Acid Chromatography Research Articles

Quantification of plasticizers in poly(vinyl chloride) commodities by high-performance thin-layer chromatography

Flexible packaging films, lids of glass jars, elastic toys, or medical commodities made of poly(vinyl chloride) contain different plasticizers, which tend to migrate out of the respective product. To test compliance to regulations, the content of plasticizers and their migration properties have to be determined analytically. With a rapid high-performance thin-layer chromatography (HPTLC) method it was able to quantify phthalic acid esters, diisononyl cyclohexane-1,2-dicarboxylate, sebacates, citrates, adipates, and epoxidized soybean oil (ESBO) simultaneously. Chromatography was performed on HPTLC silica gel glass plates, and detection was enabled by dipping the plate into primuline solution. ESBO could be quantified after a newly introduced lipase treatment and chromatography of the epoxidized fatty acids. Validation was performed by analyzing self-made plastisols, showing good recoveries and standard deviations. Limits of detection and quantification generally were approximately 10–20 and 30–60 ng per z...

Potential of chiral anion-exchangers operated in various subcritical fluid chromatography modes for resolution of chiral acids

Anion-exchange-type chiral stationary phases (CSPs) derived from quinine or quinidine were applied in subcritical fluid chromatography (SFC) for the direct separation of chiral acidic compounds. Employing subcritical (sc) mobile phase modes (CO2+methanol as co-solvent and acids and bases as additives) first the influence of type and amount of acidic and basic additives on separation performance was investigated. Secondly, water was tested as a neutral additive and the influence of temperature variation on enantioselectivity was studied. Thirdly, we could chromatographically confirm that the often verbalized “inherent acidity” of sc CO2+methanol is manifested by the in situ formation of methylcarbonic acids in the sc mobile phase and thus functioning as acidic additive. Accordingly the dissociated methylcarbonic acid, acting as a counterion, enables an anion exchange mechanism between the cationic CSP and the corresponding acidic analyte. In the absence of a dissociable acid in the mobile phase such an ion exchange mode would not work following a stoichiometric displacement model. This finding is further corroborated by the use of ammonia in methanol as co-solvent thus generating in situ the ammonium salt of methylcarbonic acid. In summary, we report on ion-exchange mediated chromatographic separations in SFC modes by merely using (i) sc CO2 and MeOH, (ii) sc CO2 and ammonia in MeOH, and (iii) sc CO2 and MeOH plus acids and bases as additives. Comparisons to HPLC mode have been undertaken to evaluate merits and limitations. This mode exhibits high potential for preparative chromatography of chiral acids combining pronounced enantioselectivity with high column loadability and avoiding possibly troublesome mobile phase additives, as the in situ formed methylcarbonic acid disintegrates to CO2 and methanol upon pressure release.

Differences in faecal bacteria populations and faecal bacteria metabolism in healthy adults and celiac disease patients

Differences in the intestinal microbiota between children and adults with celiac disease (CD) have been reported; however, differences between healthy adults and adults with CD have not been clearly demonstrated. The aim of this study was to evaluate the differences in the intestinal microbiota between adults with CD and healthy individuals. Microbial communities in faecal samples were evaluated by PCR-denaturing gradient gel electrophoresis (DGGE) and gas-liquid chromatography of short chain fatty acids (SCFAs). The study group included 10 untreated CD patients, 11 treated CD patients and 11 healthy adults (in normal gluten diet and in GFD). UPGMA clustered the dominant microbial communities of healthy individuals together and separated them from the dominant microbial communities of the untreated CD patients. Most of the dominant microbial communities of the treated CD patients clustered together with those of healthy adults. The treated CD patients showed a reduction in the diversity of Lactobacillus and Bifidobacterium species. The presence of Bifidobacterium bifidum was significantly higher in untreated CD patients than healthy adults. There was a significant difference between untreated CD patients and healthy adults, as well as between treated CD patients and healthy adults, regarding acetic acid, propionic acid, butyric acid, and total SCFAs. healthy adults have a different faecal microbiota from that of untreated CD patients. A portion of the treated CD patients displayed a restored "normal" microbiota. The treated CD patients significantly reduce the Lactobacillus and Bifidobacterium diversity. Healthy adults have a different faecal SCFAs content from that of CD patients.

