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Demonstrating formation of potentially persistent transformation products from the herbicides bromoxynil and ioxynil using liquid chromatography-tandem mass spectrometry (LC-MS/MS).

It is shown that potentially persistent transformation products can be formed from the herbicides bromoxynil (3,5-dibromo-4-hydroxybenzonitrile) and ioxynil (3,5-diiodo-4-hydroxybenzonitrile), and possible leaching to groundwater is discussed. A similar process to the formation of BAM (2,6-dichlorobenzamide) from the herbicide dichlobenil (2,6-dichlorobenzonitrile) can be anticipated as bromoxynil and ioxynil are analogues of dichlobenil and they are degraded by the enzymes nitrilase, nitrile hydratase and amidase. A biodegradation study using cultured Variovorax sp. DSM 11402, a species commonly found in soil, demonstrated that ioxynil and bromoxynil were fully transformed into their corresponding amides in 2-5 days. These amides were not further degraded within 18 days, and formation of other degradation products was not observed. These results are in agreement with biodegradation experiments with dichlobenil. In soil, dichlobenil is transformed into its only observed degradation product BAM, which is persistent and mobile, and has been found in 19% of 5000 samples of Danish groundwater. Variovorax sp. is known to degrade the non-halogenated analogue benzamide, suggesting that degradation of the three amides may be hindered by the halogenated substituents (meta-Br; meta-I; ortho-Cl). This hypothesis is supported by QSAR modelling of fundamental properties. Using a new optimised liquid chromatography-tandem mass spectrometry (LC-MS/MS) method, the sorption and desorption properties of bromoxynil and ioxynil were characterised in sandy topsoil at four concentration levels. The estimated sorption coefficient K(d) was 1.4 L kg(-1) for bromoxynil and 5.4 L kg(-1) for ioxynil, indicating weak to moderate sorption to topsoil. Desorption of the herbicides showed that they were strongly and irreversible bound to the soil (K(des) > K(d)). The amount of herbicide desorbed depended on the initial concentration level. At low levels, K(des) values were higher, indicating stronger binding than at higher levels. The isocratic LC-MS/MS method developed for simultaneous detection of bromoxynil, ioxynil and their main degradation products is described. Using negative electrospray ionisation (ESI-), the detection limits were 0.4-1.0 microg L(-1), with relative standard deviations of 4-10% (n = 10) using direct injection without clean-up steps. The standard curves showed linearity in the range 5-100 microg L(-1) with r(2) > 0.992.

Adsorption↗

Mass spectrometric identification of N-phenyllinoleamide metabolites in mouse peritoneal macrophages.

N-Phenyllinoleamide (NPLA), the anilide of linoleic acid, has been regarded as a marker of the case oils associated with toxic oil syndrome, but the mechanisms of toxic injury remain enigmatic. Experimental data have related an increased systemic toxic effect of heated linoleic anilides to chemical structural modifications that might also be possible by in vivo metabolism; however, little is known about their metabolism. Taking into account that NPLA is a derivative of linoleic acid, a fatty acid that can be metabolized by lipoxygenase activity to a vast array of derivatives possessing biological activity, the objective has been to elucidate the oxidative metabolism of NPLA by mouse peritoneal macrophages, a cellular model with high lipoxygenase activity. Cells were incubated with 0.1 mM NPLA spiked with N-phenyl[1-14C]linoleamide. The metabolites were separated by high-performance liquid chromatography and individually collected prior to GC/MS analysis. Identification of trihydroxy-, monohydroxy- and epoxy-derivatives of NPLA, suggests that this xenobiotic can be metabolized via the same oxidative processes as for linoleic acid. Furthermore, identification of the non-amidated monohydroxylated and trihydroxylated derivatives of linoleic acid arising from NPLA suggests an amidase-like activity with release of aniline and the free fatty acid. These results provide information about possible biological structures arising from NPLA, and open the way to evaluate the biological significance of these metabolites in the inflammatory reactions associated with toxic oil syndrome.

Anilides↗

Molecular cloning and sequence analysis of Flavobacterium meningosepticum glycosylasparaginase: a single gene encodes the alpha and beta subunits.

