Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P50583 (asymmetrical)
 12,197 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The characteristics of L-lysine transport were investigated at brush-border (maternal) and basal (fetal) sides of the syncytiotrophoblast in the term guinea-pig placenta artificially perfused either through the umbilical vessels in situ or through both circulations simultaneously. Cellular uptake, efflux and transplacental transfer were determined using a single-circulation paired-tracer dilution technique. Unidirectional L-[3H]lysine uptake (%) (perfusate lysine 50 microM) was high on maternal (M = 87 +/- 1) and fetal (F = 73 +/- 2) sides. L-[3H]Lysine efflux back into the ipsilateral circulation was asymmetrical (F/M ratio = 2.3) and transplacental flux occurred in favour of the fetal circulation. Unidirectional lysine influx kinetics (0.05-8.00 mM) gave Km values of 1.75 +/- 0.70 mM and 0.90 +/- 0.25 mM at maternal and fetal sides, respectively; corresponding Vmax values were 1.95 +/- 0.38 and 0.87 +/- 0.10 mumol.min-1.g-1. At both sides, lysine influx (50 microM) could be inhibited (about 60-80%) by 4 mM L-lysine and L-ornithine and less effectively (about 10-40%) by L-citrulline, L-arginine, D-lysine and L-histidine. At the basal side: (i) lysine influx kinetics were greatly modified in the presence of 10 mM L-alanine (Km = 6.25 +/- 3.27 mM; Vmax = 2.62 +/- 0.94 mumol.min-1.g-1), but unchanged by equimolar L-phenylalanine or L-tryptophan; (ii) in the converse experiments, lysine (10 mM) did not affect the kinetic characteristics for either L-alanine or L-phenylalanine; (iii) L-lysine and L-alanine influx kinetics were not dependent on the sodium gradient; (iv) the inhibition of L-[3H]lysine uptake by 4 mM L-homoserine was partially (60%) Na+-dependent. At the maternal side the kinetic characteristics for alanine influx were highly Na+-dependent, while lysine influx was partially Na+-dependent only at low concentrations (0.05-0.5 mM). Bilateral perfusion with 2,4-dinitrophenol (1 mM) reduced L-[3H]lysine uptake into the trophoblast and abolished transplacental transfer. It is suggested that lysine transport in the guinea-pig placenta is mediated by a specific transport system (y+) for cationic amino-acids. The asymmetry in the degree of sodium-dependency at both trophoblast membranes may in part explain the maternal-to-foetal polarity of placental amino-acid transfer in vivo.
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PMID:Lysine and alanine transport in the perfused guinea-pig placenta. 249 34

The exit of alanine across the serosal border of the epithelial cells of turtle intestine was measured by direct and indirect techniques. A decrease or an increase in cell Na did not affect the amino acid flux from cell to serosal solution. Cells loaded with Na and alanine did not exhibit any extrusion of alanine when their serosal membranes were exposed to an Na-free medium containing alanine. However, substantial amino acid extrusion was observed across the mucosal cell border under similar conditions. Although alanine flux across the serosal membrane appeared to be Na-independent, it showed a tendency toward saturation as cellular alanine concentration was elevated. The results are consistent with the postulate that the serosal and mucosal membranes of intestinal cells are asymmetrical with respect to amino acid transport mechanisms. The serosal membrane appears to have an Na-independent carrier-mediated mechanism responsible for alanine transport while transport across the mucosal border involves an Na-dependent process.
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PMID:Alanine efflux across the serosal border of turtle intestine. 464 78

The folding of short alanine-based peptides with different numbers of lysine residues is simulated at constant temperature (274 K) using the rigid-element Monte Carlo method. The solvent-referenced potential has prevented the multiple-minima problem in helix folding. From various initial structures, the peptides with three lysine residues fold into helix-dominated conformations with the calculated average helicity in the range of 60-80%. The peptide with six lysine residues shows only 8-14% helicity. These results agree well with experimental observations. The intramolecular electrostatic interaction of the charged lysine side chains and their electrostatic hydration destabilize the helical conformations of the peptide with six lysine residues, whereas these effects on the peptides with three lysine residues are small. The simulations provide insight into the helix-folding mechanism, including the beta-bend intermediate in helix initiation, the (i, i + 3) hydrogen bonds, the asymmetrical helix propagation, and the asymmetrical helicities in the N- and C-terminal regions. These findings are consistent with previous studies.
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PMID:Folding simulations of alanine-based peptides with lysine residues. 775 50

A competitive reaction of activated Boc-Ala-OH and Boc-Phe-OH with H-Leu-resin has been developed for assessing the relative efficiencies of different carbodiimides. This allowed a comparison of the efficiency of the carbodiimides N,N'-dicyclohexylcarbodiimide,N,N'-diisopropylcarbodiimide, N-tert-butyl-N'-methylcarbodiimide and N-tert-butyl-N'-ethylcarbodiimide. Comparable results were obtained when these reagents were used for the preformation of symmetrical anhydrides or of 1-hydroxybenzotriazole esters in situ. Differential incorporation was observed when asymmetrical carbodiimides were used for peptide bond formation by the direct carbodiimide procedure.
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PMID:Evaluation of carbodiimides using a competition method. 923 Apr 79