Williams syndrome (syndrome of idiopathic hypercalcemia)

Williams syndrome was first described in 1961 by J.C.P. Williams et al. The population frequency is 1:7500-10 000 live births; the ratio of boys and girls is about 1:1. The nature of this genetic disease is the loss of genetic material (microdeletion) of the long arm of chromosome 7. During microdeletion the loss of elastin, LIM-kinase-1 and replication factor C2 (RFC) genes occurs, some of the «lost» genes have not yet been identified. A more rare form of the syndrome exhibits deletions on chromosomes 11 and 12 - 11q13-q14, and 22q. Presented was the authors’ clinical observation. A child was born from the second pregnancy (the first one ended in miscarriage at 12 weeks of the term), which had a physiological course, first childbirth was given at the term of 40 weeks, the newborns body weight at birth was 2600 g, body length 49 cm. At 1 year 8 months the baby’s height was 80 cm, body weight was 10 kg 800 g, head circumference - 50 cm, chest circumference - 51 cm. Multiple stigmas of dysembryogenesis were present. The head was irregularly shaped, the large fontanelle was closed. A marked face dysmorphism: a broad forehead, the unusual shape of the eyes with swelling around them, epicanthal fold, drooping full cheeks, the characteristic shape of the nose with a rounded blunt end and anteriorly open nostrils, a small pointed chin, a large open mouth, full lips, especially the lower one, progeny, small teeth, jagged, and affected by caries. The thorax was narrow, a depressed sternum in the form of a «сobbler’s chest». The muscle tone was moderately reduced. The psychomotor development at the level of a 8-9 months old. Cardiologist’s conclusion: a congenital heart defect, hypoplasia of the isthmus of the aortic arch. Conclusion of the geneticist: multiple stigmas of dysembryogenesis, a characteristic phenotype. Karyological analysis 46,XY - without karyotype abnormalities. Chromatography of the amino acids - without any pathology. Diagnosis: Williams syndrome. Diagnosis of Williams syndrome sometimes possesses known difficulties. The described clinical case illustrates the possibilities of diagnosing the syndrome, based primarily on a careful analysis of the medical history, of the clinical picture and physical examination.

Critical Comparison of Multidimensional Separation Methods for Increasing Protein Expression Coverage

We present a comparison of two-dimensional separation methods and how they affect the degree of coverage of protein expression in complex mixtures. We investigated the relative merits of various protein and peptide separations prior to acidic reversed-phase chromatography directly coupled to an ion trap mass spectrometer. The first dimensions investigated were density gradient organelle fractionation of cell extracts, 1D SDS-PAGE protein separation followed by digestion by trypsin or GluC proteases, strong cation exchange chromatography, and off-gel isoelectric focusing of tryptic peptides. The number of fractions from each first dimension and the total data accumulation RP-HPLC-MS/MS time was kept constant and the experiments were run in triplicate. We find that the most critical parameters are the data accumulation time, which defines the level of under-sampling and the avoidance of peptides from high expression level proteins eluting over the entire gradient.

Highly sensitive chiral analysis in capillary electrophoresis with large-volume sample stacking with an electroosmotic flow pump