A full-length insert for the Flavobacterium meningosepticum N4-(N-acetyl-beta-glucosaminyl)-L-asparagine amidase gene was located on a 2500-bp HindIII fragment and cloned into the plasmid vector pBluescript. DNA sequencing revealed an open reading frame of 1020 nucleotides encoding a putative 45-amino-acid leader sequence and a deduced precursor polypeptide of 295 amino acids. In F. meningosepticum this precursor polypeptide undergoes proteolytic processing by an as yet unknown mechanism to generate an alpha-subunit and a beta-subunit, which constitute the active form of the heterodimeric mature glycosylasparaginase. The Flavobacterium glycosylasparaginase gene was expressed in Escherichia coli and found to be enzymatically active. The recombinant enzyme was purified from crude lysates and shown by sodium dodecyl sulfate-polyacrylamide gel electrophoresis to consist of the typical alpha- and beta-subunits. The recombinant beta-subunit cross-reacted to antibody specific for the rat liver beta-subunit, and Edman analysis demonstrated that its amino-terminus corresponded exactly to that of the mature native glycosylasparagine beta-subunit. A comparison of the Flavobacterium glycosylasparaginase with a mammalian glycosylasparaginase revealed 30% structural identity and 60% overall similarity between the prokaryotic and eukaryotic forms of the enzyme. Even more striking was the conservation of the amino acid sequence in both proteins where the post-translational cleavage to generate the active enzyme occurs. Our data demonstrate that deglycosylation of asparagine-linked glycans via hydrolysis of the AspNHGlcNAc linkage is an important reaction which has been preserved during evolution.

Amino Acid Sequence↗

Glycosylation and phosphorylation of lysosomal glycosylasparaginase.

Glycosylasparaginase (EC 3.5.1.26) is a lysosomal amidase which hydrolyzes the bond between asparagine and the sugar moiety in N-linked glycoproteins. Deficiency of the enzyme results in aspartylglycosaminuria (AGU), the most common disorder of glycoprotein degradation. Mature enzyme is formed by two proteolytic cleavage steps subsequent to removal of its signal peptide: (1) an activation cleavage in the ER of the initial single-chain 49-kDa polypeptide into a 27-kDa alpha- and 19-kDa beta-subunit; (2) a cleavage in lysosomes which removes 10 amino acids from the C-terminus of the alpha-subunit without affecting enzyme activity. Each subunit of glycosylasparaginase contains one N-linked oligosaccharide (N38, alpha-subunit; N308, beta-subunit). Both oligosaccharides were phosphorylated and releasable by Endo-H digestion, indicating they were of the high-mannose type. These glycosylation sequenons were mutagenized to determine the role of the oligosaccharide at each site in proper folding and transport of glycosylasparaginase. An N38D mutant underwent the lysosomal processing step, indicating that targeting to lysosomes can be via the phosphorylated beta-subunit oligosaccharide alone. Deletion of the beta-subunit oligosaccharide oat N308 by an aspartic acid substitution resulted in very little protein or enzyme activity in the transfected cells, reemphasizing that glycosylation of the beta-subunit site is important for efficient folding and/or targeting. A different mutation to eliminate the same N-glycosylation sequenon (T310A) yielded more protein and enzyme activity, and a double mutant N38D/T310A yielded the same results as the single beta-subunit substitution. Yield of enzyme for all mutants was increased in cells treated with brefeldin A. The N308 glycosylation site of the beta-subunit appears to be more important in maintaining normal transport and stability of human glycosylasparaginase.

Animals↗

Cloning, sequencing, and expression of Arthrobacter protophormiae endo-beta-N-acetylglucosaminidase in Escherichia coli.

The gene encoding endo-beta-N-acetylglucosaminidase from Arthrobacter protophormiae (Endo-A) was cloned, and its nucleotide sequence was determined. A single open reading frame consisting of 1935 base pairs and encoding a polypeptide composed of signal peptides of 24 amino acids and a mature protein of 621 amino acids was found. The primary structure of Endo-A exhibited significant homology with FO1F.10 gene product from Caenorhabditis elegans and weak homology with peptide-N4-(N-acetyl-beta-D-glucosaminyl)asparagine amidase from Flavobacterium meningosepticum and chitinase from Streptomyces olivaceoviridis. However, the enzyme had no significant homology with any previously reported endo-beta-N-acetylglucosaminidases. Transformed Escherichia coli cells carrying the 4.5-kb fragment expressed Endo-A activity. This enzyme activity was detected in the medium as well as in the periplasmic space of cells under the control of the Endo-A gene promoter. The recombinant Endo-A was efficiently isolated from the periplasmic space of the cells. N-terminal sequence analysis revealed that native and recombinant Endo-A have the same N-terminus. Recombinant and native Endo-A also showed very similar optimum pH profiles and transglycosylation activity.

Amino Acid Sequence↗

Enzymatic modeling of the oligosaccharide chains of glycoproteins immobilized onto polystyrene surfaces.

