Research in bioethics: a bridge between science and philosophy

Radioiodinated (R)-quinuclidinyl-4-iodobenzilate (4IQNB) is a high affinity muscarinic antagonist which has been utilized for in vitro and in vivo assays, and for SPECT imaging in humans. 4IQNB exists in four different diastereomeric forms, since there are two asymmetric centers at the quinuclidinyl and benzilic acid centers. Based upon our in vivo studies, we have determined that the absolute stereochemistry previously assigned to the benzilic center was incorrect for the diastereomer that had been previously referred to as '(R)-quinuclidinyl-(R)-4-iodobenzilate' [(R,R)-4IQNB]. The correct designation for this diastereomer is '(R)-quinuclidinyl-(S)-4-iodobenzilate' [(R,S)-4IQNB].     

Gibbilimbols A-D, cytotoxic and antibacterial alkenylphenols from Piper gibbilimbum

Fractionation of the petroleum ether extract from the leaves of Piper gibbilimbum collected in Papua New Guinea afforded four new alkenylphenols, gibbilimbols A-D (1-4). The structures of the isolates were elucidated by spectroscopic methods, mainly 1D- and 2D-NMR spectroscopy. Gibbilimbols A-D were found to be toxic to brine shrimp with an LC50 of approximately 5 microg/mL. Gibbilimbols A-D were further found to be cytotoxic toward KB nasopharyngal carcinoma cells (ED50 7.8-2.1 microg/mL). All isolates also showed antibacterial activity toward Staphylococcus epidermidis and Bacillus cereus.     

Subunit composition, crystallization and preliminary crystallographic studies of the Desulfovibrio gigas aldehyde oxidoreductase containing molybdenum and [2Fe-2S] centers

The Desulfovibrio gigas aldehyde oxidoreductase contains molybdenum bound to a pterin cofactor and [2Fe-2S] centers. The enzyme was characterized by SDS/PAGE, gel-filtration and analytical ultracentrifugation experiments. It was crystallized at 4 degrees C, pH 7.2, using isopropanol and MgCl2 as precipitants. The crystals diffract beyond 0.3-nm (3.0-A) resolution and belong to space group P6(1)22 or its enantiomorph, with cell dimensions a = b = 14.45 nm and c = 16.32 nm. There is one subunit/asymmetric unit which gives a packing density of 2.5 x 10(-3) nm3/Da (2.5 A3/Da), consistent with the experimental crystal density, rho = 1.14 g/cm3. One dimer (approximately 2 x 100 kDa) is located on a crystallographic twofold axis.     

Synthesis and morphological reversion activity on srctsNRK cells of pyrimidinylpropanamide antibiotics, sparsomycin, sparoxomycin A1, A2, and their analogues

Three pyrimidinylpropanamide antibiotics sparsomycin (1), sparoxomycins A1, A2 (2, 3), and also six analogues (4-9) have been synthesized by employing asymmetric sulfide oxidation conditions as a key step. Sparsomycin (1) and its alkyl analogues (5-7) showed higher morphological reversion activities on srctsNRK cells than 2 and 3.     

Synthesis and biological evaluation of the enantiomers of the potent and selective A1-adenosine antagonist 1,3-dipropyl-8-[2-(5,6-epoxynorbonyl)]-xanthine

The individual enantiomers 8 and 12 of the potent and highly selective racemic A1-adenosine antagonist 1,3-dipropyl-8-[2-(5,6-epoxynorbornyl)]xanthine (ENX, 4) were synthesized utilizing asymmetric Diels-Alder cycloadditions for the construction of the norbornane moieties. The absolute configuration of 12 was determined by X-ray crystallography of the 4-bromobenzoate 14, which was derived from the bridged secondary alcohol 13. The latter was obtained from 12 by an acid-catalyzed intramolecular rearrangement. The binding affinities of the enantiomers 8 and 12 and the racemate 4 at guinea pig, rat, and cloned human A1- and A2a-adenosine receptor subtypes were determined. The S-enantiomer 12 (CVT-124) appears to be one of the more potent and clearly the most A1-selective antagonist reported to date, with K1 values of 0.67 and 0.45 nM, respectively, at the rat and cloned human A1-receptors and with 1800-fold (rat) and 2400-fold (human) subtype selectivity. Both enantiomers, administered intravenously to saline-loaded rats, induced diuresis via antagonism of renal A1-adenosine receptors.     