To improve the sensitivity in chiral analysis by capillary electrophoresis without loss of optical resolution, application of large-volume sample stacking with an electroosmotic flow pump (LVSEP) was investigated. Effects of the addition of cyclodextrin (CD) into a running solution on the LVSEP preconcentration was theoretically studied, where the preconcentration efficiency and effective separation length would be slightly increased if the effective electrophoretic velocity (vep,eff,BGS) of the analytes was decreased by interacting with CD. In LVSEP-CD-modified capillary zone electrophoresis (CDCZE) and LVSEP-CD electrokinetic chromatography with reduced vep,eff,BGS, up to 1000-fold sensitivity increases were achieved with almost no loss of resolution. In LVSEP-CD-modified micellar electrokinetic chromatography of amino acids with increased vep,eff,BGS, a 1300-fold sensitivity increase was achieved without much loss of resolution, indicating the versatile applicability of LVSEP to many separation modes. An enantio-excess (EE) assay was also carried out in LVSEP-CDCZE, resulting in successful analyses of up to 99.6% EE. Finally, we analyzed ibuprofen in urine by desalting with a C18 solid-phase extraction column. As a typical result, 250ppb ibuprofen was well concentrated and optically resolved with 84.0–86.6% recovery in LVSEP-CDCZE, indicating the applicability of LVSEP to real samples containing a large amount of unnecessary background salts.

Primary fatty acid amide metabolism: conversion of fatty acids and an ethanolamine in N18TG2 and SCP cells

Primary fatty acid amides (PFAM) are important signaling molecules in the mammalian nervous system, binding to many drug receptors and demonstrating control over sleep, locomotion, angiogenesis, and many other processes. Oleamide is the best-studied of the primary fatty acid amides, whereas the other known PFAMs are significantly less studied. Herein, quantitative assays were used to examine the endogenous amounts of a panel of PFAMs, as well as the amounts produced after incubation of mouse neuroblastoma N(18)TG(2) and sheep choroid plexus (SCP) cells with the corresponding fatty acids or N-tridecanoylethanolamine. Although five endogenous primary amides were discovered in the N(18)TG(2) and SCP cells, a different pattern of relative amounts were found between the two cell lines. Higher amounts of primary amides were found in SCP cells, and the conversion of N-tridecanoylethanolamine to tridecanamide was observed in the two cell lines. The data reported here show that the N(18)TG(2) and SCP cells are excellent model systems for the study of PFAM metabolism. Furthermore, the data support a role for the N-acylethanolamines as precursors for the PFAMs and provide valuable new kinetic results useful in modeling the metabolic flux through the pathways for PFAM biosynthesis and degradation.

Ionic Liquids in Reversed-Phase High-Performance Liquid Chromatography of Phenolic Acids on Different Stationary Phases

Phenolic acids belonging to weak acidic compounds were analyzed in the reversed phase system, modified with the addition of ionic liquids: 1-butyl-3-methyl-imidazolium hexafluorophosphate (BMIM PF6) and 1-butyl-3-methyl-imidazolium chloride (BMIM Cl) on three different columns: Zorbax Extend-C18, Zorbax SB-Phenyl, and Zorbax SB-CN in acidic conditions. The effect of the concentration, the type of different ionic liquids, and the type of organic solvent on the analytes retention were examined on chosen stationary phases. It was established that the biggest changes of the retention factor of undissociated analytes were associated with addition of ionic liquid having the asymmetric cation enlarged with hydrophobic substituents possessing chaotropic properties and neutral anions. The retention mechanism was analyzed on the basis of k vs. ionic liquid concentration in aqueous-organic mobile phase with a constant amount of phosphate buffer.

Gas Chromatographic Separation of Docosenoic Acid Positional Isomers on an SLB-IL100 Ionic Liquid Column

Gas chromatography (GC) of docosenoic acid (22:1) has been performed for the separation of positional isomers on the novel SLB-IL100 column with a highly polar ionic liquid stationary phase. A test mixture of 22:1 methyl esters prepared from total lipids of flounder was subjected to GC on a 60 m×0.32 mm i.d. column at an isothermal temperature of 150°C-180°C. On this column, all five positional isomers separated in the elution order of 22:1n-15, 22:1n-13, 22:1n-11, 22:1n-9, and 22:1n-7. The positional isomers, 22:1n-15, 22:1n-13, and 22:1n-11, unresolvable on conventional polar polymer phase columns, were almost completely separated from each other within 24 min at 170°C. The equivalent chain length values of 22:1n-11 to 22:1n-7 were parallel to those on polyethylene glycol and cyanopropyl polysiloxane columns, whereas 22:1n-15 and 22:1n-13 were relatively lower and closer to saturated 22:0 acid. Similar findings were also obtained for co-injected 20:1n-15 to 20:1n-11 isomers. Analysis of fish 22:1 revealed that 22:1n-13 is not always a minor isomer, as previously reported for several samples. The results of this study confirm the view that SLB-IL100 is a powerful tool for GC analysis of monounsaturated fatty acids.