The amidated tetrapeptide Ala-Pro-Gly-Trp-NH2 (APGWamide) plays a key role in the control of male copulation behavior in the basommatophoran pulmonate freshwater snail Lymnaea stagnalis. The morphological basis for a conserved role of APGWamide in the control of male reproduction in gastropod molluscs is presented. The prosobranch Littorina littorea, the opisthobranch Aplysia californica, the basommatophoran pulmonate Bulinus truncatus, and the stylommatophoran pulmonates Arion ater and Limax maximus have been examined for the presence of APGWamide producing neurons using immunocytochemistry and in situ hybridization. In all species investigated a cluster of APGWamide expressing neurons is present in the anteromedial region of the cerebral ganglia. The asymmetrical distribution which exists in Lymnaea and which coincides with the innervation of the asymmetrically located penial complex is also found in the opisthobranch Aplysia, as well as in the stylommatophoran pulmonate slugs Arion and Limax, in which APGWamide immunoreactive neurons are only found in the mesocerebrum of the right cerebral ganglion. APGWamide immunoreactive varicose fibers innervate muscles of the male accessory sex organs in Bulinus and Aplysia, confirming the hypothesis that APGWamide may be a biochemically and functionally conserved factor in the regulation of gastropod mollusc reproduction.
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PMID:Localization of the neuropeptide APGWamide in gastropod molluscs by in situ hybridization and immunocytochemistry. 947 61

The metabolism of [2,3-13C]succinic acid dimethyl ester ([2,3-13C]-SAD) 10 mmol/L was examined in hepatocytes from overnight-fasted normal rats, 3-day starved rats, and overnight-fasted hereditarily diabetic Goto-Kakizaki (GK) rats. The amount of 13C-labeled succinate, fumarate, malate, lactate, alanine, and aspartate released by the hepatocytes was much higher in fasted normal rats than in starved or diabetic animals. Although the integrated areas of the 13C2 and 13C3 signals assigned to double-labeled malate, lactate, or alanine were not significantly different, the amount of single-labeled malate, lactate, alanine, and aspartate was higher in C3- versus C2-labeled isotopomers. The release of 13C-labeled glucose by the hepatocytes was lower in fasted versus starved or diabetic rats. Virtually all hexose molecules double-labeled in the C1-C2-C3 and/or C6-C5-C4 moieties corresponded to the [1,2-13C] and/or [5,6-13C] isotopomers. However, in the case of the single-labeled species, 13C-labeling of C1 (or C6) exceeded that of C2 (or C5). Both the single- and double-labeled molecules enriched with 13C in the C1-C2-C3 moiety were less abundant than those labeled in the C6-C5-C4 moiety, with such asymmetry being most marked in overnight-fasted normal rats, less pronounced in diabetic animals, and virtually absent in starved rats. These findings document that SAD is efficiently metabolized in hepatocytes, with its use as a gluconeogenic precursor being influenced by the nutritional and hormonal status of the animals. The present experiments also reinforce the view that asymmetrical labeling of glucose by 13C-labeled precursors is modulated by the relative contribution of exogenous and endogenous nutrients to the production of triose phosphates incorporated into the hexose.
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PMID:Effects of starvation and diabetes on the metabolism of [2,3-13C]succinic acid dimethyl ester in rat hepatocytes. 992 Jan 52

This investigation was aimed to prove the asymmetrical interactions of polarized electrons from 90Sr-90Y-beta-decay with D- and L-alanines. By use of ESR measurements, it was determined that the asymmetrical yields induced in 90Sr-90Y-beta-irradiated alanines are 10% more in D-alanine than in L-alanine.
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PMID:Investigation on the asymmetrical induced yields in 90Sr- 90Y-beta-irradiated D- and L-alanines. 1153 68

The contributions to substrate binding and catalysis of 13 amino acid residues of the Caenorhabditis elegans diadenosine tetraphosphate pyrophosphohydrolase (Ap(4)A hydrolase) predicted from the crystal structure of an enzyme-inhibitor complex have been investigated by site-directed mutagenesis. Sixteen glutathione S-transferase-Ap(4)A hydrolase fusion proteins were expressed and their k(cat) and K(m) values determined after removal of the glutathione S-transferase domain. As expected for a Nudix hydrolase, the wild type k(cat) of 23 s(-1) was reduced by 10(5)-, 10(3)-, and 30-fold, respectively, by replacement of the conserved P(4)-phosphate-binding catalytic residues Glu(56), Glu(52), and Glu(103) by Gln. K(m) values were not affected, indicating a lack of importance for substrate binding. In contrast, mutating His(31) to Val or Ala and Lys(83) to Met produced 10- and 16-fold increases in K(m) compared with the wild type value of 8.8 microm. These residues stabilize the P(1)-phosphate. H31V and H31A had a normal k(cat) but K83M showed a 37-fold reduction in k(cat). Lys(36) also stabilizes the P(1)-phosphate and a K36M mutant had a 10-fold reduced k(cat) but a relatively normal K(m). Thus both Lys(36) and Lys(83) may play a role in catalysis. The previously suggested roles of Tyr(27), His(38), Lys(79), and Lys(81) in stabilizing the P(2) and P(3)-phosphates were not confirmed by mutagenesis, indicating the absence of phosphate-specific binding contacts in this region. Also, mutating both Tyr(76) and Tyr(121), which clamp one substrate adenosine moiety between them in the crystal structure, to Ala only increased K(m) 4-fold. It is concluded that interactions with the P(1)- and P(4)-phosphates are minimum and sufficient requirements for substrate binding by this class of enzyme, indicating that it may have a much wider substrate range then previously believed.
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PMID:Analysis of the catalytic and binding residues of the diadenosine tetraphosphate pyrophosphohydrolase from Caenorhabditis elegans by site-directed mutagenesis. 1247 70