Hydrothermal syntheses and characterization of three lanthanide coordination complexes constructed by 2,2’:6’,2’’-terpyridine and 2,2’-biphenyldicarboxylic acid

Two 1D coordination polymers [Ln2(dpdc)3(tpy)2·H2O]n [Ln=Nd 1, Yb 2, H2dpdc=2,2’-biphenyldicarboxylic acid and tpy= 2,2’:6’,2’’-terpyridine] and one dinuclear complex Er2(dpdc)2(Hdpdc)2(tpy)2 3 were obtained via hydrothermal reactions and determined by X-ray diffraction analysis. The crystal structure data of 1 and 2 revealed that two coordination polymers were isostructural and possessed a 1D chain framework consisting of eight-coordinated Ln(III) centers. In the asymmetric unit, the two Er(III) ions in 3 were both nine-coordinated and had similar coordination environments. The Er(III) ions were bridged by dpdc2-ligands into dinuclear structures. The complexes were also characterized by IR spectra and thermogravimetric analysis. The solid fluorescence of 1 and 3 was also investigated at room temperature.     

Adenosine A2A receptors modulate the binding characteristics of dopamine D2 receptors in stably cotransfected fibroblast cells

In membrane preparations from rat striatum, where adenosine A2A and dopamine D2 receptors are coexpressed, stimulation of adenosine A2A receptors was found to decrease the affinity of dopamine D2 receptors for dopamine agonists. We now demonstrate the existence of this antagonistic interaction in a fibroblast cell line (Ltk-) stably transfected with the human dopamine D2 (long-form) receptor and the dog adenosine A2A receptor cDNAs (A2A-D2 cells). In A2A-D2 cells, but not in control cells only containing dopamine D2 receptors (D2 cells), the selective adenosine A2A agonist 2-[p-(2-carboxyethyl)-phenethylamino]-5'-N-ethyl-carboxamido adenosine (CGS 21680) induced a 2-3-fold decrease in the affinity of dopamine D2 receptors for dopamine, as shown in competition experiments with dopamine versus the selective dopamine D2 antagonist [3H]raclopride. By contrast, activation of the constitutively expressed adenosine A2B receptors with 5'-N-ethyl-carboxamidoadenosine (NECA) did not modify dopamine D2 receptor binding. In A2A-D2 cells CGS 21680 failed to induce or induced only a small increase in adenosine-3',5'-cyclic-monophosphate (cAMP) accumulation. In D2 cells NECA- or forskolin-induced adenylyl cyclase activation was not associated with any change in dopamine D2 receptor binding. These results indicate that adenylyl cyclase activation is not involved in the adenosine A2A receptor-mediated modulation of the binding characteristics of the dopamine D2 (long-form) receptor.     

Removal of the high-potential [4Fe-4S] center of the beta-subunit from Escherichia coli nitrate reductase. Physiological, biochemical, and EPR characterization of site-directed mutated enzymes