Involvement of bacterial TonB-dependent signaling in the generation of an oligogalacturonide damage-associated molecular pattern from plant cell walls exposed to Xanthomonas campestris pv. campestris pectate lyases

BackgroundEfficient perception of attacking pathogens is essential for plants. Plant defense is evoked by molecules termed elicitors. Endogenous elicitors or damage-associated molecular patterns (DAMPs) originate from plant materials upon injury or pathogen activity. While there are comparably well-characterized examples for DAMPs, often oligogalacturonides (OGAs), generated by the activity of fungal pathogens, endogenous elicitors evoked by bacterial pathogens have been rarely described. In particular, the signal perception and transduction processes involved in DAMP generation are poorly characterized.ResultsA mutant strain of the phytopathogenic bacterium Xanthomonas campestris pv. campestris deficient in exbD2, which encodes a component of its unusual elaborate TonB system, had impaired pectate lyase activity and caused no visible symptoms for defense on the non-host plant pepper (Capsicum annuum). A co-incubation of X. campestris pv. campestris with isolated cell wall material from C. annuum led to the release of compounds which induced an oxidative burst in cell suspension cultures of the non-host plant. Lipopolysaccharides and proteins were ruled out as elicitors by polymyxin B and heat treatment, respectively. After hydrolysis with trifluoroacetic acid and subsequent HPAE chromatography, the elicitor preparation contained galacturonic acid, the monosaccharide constituent of pectate. OGAs were isolated from this crude elicitor preparation by HPAEC and tested for their biological activity. While small OGAs were unable to induce an oxidative burst, the elicitor activity in cell suspension cultures of the non-host plants tobacco and pepper increased with the degree of polymerization (DP). Maximal elicitor activity was observed for DPs exceeding 8. In contrast to the X. campestris pv. campestris wild type B100, the exbD2 mutant was unable to generate elicitor activity from plant cell wall material or from pectin.ConclusionsTo our knowledge, this is the second report on a DAMP generated by bacterial features. The generation of the OGA elicitor is embedded in a complex exchange of signals within the framework of the plant-microbe interaction of C. annuum and X. campestris pv. campestris. The bacterial TonB-system is essential for the substrate-induced generation of extracellular pectate lyase activity. This is the first demonstration that a TonB-system is involved in bacterial trans-envelope signaling in the context of a pathogenic interaction with a plant.

Effect of surface chemistry of carbon sorbents on high-performance liquid chromatography and mass-spectrometric analysis of amino acids

The work shows a complex approach to analyzing amino acids using carbon sorbents with different surface areas, including molecular-statistical calculations, high-performance liquid chromatography, and mass spectrometry with matrix-activated and surface-activated laser desorption/ionization (MALDI, SALDI). An analysis of the thermodynamic adsorption characteristics (TACs) of a series of proteinogenic amino acids and their isomers on graphitized thermal carbon black (GTCB) is carried out. A satisfactory correlation is established between experimental characteristics of amino-acid retention on the Hypercarb carbon sorbent and TACs of these particles calculated using the molecular statistics method. It is found in the identification of amino acids using the MALDI method in the chromato-mass-spectrometric modification in the off-line mode that the application of carbon sorbents as a support results in an increase in the intensity of the registered protonated molecular ions and adducts with alkali cations compared to a conventional experimental technique on a stainless-steel surface.

