesicles represents transport of the substrate into the intravesicular compartment and not binding to the membrane surface. The rate of folic acid transport was linear for the first 1 min of incubation but decreased thereafter, reaching equilibrium after 5 min of incubation. The transport of folic acid was: (1) saturable as a function of concentration with an apparent Km of 0.6 +/- 0.17 microM and Vmax. of 1.01 +/- 0.11 pmol/30 s per mg of protein; (2) inhibited in a competitive manner by the structural analogues 5-methyltetrahydrofolate and methotrexate (Ki = 2 and 1.4 microM, respectively); (4) electroneutral; (5) Na+-independent; (6) sensitive to the effect of the anion exchange inhibitor 4,4'-di-isothiocyanatostilbene-2,2'-disulphonic acid (DIDS). These data indicate the existence of a carrier-mediated transport system for folic acid in rat intestinal basolateral membrane and demonstrate that the transport process is electroneutral, Na+-independent and sensitive to the effect of anion exchange inhibition.
| S-EPMC1148380 | biostudies-other
Project description:L-Glutamine, a major energy substrate for intestinal epithelial cells, can be extracted from intraluminal contents across the brush-border membrane and from arterial blood via the basolateral membrane. The purpose of the present study was to characterize glutamine transport by the basolateral membrane of rabbit epithelial cells. Transport of glutamine by isolated basolateral-membrane vesicles was mediated by both Na(+)-dependent and Na(+)-independent carriers. Tests were performed to distinguish glutamine uptake by likely transport agencies, including Systems A, ASC, N, IMINO, NBB, L and asc. The Na(+)-dependent glutamine uptake was strongly inhibited by an excess of 2-(methylamino)isobutyric acid (MeAIB), and glutamine was equally effective in inhibiting MeAIB transport. The reciprocal inhibition analysis, as well as a sensitivity to increased H+ concentration, indicates that Na(+)-dependent glutamine transport across the basolateral membrane is mediated by System A. The saturable Na(+)-independent glutamine transport was markedly inhibited by 2-aminobicyclo-[2,2,1]-heptane-2-carboxylic acid ('BCH') and insensitive to changes in assay pH, suggesting uptake via System L rather than System asc. The presence of a Na(+)-dependent carrier to mediate active transport of glutamine across the basolateral membrane is probably essential to ensure a continuous supply of this vital substrate to the enterocyte in the post-absorptive state.
| S-EPMC1151298 | biostudies-other
Project description:1. Transport of glycine has been demonstrated in membrane vesicles isolated from rat brain, using artificially imposed ion gradients as the sole energy source. 2. The uptake of glycine is strictly dependent on the presence of Na+ and Cl- in the medium, and the process can be driven either by an Na+ gradient (out greater than in) or by a C1- gradient (out greater than in) when the other essential ion is present. 3. The uptake of glycine is stimulated by a membrane potential (interior negative), as demonstrated by the effects of the ionophores valinomycin and carbonyl cyanide m-chlorophenylhydrazone and anions of different permeabilities. 4. The kinetic analysis shows that glycine is accumulated by two systems with different affinities. 5. The presence of ouabain, an inhibitor (Na+ + K+)-activated ATPase, does not affect glycine transport. 6. The existence of a high-affinity, Na+-dependent glycine-uptake system in membrane vesicles derived from rat brain suggests that this amino acid may have a transmitter role in some areas of the rat brain.
| S-EPMC1163299 | biostudies-other
Project description:Background: Acute coronary syndromes (ACS) are associated with aberrant gene expression and epigenetic mechanisms. In particular, de novo DNA methylation is typically linked to gene silencing, but its role in heart disease remains not fully understood. Extracellular vesicles (EVs) are active components in cellular communication for their ability to carry a plethora of signalling biomolecules, thus representing a promising new diagnostic/therapeutic approach in cardiovascular diseases (CVDs). Indeed, there is the need of novel biomarkers for ACS prediction and timely detection. Purpose: We hypothesized that specific epigenetic signals can be carried by EVs. In this regard, we isolated and characterized circulating EVs from ACS patients and evaluated their potential role to influence DNA methylation in target cells. Methods: Circulating EVs were recovered, by ultracentrifugation, from plasma samples of 19 ACS patients and 50 healthy subjects (HS). Nanoparticle tracking analysis (NTA) and western blot (WB) were used to confirm the EVs integrity and purity. Peripheral blood mononuclear cells (PBMCs) of volunteer donors were treated with both ACS and HS derived EVs and genomic DNA was extracted to perform epigenome wide analysis through Reduced Representation Bisulfite Sequencing. ShinyGO, PANTHER, and STRING tools were interrogated to perform GO and PPI network analyses. Flow Cytometry, qRT-PCR, and WB analysis were also performed to evaluate and validate both intra-vesicular and intra-cellular signals. Results: Plasma ACS-derived EVs showed a significant up-regulation of DNA methyltransferases (DNMTs) gene expression levels as compared to HS (P<0.001). Specifically, de novo methylation transcripts, as DNMT3A and DNMT3B were significantly increased in plasma ACS-EVs. DNA methylation analysis of PBMCs from volunteer donors treated with HS- and ACS-derived EVs showed that RNF166 and CCND3 genes resulted the most hyper- and hypo-methylated, respectively, after by ACS-EV treatment. In addition, PPI network analysis specifically evidenced the subnetwork with SRC, as a hub gene, connecting it to NOTCH1, FOXO3, CDC42, IKBKG, RXRA, DGKG, known as important genes already involved in the onset of CVDs. Surprising, other novel genes, BAIAP2, SYP, CHL1, and SHB, which were hypomethylated, were found significantly overexpressed in PBMCs (P<0.005), underlying the fundamental modulating properties of EV cargo in atherosclerosis. Conclusions: These findings support the significant role of ACS plasma-derived EVs, inducing de novo DNA methylation signals, and modulating specific signaling pathways in target cells.
2023-04-03 | E-MTAB-11641 | biostudies-arrayexpress