The beta-subunit of the nitrate reductase of Escherichia coli contains four groups of Cys residues (I-IV) which are thought to bind the single [3Fe-4S] center and the three [4Fe-4S] centers. The first or second Cys residue of group I was substituted by site-directed mutagenesis with Ala or Ser. Physiological, biochemical, and EPR studies were performed on the mutated enzymes. With small variations, the properties of these mutant enzymes do not differ from one another. They were found to be as abundant and as stably bound to the membrane as the native enzyme, provided the gamma-subunit was present. Although physiological activity was reduced, it was sufficient to allow growth on nitrate. The study of variations in EPR intensity as a function of the redox potential indicated that these enzymes only contained three iron-sulfur centers instead of the usual four in the native enzyme. Spectral EPR analysis showed that the [4Fe-4S] center of high redox potential (center 1, +80 mV) was missing. The loss of this center did not affect the stable integration of the other three centers. The data presented here are in total contrast to those we have reported for each of the other three centers (centers 2-4), the loss of which was detrimental to the integration of all centers and to the integration of the molybdenum cofactor (Augier et al., in press). Taken together, our results demonstrated that the first and second Cys residues of group I are the ligands of the [4Fe-4S] center (center 1, +80 mV) and that this center participates in electron transfer, but is dispensable. On the basis of these results, it is proposed that the [3Fe-4S] center (center 2, +60 mV) also plays a biological role and that in the native enzyme both high-potential centers, centers 1 and 2, contribute independently and in parallel to the electron transfer to the molybdenum cofactor.     

Symmetric and asymmetric left ventricular hypertrophy in patients with end-stage renal failure on long-term hemodialysis

BACKGROUND: Patients with end-stage renal disease on regular hemodialysis have an increased prevalence of left ventricular (LV) hypertrophy that is associated with morbidity and mortality. Asymmetric septal hypertrophy and impairment of LV outflow can occur in these patients and may contribute to adverse outcomes. More insight into the prevalence, extent, geometry, and promoting factors of LV hypertrophy is important. METHODS: An unselected group of 62 patients (31 women), aged 55 +/- 14 years, on maintenance hemodialysis was investigated by Doppler echocardiography. Eight patients with valvular heart disease were excluded from further analysis. We assessed prevalence of LV hypertrophy and asymmetric septal hypertrophy, as well as parameters of LV geometry and LV filling and outflow dynamics. RESULTS: Prevalence of LV hypertrophy was 65%. Patients were analyzed according to LV mass and geometry. Mean LV mass index was normal (105 +/- 17 g/m2) in Group 1 without LV hypertrophy (n = 19); it was markedly elevated in Group 2 (symmetric hypertrophy, n = 22) and Group 3 (asymmetric hypertrophy with systolic anterior movement of mitral valve, n = 7), and highest (191 +/- 54 g/m2) in Group 4 (asymmetric hypertrophy without systolic anterior movement of mitral valve, n = 6, p < 0.001). Age, body mass index, and duration of hypertension were associated with LV hypertrophy and asymmetric septal hypertrophy (p = 0.01). Group 3 with systolic anterior motion of mitral valve had the smallest end-diastolic LV diameters (p = 0.02); increased heart rates, and increased ejection velocities in the LV outflow tract (p = 0.03, and p = 0.005, respectively, vs. Groups 1, 2, and 4) which pointed to an impairment of LV outflow. CONCLUSIONS: Symmetric LV hypertrophy and asymmetric septal hypertrophy are frequent in patients on maintenance hemodialysis. Predictors for LV hypertrophy were age and body mass index, and, particularly for asymmetric septal hypertrophy, age and hypertension duration. Volume withdrawal during hemodialysis may lead to symptomatic hypotension due to dynamic obstruction in some patients with severe asymmetric septal hypertrophy.     

Pulmonary artery growth after systemic-to-pulmonary shunt in children with a univentricular heart and a hypoplastic pulmonary artery bed. Implications for Fontan surgery