Characterization of a recombinant aryl β-glucosidase from Neosartorya fischeri NRRL181

An isolated gene from Neosartorya fischeri NRRL181 encoding a β-glucosidase (BGL) was cloned, and its nucleotide sequence was determined. DNA sequence analysis revealed an open reading frame of 1,467bp, capable of encoding a polypeptide of 488 amino acid residues. The gene was over-expressed in Escherichia coli, and the protein was purified using nickel-nitrilotriacetic acid chromatography. The purified recombinant BGL showed a high level of catalytic activity, with V (max) of 886μmolmin(-1)mg-protein(-1) and a K (m) of 68mM for p-nitrophenyl-β-D: -glucopyranoside (pNPG). The optimal temperature for enzyme activity was about 40°C, and the optimal pH was about 6.0. A homology model of N. fischeri BGL1 was constructed based on the X-ray crystal structure of Phanerochaete chrysosporium BGLA. Molecular dynamics simulation studies of the enzyme with the pNPG and cellobiose shed light on the unique substrate specificity of N. fischeri BGL1 only towards pNPG.

Reference intervals for orotic acid in urine, plasma and dried blood spot using hydrophilic interaction liquid chromatography–tandem mass spectrometry

Orotic acid (OA), a marker of hereditary orotic aciduria, is usually used for the differential diagnosis of some hyperammonemic inherited defects of urea cycle and of basic amino acid transporters. This study was aimed to establish age related reference intervals of OA in urine, and for the first time in plasma, and dried blood spot (DBS) from 229 apparently healthy subjects aged from three days to 40 years. The quantification of OA was performed by a previously implemented method, using a stable isotope dilution with 1,3-[15N2]-orotic acid and hydrophilic interaction liquid chromatography–tandem mass spectrometry (HILIC–MS/MS). The method has proved to be sensitive and accurate for a quantitative analysis of OA also in DBS and plasma. According to previous studies, urinary OA levels (mmol/mol of creatinine) decrease significantly with age. The upper limits (as 99th %ile) were of 3.44 and 1.30 in groups aged from three days to 1 year (group 1) and from 1 year to 12 years (group 2), respectively; in teenagers (from 13 to 19 years; group 3) and adults (from 20 to 40 years; group 4) urinary levels became more stable and the upper limits were of 0.64 and 1.21, respectively. Furthermore, OA levels in DBS (μM) also resulted significantly higher in subjects of group 1 (upper limit of 0.89) than in subjects of groups 2, 3 and 4 (upper limits of 0.24, 0.21, and 0.29, respectively). OA levels in plasma (μM) were significantly lower in subjects of group 3 (upper limit of 0.30) than in subjects of groups 1, 2, and 4 (upper limits of 0.59, 0.48, and 0.77, respectively). This method was also employed for OA quantification in plasma and DBS of 17 newborns affected by urea cycle defects, resulting sensitive and specific enough to screen these disorders.

Intracellular Erythrocyte Platelet-activating Factor Acetylhydrolase I Inactivates Aspirin in Blood

Aspirin (acetylsalicylic acid) prophylaxis suppresses major adverse cardiovascular events, but its rapid turnover limits inhibition of platelet cyclooxygenase activity and thrombosis. Despite its importance, the identity of the enzyme(s) that hydrolyzes the acetyl residue of circulating aspirin, which must be an existing enzyme, remains unknown. We find that circulating aspirin was extensively hydrolyzed within erythrocytes, and chromatography indicated these cells contained a single hydrolytic activity. Purification by over 1400-fold and sequencing identified the PAFAH1B2 and PAFAH1B3 subunits of type I platelet-activating factor (PAF) acetylhydrolase, a phospholipase A(2) with selectivity for acetyl residues of PAF, as a candidate for aspirin acetylhydrolase. Western blotting showed that catalytic PAFAH1B2 and PAFAH1B3 subunits of the type I enzyme co-migrated with purified erythrocyte aspirin hydrolytic activity. Recombinant PAFAH1B2, but not its family member plasma PAF acetylhydrolase, hydrolyzed aspirin, and PAF competitively inhibited aspirin hydrolysis by purified or recombinant erythrocyte enzymes. Aspirin was hydrolyzed by HEK cells transfected with PAFAH1B2 or PAFAH1B3, and the competitive type I PAF acetylhydrolase inhibitor NaF reduced erythrocyte hydrolysis of aspirin. Exposing aspirin to erythrocytes blocked its ability to inhibit thromboxane A(2) synthesis and platelet aggregation. Not all individuals or populations are equally protected by aspirin prophylaxis, the phenomenon of aspirin resistance, and erythrocyte hydrolysis of aspirin varied 3-fold among individuals, which correlated with PAFAH1B2 and not PAFAH1B3. We conclude that intracellular type I PAF acetylhydrolase is the major aspirin hydrolase of human blood.