Salivarian trypanosomes use antigenic variation of their variant-specific surface glycoprotein (VSG) coat as a defense against the host immune system. Although about 1000 VSG and pseudo-VSG genes are scattered throughout the trypanosome genome, each trypanosome expresses only one VSG, while the rest of the genes are transcriptionally silent. A 64-kDa glycosylated cross-reacting antigen between Trypanosoma evansi and Trypanosoma vivax (p64), which was purified from the TEVA1 T. evansi Venezuelan isolate, was proven here to represent the soluble form of a VSG. Initially, a biochemical characterization of p64 was carried out. Gel filtration chromatography, sedimentation, and chemical cross-linking provided evidences of the dimeric nature of p64. The hydrodynamic parameters indicated that p64 is asymmetrical with a frictional ratio f/fo = 1.57. Isoelectric focusing and two-dimensional polyacrylamide gel electrophoresis revealed that p64 contained two isoforms with isoelectric points of 6.8-6.9 and 7.1-7.2. When p64 and three p64 Staphylococcus aureus V8 proteolytic fragments were sequenced, the same N-termini sequence was obtained: Ala-Pro-Ile-Thr-Asp-Ala-Asp-Leu-Gly-Pro-Ala-Gln-Ile-Ala-Asp, which displayed a significant homology with a putative Trypanosoma brucei VSG gene located on chromosome 4. Additionally, immunofluorescence microscopy on T. evansi and T. vivax established that p64 and its T. vivax homologue were confined to the surface of both parasites. An immunological characterization of this antigen was also carried out using several Venezuelan T. evansi isolates expressing different VSGs, which were obtained from naturally infected animals. Although sera from animals infected with the various T. evansi isolates recognized p64, only one isolate, besides TEVA1, contained polypeptides that were recognized by anti-p64 antibodies. All these results together with prior evidences [Uzcanga, G. et al. (2002) Parasitology 124, 287-299] confirmed that p64 is the soluble form of a T. evansi VSG, containing common epitopes recognized by sera from animals infected with T. evansi or T. vivax. Despite the huge repertoire of VSG genes existing on bloodstream trypanosomes, our data also demonstrated the potential use of a VSG variant from the TEVA1 T. evansi isolate as a diagnostic reagent.
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PMID:Variant surface glycoprotein from Trypanosoma evansi is partially responsible for the cross-reaction between Trypanosoma evansi and Trypanosoma vivax. 1473 Sep 63

The glutamine/amino acid transporter was solubilized from rat renal apical plasma membrane (brush-border membrane) with C12E8 and reconstituted into liposomes by removing the detergent from mixed micelles by hydrophobic chromatography on Amberlite XAD-4. The reconstitution was optimised with respect to the protein concentration, the detergent/phospholipid ratio and the number of passages through a single Amberlite column. The reconstituted glutamine/amino acid transporter catalysed a first-order antiport reaction stimulated by external, not internal, Na+. Optimal activity was found at pH 7.0. The sulfhydryl reagents HgCl2, mersalyl and p-hydroxymercuribenzoate and the amino acids alanine, serine, threonine, cysteine, asparagine, methionine and valine strongly inhibited the transport, whereas the amino acid analogue methylaminoisobutyrate had no effect. Glutamine, alanine, serine, asparagine, threonine were efficiently translocated from outside to inside and from inside to outside the proteoliposomes as well. Cysteine and valine were translocated preferentially from outside to inside. The Km for glutamine on the external and internal side of the transporter was 0.47 and 11 mM, respectively; the values were not influenced by the type of the counter substrate. The transporter is functionally asymmetrical and it is unidirectionally inserted into the proteoliposomal membrane with an orientation corresponding to that of the native membrane. By a bisubstrate kinetic analysis of the glutamine antiport, a random simultaneous mechanism was found. The glutamine antiport was strongly stimulated by internal nucleoside triphosphates and, to a lower extent, by pyrophoshate. The reconstituted glutamine/amino acid transporter functionally corresponds to the ASCT2 protein.
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PMID:Reconstitution into liposomes of the glutamine/amino acid transporter from renal cell plasma membrane: functional characterization, kinetics and activation by nucleotides. 1558 47


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