The aim of the study was to investigate the developmental pattern of hypoplastic pulmonary artery (p.a.) bed augmented by systemic-to-pulmonary shunt in children with univentricular heart scheduled for Fontan surgery. For the study, a highly selected patient cohort was chosen (12 patients aged between 5 and 19 years; mean 9.5 years) with comparable initial morphological conditions of univentricular heart and hypoplastic p.a. bed, who after mandatory systemic-to-pulmonary shunt underwent Fontan procedure at time of normalization of pulmonary artery size. Further selection criteria were: normal pulmonary vascular resistance at time of Fontan procedure, competent a-v valve(s), and globally unimpaired ventricular function. All patients were grouped according to the preoperative pulmonary flow index (Qpi; L/min/m2 b.s.a.) measured immediately before Fontan operation: Group A: 1.5-2.5; B: 3.0-4.0; C: 4.0-5.0; D: > 6.0, and their cardio-pulmonary hemodynamic situation (Hb, SAsat%, Qp/Qs, PAP, Rp/Rs, EDVP, FS%, ventricular diastolic compliance (VC = EDVP/Qpi + Qsi) as well as the pulmonary artery size and area using standard (Nakata-index, McGoon-ratio) and a self designed computer assisted planimetric area calculation (PPAAI; cm2/m2 b.s.a.) analysed. Each patient underwent 1-3 shunt procedures, the mean shunt patency period for groups A, B, C and D was 12, 8.6, 5.3, and 4.5 years, respectively. The mean Nakata-index (283, 297, 324, 405 in groups A-D) and the McGoon-ratio (2.0, 2.2, 2.8, 3.3 in groups A-D) correlated with the Qp index, reflecting flow dependent development of pulmonary artery bed. No correlation was found between Qpi and PPAAI (47, 40, 41 and 47 in group A-D). The VC/Qp relation showed an inversely proportional pattern with values 2.3, 1.0, 0.8, 0.7 for corresponding groups A-D, the lowest VC in group A correlated with polyglobulic status (Hb- values; g/dl): 21.3 in A vs 19.8, 18.0 and 16.5 in B-D) and mean arterial SAsat-values (77% in A vs 83%, 84% and 89% in B-D). In conclusion, in our highly selected patient cohort, the development of p.a. size was strongly flow-dependent, and patients with restrictive pulmonary flow needed an approximately threefold longer time period to normalize their p.a. size compared to those with excessive flow. In patients with restrictive pulmonary flow, the Nakata-index underestimated the degree of development of the pulmonary artery system, probably due to the distortion of the proximal p.a. segment. In consequence, in these patients the normalization of the p.a. bed and thus suitability for the Fontan procedure probably occurred much earlier. Based on our observations and those of others, in patients with excessive flow the normalization of p.a. bed, provided it occurs within 3-4 years, seems not necessarily to be associated with a deterioration of ventricular function.     

Wasps are the cause of an increasing mastitis problem in dairy cattle in Israel

The purpose of this study was to estimate if the erythropoietin (EPO) concentration in cord arterial blood can be an indicator of a fetal risk. We studied EPO concentration measured by enzyme immonoassay in ten patient groups: (1) control group with healthy newborns (n = 72); (2) neonates born by elective caesarean section (n = 16); (3) newborns with acidosis at birth (n = 12); (4) newborns with 1-min-Apgar < 7 (n = 8); (5) preterm neonates (n = 25); (6) newborns with gestational age > or = 242 weeks (n = 19); (7) neonates born to mothers with hypertension (n = 16); (8) newborns with signs of fetal distress in CTG (n = 29); (9) neonates born to mothers with diabetes (n = 19), divided into two subgroups: diabetes White A-D (n = 8) and gestational diabetes (n = 11); (10) neonates born to mothers with diabetes White A-D and with acidosis at birth (n = 7). The geometric mean was 26.4 mU/ml in the control group. EPO levels was found significantly increased (p < 0.01) in the following groups: (3) newborns with acidosis (52 mU/ml); (6) newborns with gestational age > or = 242 weeks (63.5 mU/ml); (8) newborns with signs of fetal distress in CTG (47.1 mU/ml); (9) neonates born to mothers with diabetes White A-D (47.7 mU/ml); (10) neonates born to mothers with diabetes White A-D and with acidosis at birth (> 64 mU/ml). We came to the conclusion that the cord arterial EPO concentration indicates a chronic fetal hypoxia and a longer duration of hypoxia before birth.     