Polyphosphate Deficiency Affects the Sliding Motility and Biofilm Formation of Mycobacterium smegmatis

Inorganic polyphosphate (polyP) is a ubiquitous linear polymer of hundreds of orthophosphate (Pi) residues linked by ATP-like, high-energy, phosphoanhydride bonds. The gene Rv1026 in Mycobacterium tuberculosis encodes a putative exopolyphosphatase which progressively hydrolyzes the terminal residues of polyP to liberate Pi. Rv1026 was cloned into the expressive plasmid pMV261. The resulting plasmid pRv1026 and the plasmid pMV261 were transformed into M. smegmatis strain mc(2)155 by electroporation. The recombinant M. smegmatis (pRv1026) showed relatively decreased polyP concentration and a phenotype different from the M. smegmatis (pMV261) in sliding motility and biofilm formation. The surfactant Tween 80 can enhance this effect on the sliding motility and biofilm formation of M. smegmatis. There are four different peaks between the gas chromatography of cellular wall fatty acid of the M. smegmatis (pRv1026) and the M. smegmatis (pMV261). These results indicate that polyP deficiency can affect the fatty acid composition of cellular wall and these alteration of cell wall might elucidate the reductive ability of strains to slide and form biofilm. This investigation provides novel recognition about the role of Rv1026, which provides novel clues for further study on the physiological role of Rv1026 in M. tuberculosis.

Lectin Domains of Polypeptide GalNAc Transferases Exhibit Glycopeptide Binding Specificity

UDP-GalNAc:polypeptide α-N-acetylgalactosaminyltransferases (GalNAc-Ts) constitute a family of up to 20 transferases that initiate mucin-type O-glycosylation. The transferases are structurally composed of catalytic and lectin domains. Two modes have been identified for the selection of glycosylation sites by GalNAc-Ts: confined sequence recognition by the catalytic domain alone, and concerted recognition of acceptor sites and adjacent GalNAc-glycosylated sites by the catalytic and lectin domains, respectively. Thus far, only the catalytic domain has been shown to have peptide sequence specificity, whereas the primary function of the lectin domain is to increase affinity to previously glycosylated substrates. Whether the lectin domain also has peptide sequence selectivity has remained unclear. Using a glycopeptide array with a library of synthetic and recombinant glycopeptides based on sequences of mucins MUC1, MUC2, MUC4, MUC5AC, MUC6, and MUC7 as well as a random glycopeptide bead library, we examined the binding properties of four different lectin domains. The lectin domains of GalNAc-T1, -T2, -T3, and -T4 bound different subsets of small glycopeptides. These results indicate an additional level of complexity in the initiation step of O-glycosylation by GalNAc-Ts.

Anti-biofilm potential of a glycolipid surfactant produced by a tropical marine strain of Serratia marcescens