E. coli D-glyceraldehyde-3-phosphate dehydrogenase modified by 2,3-butanedione: manifestation of a pairwise of non-equivalence of active centers

Chemical modification of E. coli d-glyceraldehyde-3-phosphate dehydrogenase by an arginine-specific reagent, 2,3-butanedione, stabilized the tetrametric enzyme in an asymmetric state, with only two of the four active centers able to catalyze oxidative phosphorylation of D-glyceraldehyde-3-phosphate. The catalytically incompetent active centers retain the capacity of binding NAD+, forming charge transfer complex, and be alkylated by iodoacetamide. Analogous results have been previously obtained with the rabbit muscle D-glyceraldehyde dehydrogenase modified at a single arginine residue per subunit (Kuzminskaya, E.V., Asryants, R.A., and Nagradova, N.K. (1991) Biochim. Biophys. Acta 1075, 123-130), the only differences being inaccessibility of the catalytically incompetent pair of active centers to the alkylating reagent, on one hand, and lower residual activity exhibited by the functioning active centers (3-4%), on the other. In the case of E. coli enzyme, activity loss upon arginine modification never exceeded 80-82%. These results are consistent with the idea that the two enzymes share common principles of the protein design, but differ in the peculiarities of their active centers conformations. An improved method for D-glyceraldehyde-3-phosphate dehydrogenase purification from a wild type E. coli strain is described.     

Determination of the subunit composition of haptoglobin 2-1 polymers using quantitative densitometry of polyacrylamide gels

Human haptoglobin (Hp), a hemoglobin-binding glycoprotein containing two types of polypeptide chains, alpha and beta, in equimolar amounts linked by disulfide bonds, exists in three major phenotypes determined by the properties of the alpha chain: Hp 1-1 (alpha1), Hp 2-2 (alpha2), and Hp 2-1 (alpha1 and alpha2). Hp 2-2 and Hp 2-1 form a series of alpha-disulfide-linked polymers. The subunit composition of the Hp 2-1 series was studied by isolation of single Hp 2-1 polymers by polyacrylamide gel electrophoresis. After reductive disulfide cleavage and alkylation the relative content of alpha2 and alpha1 polypeptide chains was determined by quantitative densitometry of acid/urea polyacrylamide gels stained with Coomassie brilliant blue R250. The molar ratios alpha2/alpha1 for the Hp 2-1 polymers. P1 through P5 (in order of decreasing electrophoretic mobility), were found to be: P1, 0.0 (alpha1 only); P2, 0.48; P3, 0.97; P4, 1.6; P5, 2.0. Since one alphabeta-Hb half-molecule is known to bind to each Hp beta chain, the beta polypeptide chain content of each of the Hp 2-1 polymers could be estimated by by counting the number of Coomassie blue bands formed after electrophoresis of isolated Hp 2-1 polymers fractionally saturated with cyanmethemoglobin (Hb). The number of beta chains present in Hp 2-1 polymers P1 through P4 was determined to be: P1, 2; P2, 3; P3, 4 and P4, 5. Molecular weights of the Hp 2-1 polymers were determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresus using as standards the almost homologous Hp 2-2 polymer series whose molecular weights are known from ultracentrifugation studies. Molecular weights for the first five Hp 2-1 polymers were estimated to be 107,000; 162,000; 217,000, 274,000; and 331,000, respectively. These data are consistent with the previously proposed model for the subunit composition of the Hp 2-1 polymer series when P1 = (alpha1 beta)2 and the subsequent polymers in order are represented as (alpha1 beta)2(alpha2 beta)n where n = 1,2,3,4...     

Efficient gene transfer to human squamous cell carcinomas by the herpes simplex virus type 1 amplicon vector

We determined the diagnostic value of the EEG in young children with Angelman syndrome (AS) and Rett syndrome (RS). EEGs, recorded before 5 years of age, of 10 patients with AS, 10 with RS and 10 with mental retardation of other origin were studied blindly by two examiners for the presence of the following items: (A) 4-6 Hz rhythmic activity of over 200 microV; (B) 2-3 Hz frontal activity of 200-500 microV; (C) posterior spikes; (D) triphasic frontal waves; (E) central and/or centro-temporal spike-wave complexes; and (F) other epileptic discharges. Based on these items the EEGs were scored as AS (A-D); RS (E-F); or other. Examiners never made a mistake between AS and RS. One examiner labeled 6 of 10 AS cases correctly, the other 5; 4 (5) were characterized as 'other.' In RS cases 5 were labeled as 'other' by the first examiner and 3 by the second one. We conclude that EEG patterns of AS and RS are sufficiently different to help differentiate between AS and RS at a young age, which has a bearing on genetic counseling.     

Studies on 5-lipoxygenase inhibitors. II. Discovery, optical resolution and enantioselective synthesis of FR110302, a highly potent non-redox type 5-lipoxygenase inhibitor

A novel series of 2,2-dialkyl-5-(2-quinolylmethoxy)-1,2,3, 4-tetrahydro-1-naphthols was synthesized and evaluated as 5-lipoxygenase (5-LO) inhibitors. Systematic optimization led to identification of several highly potent non-redox type 5-LO inhibitors with nanomolar IC50s as racemic mixtures. Optical resolution of racemate 50 indicated that its 5-LO inhibitory activity was enantiospecific and due to the (+)-enantiomer. An efficient synthetic route to the (+)-enantiomers via asymmetric reduction of tetralone intermediates was established. The best compound, (+)-2,2-dibutyl-5-(2-quinolylmethoxy)-1,2,3,4-tetrahydro-1-naphtho l (FR110302, (+)-50), showed potent inhibitory activity against leukotriene (LT) biosynthesis by intact neutrophiles in rats (IC50 4.9 nM) and in humans (IC50 40 nM). Furthermore oral administration of FR110302 significantly inhibited neutrophil migration in the rat air pouch model at 1 mg/kg.     

Truncation of macrophage-derived chemokine by CD26/ dipeptidyl-peptidase IV beyond its predicted cleavage site affects chemotactic activity and CC chemokine receptor 4 interaction

The serine protease CD26/dipeptidyl-peptidase IV (CD26/DPP IV) and chemokines are known key players in immunological processes. Surprisingly, CD26/DPP IV not only removed the expected Gly1-Pro2 dipeptide from the NH2 terminus of macrophage-derived chemokine (MDC) but subsequently also the Tyr3-Gly4 dipeptide, generating MDC(5-69). This second cleavage after a Gly residue demonstrated that the substrate specificity of this protease is less restricted than anticipated. The unusual processing of MDC by CD26/DPP IV was confirmed on the synthetic peptides GPYGANMED (MDC(1-9)) and YGANMED (MDC(3-9)). Compared with intact MDC(1-69), CD26/DPP IV-processed MDC(5-69) had reduced chemotactic activity on lymphocytes and monocyte-derived dendritic cells, showed impaired mobilization of intracellular Ca2+ through CC chemokine receptor 4 (CCR4), and was unable to desensitize for MDC-induced Ca2+-responses in CCR4 transfectants. However, MDC(5-69) remained equally chemotactic as intact MDC(1-69) on monocytes. In contrast to the reduced binding to lymphocytes and CCR4 transfectants, MDC(5-69) retained its binding properties to monocytes and its anti-HIV-1 activity. Thus, NH2-terminal truncation of MDC by CD26/DPP IV has profound biological consequences and may be an important regulatory mechanism during the migration of Th2 lymphocytes and dendritic cells to germinal centers and to sites of inflammation.     

Different intestinal permeability patterns in relatives and spouses of patients with Crohn''s disease: an inherited defect in mucosal defence?

The CHCl3 extract of the root of Angelica japonica showed high inhibitory activity against human gastric adenocarcinoma (MK-1) cell growth. From this extract, a new furanocoumarin named japoangelone and four furanocoumarin ethers of falcarindiol, named japoangelols A-D, were isolated together with caffeic acid methyl ester, four polyacetylenic compounds (panaxynol, falcarindiol, 8-O-acetylfalcarindiol, and (9Z)-1,9-heptadecadiene-4,6-diyne-3,8,11-triol), eight coumarins (osthol, isoimperatorin, scopoletin, byakangelicin, xanthotoxin, bergapten, oxypeucedanin methanolate, and oxypeucedanin hydrate), and two chromones (3'-O-acetylhamaudol, and hamaudol). The structures of the new isolates were determined based on spectral evidence. The ED50 of isolates against MK-1, HeLa, and B16F10 cell lines are reported.     