A tropical marine bacterium isolated from the hard coral, Symphyllia sp. was identified as Serratia marcescens on the basis of morphological, biochemical and 16S rDNA analysis. The bacterium showed antimicrobial activity towards the pathogens Candida albicans and Pseudomonas aeruginosa and the marine biofouling bacterium Bacillus pumilus. S. marcescens displayed biosurfactant activity as evidenced by drop collapse, blood hemolysis and surface tension reduction (52.0–27 mN m−1). The active compound was purified by solvent extraction and silicic acid chromatography. Characterization was by thin layer chromatography, gas chromatography mass spectroscopy (GC-MS), Fourier transform infrared (FTIR) spectroscopy and 1H as well as 13C nuclear magnetic resonance (NMR) analysis. The surfactant was found to be a glycolipid composed of glucose and palmitic acid. The glycolipid prevented adhesion of C. albicans BH, P. aeruginosa PAO1 and B. pumilus TiO1. The glycolipid also disrupted preformed biofilms of these cultures in microtitre plates. Confocal laser scanning microscopy and electron microscopy confirmed the effective removal of biofilms from glass surfaces. The glycolipid derived from S. marcescens could thus serve as a potential anti-biofilm agent.

Use of a Polystyrene-divinylbenzene-based Weakly Acidic Cation-Exchange Resin Column and Propionic Acid as an Eluent in Ion-Exclusion/Adsorption Chromatography of Aliphatic Carboxylic Acids and Ethanol in Food Samples

We developed an ion-exclusion/adsorption chromatography (IEAC) method employing a polystyrene-divinylbenzene-based weakly acidic cation-exchange resin (PS-WCX) column with propionic acid as the eluent for the simultaneous determination of multivalent aliphatic carboxylic acids and ethanol in food samples. The PS-WCX column well resolved mono-, di-, and trivalent carboxylic acids in the acidic eluent. Propionic acid as the eluent gave a higher signal-to-noise ratio, and enabled sensitive conductimetric detection of analyte acids. We found the optimal separation condition to be the combination of a PS-WCX column and 20-mM propionic acid. Practical applicability of the developed method was confirmed by using a short precolumn with a strongly acidic cation-exchange resin in the H(+)-form connected before the separation column; this was to remove cations from food samples by converting them to hydrogen ions. Consequently, common carboxylic acids and ethanol in beer, wine, and soy sauce were successfully separated by the developed method.

Chemical Trapping of the Dynamic MutS-MutL Complex Formed in DNA Mismatch Repair in Escherichia coli

The ternary complex comprising MutS, MutL, and DNA is a key intermediate in DNA mismatch repair. We used chemical cross-linking and fluorescence resonance energy transfer (FRET) to study the interaction between MutS and MutL and to shed light onto the structure of this complex. Via chemical cross-linking, we could stabilize this dynamic complex and identify the structural features of key events in DNA mismatch repair. We could show that in the complex between MutS and MutL the mismatch-binding and connector domains of MutS are in proximity to the N-terminal ATPase domain of MutL. The DNA- and nucleotide-dependent complex formation could be monitored by FRET using single cysteine variants labeled in the connector domain of MutS and the transducer domain of MutL, respectively. In addition, we could trap MutS after an ATP-induced conformational change by an intramolecular cross-link between Cys-93 of the mismatch-binding domain and Cys-239 of the connector domain.

Arginase Deficiency Presenting as Intractable Hiccups With Severe Hyperammonemia at One Month of Age

Arginase deficiency is a rare urea cycle disorder and generally presents in children of preschool age with developmental delay and spasticity. Unlikely other urea cycle defects, patients rarely present hyperammonemic symptoms, especially in the early infantile period. A one-month-old male infant was admitted to our hospital because of abnormal respiratory condition with persistent hiccups and lethargy. The initial laboratory studies showed respiratory alkalosis and remarkable hyperammonemia [ammonia, 1970 ? mol/L (25 times normal)]. Amino acid chromatography showed a markedly elevated plasma arginine level (1131 µ mol/L; 10 times normal), and erythrocyte arginase activity was undetectable. Despite prompt diagnosis and normalization of ammonia and arginine levels by peritoneal dialysis, the patient developed neurodevelopmental impairment during the one-year follow-up period. In summary, this is a rare case of arginase deficiency in terms of early infantile onset and presentation of the severe form of hyperammone mia. Pathologic hiccups could be one of the clinical clues to the presence of hyperammonemia even in young infants with arginase deficiency. doi:10.4021/jmc141w