Three acylated saponins and a related compound from Pithecellobium dulce

Four new oleanane-type triterpene glycosides, pithedulosides H-K (1-4), were isolated from the seeds of Pithecellobium dulce. Their structures were established by extensive NMR experiments and chemical methods. Compounds 1-3 comprised acacic acid as the aglycon and either monoterpene carboxylic acid and its xyloside or monoterpene carboxylic acid as the acyl moiety at C-21. The oligosaccharide moieties linked to C-3 and C-28 were determined as alpha-L-arabinopyranosyl-(1-->2)-alpha-L-arabinopyranosyl-(1 -->6)- [beta-D-glucopyranosyl-(1-->2)]-beta-D-glucopyranosyl and alpha-L-arabinofuranosyl-(1-->4)-[beta-D-glucopyranosyl-(1-->3)]-alpha- rhamnopyranosyl-(1-->2)-beta-D-glucopyranosyl ester, respectively. Compound 4 was established as an echinocystic acid 3-O-glycoside having the same sugar sequences as 1-3. Also obtained in this investigation was the known compound 5, which was identified as echinocystic acid 3-O-beta-D-xylopyranosyl- (1-->2)-alpha-L-arabinopyranosyl-(1-->6)-[beta-D-glucopyranosyl-(1 -->2)]- beta-D-glucopyranoside.     

Water transport in perfused scorpion ileum

Water transport in desert scorpion ileum involves two independent transfer pathways operating in parallel: 1) paracellular flow occurs through intercellular spaces in response to transmural osmotic or ionic gradients; and 2) transcellular water transport occurs across apical and basal cell membranes in response to a basal, energy-requiring sodium efflux process. The tissue exhibits no osmotic rectification over the range of transepithelial osmotic gradients imposed (Lp = hydraulic conductivity), Lp = 95 x 10(-7) cm - s-1 - atm-1), but displays apparent asymmetric ion permeability in response to transmural ion gradients, as determined by codiffusional water movements across the preparation. Osmotic permeability ((Pos), Pos = 1.13 x 10(-3) cm - s-1) of the tissue exceeds diffusional permeability ((Pd), Pd = 1.45 x 10(-5) cm - s-1) by almost two orders of magnitude. In the absence of osmotic or hydrostatic pressure gradients, transmural water transport requires cellular metabolism, is sodium-dependent, is inhibited by potassium, and produces an apparent strongly hypotonic absorbate. This water transport process appears to be adaptive, as scorpion dehydration results in alterations of luminal ion concentrations that favor increased net flow of water to the hemolymph.     

Role of Epstein-Barr virus in fine-needle aspirates of metastatic neck nodes in the diagnosis of nasopharyngeal carcinoma

The crystal structure of the peptide Boc-Phe-Val-OMe determined by X-ray diffraction methods is reported in this paper. The crystals grown from aqueous methanol are orthorhombic, space group P2(1)2(1)2(1),a = 11.843(2), b = 21.493(4), c = 26.676(4) A3 and V = 6790 A3. Data were collected on a CAD4 diffractometer using MoK alpha radiation (lambda = 0.7107 A) up to Bragg angle theta = 26 degrees. The structure was solved by direct methods and refined by a least-squares procedure to an R value of 6.8% for 3288 observed reflections. There are three crystal-lographically independent peptide molecules in the asymmetric unit. All the three molecules exhibit extended conformation. The sidechain of the Val2 residue shows two different conformations. The conformation of the peptide Boc-Phe-Val-OMe is compared with the conformation of Ac-delta Phe-Val-OH. It is observed that while Boc-Phe-Val-OMe exhibits an extended conformation, Ac-delta Phe-Val-OH shows a folded conformation. The results of this comparison highlight the conformation constraining property of the delta Phe residue. Interestingly, even though Boc-Phe-Val-OMe and Ac-delta Phe-Val-OH are conformationally different, they exhibit similar packing patterns in the solid state.