A method for the modification of the oligosaccharide moiety of even small amounts of purified glycoproteins by enzymatic glycosylation and deglycosylation is described. The method includes noncovalent immobilization of the glycoproteins onto the polystyrene surface of the wells of microtiter plates used as reaction tubes, deglycosylation or glycosylation by incubation either with exoglycosidases or endoglycosidases or with glycosyltransferases, and the characterization of the modified glycan structures by probing them with lectins. Placental transferrin receptor employed as a model glycoprotein was modified in amounts of as little as 100 ng removing sialic acid residues, hybrid-type glycans or all types of N-glycans with neuraminidase, endo-beta-N-acetylglucosaminidase H or peptide-N4-(acetyl-beta-glucosaminyl) asparagine amidase. Asialotransferrin receptor was alpha-2,6-sialylated with alpha-2,6-sialyltransferase from rat liver, but could not be alpha-2,3-sialylated with alpha-2,3-sialyltransferase from porcine liver. Changes in the structure and in the relative amount of the oligosaccharides could be monitored semiquantitatively with high sensitivity by the binding of digoxigenin-labeled lectins and anti-digoxigenin Fab fragments. The method is easy to use, does not require immobilization of the enzymes employed, offers simple separation of the enzymes and the product, and leaves the protein intact for further studies.

Animals↗

Mild chemical deglycosylation of horseradish peroxidase yields a fully active, homogeneous enzyme.

Horseradish peroxidase isoenzyme C (HRP) contains eight N-linked glycans composed of Man, Xyl, Fuc, and GlcNAc. These glycans were resistant to enzymatic hydrolysis by endoglycosidases peptide-N4-(N-acetyl-beta-glucosaminyl) asparagine amidase F, endo-beta-N-acetyl-glucosaminidase H, and endo-beta-N-acetylglucosaminidase F under conditions where ovalbumin was deglycosylated. However, using anhydrous trifluoromethanesulfonic acid (TFMS) in the presence of 90 mM phenol for 5 min at--10 degrees C, all carbohydrate except GlcNAc was removed. Sixty percent of deglycosylated HRP was active after this TFMS treatment. Benzhydroxamic acid affinity chromatography separated active and inactive deglycosylated HRP. TFMS treatment, however, introduced negative charges in all inactive HRP and in about 90% of the active deglycosylated HRP. The nature of this modification has not been identified. After ion-exchange chromatography, homogeneous and fully active deglycosylated HRP, showing the original pI of 9, electronic absorption spectrum, and enzyme kinetics, was obtained, In this purified product no amino acid modifications were detected by amino acid analysis, partial sequencing, and mass spectrometry of tryptic peptides. The deglycosylated product showed greatly reduced solubility in salt solution compared to that of authentic HRP.

Enzyme Activation↗

Selective organic precipitation/extraction of released N-glycans following large-scale enzymatic deglycosylation of glycoproteins.

A major difficulty with isolating enzymatically or chemically released oligosaccharides from large-scale glycoprotein deglycosylation reactions is the time-consuming chromatography, desalting, and concentration steps required to prepare a glycan fraction of manageable proportions. To overcome these time and preparative chromatography equipment requirements, we have developed a rapid organic solvent precipitation/extraction procedure that allows sequential isolation of endo-beta-N-acetylglucosaminidase H (EC 3.2.1.96)-released high-mannose and hybrid, peptide-N(4)-(N-acetyl-beta-glucosaminyl) Asn amidase (EC 3.5.1. 52)-released complex, and beta-eliminated O-linked glycans without the need for intermediate chromatography, desalting, or concentration steps. The method involves precipitation of protein and released glycans at -20 degrees C in 80% acetone and extraction of the glycans from the pellet with 60% aqueous methanol after each deglycosylation step. Three pools of essentially salt- and detergent-free oligosaccharides (high-mannose/hybrid, complex, and O-linked) can be isolated in a high yield in 4 days with this protocol, which has been extensively tested using bovine RNase B, human bile salt-stimulated lipase expressed in Pichia pastoris, hen ovalbumin, bovine fetuin, bovine thyroglobulin, and several invertase preparations from wild-type and mutant yeast strains.

Animals↗

Enzymatic synthesis of the N-glycosidic bond by beta-aspartylation of glycosylamines.

Glycosylasparaginase (EC 3.5.1.26) is an amidase, which cleaves the N-glycosidic linkage during glycoprotein degradation leading to the liberation of L-aspartic acid from various glycoasparagines. In this work we demonstrate that glycosylasparaginase is also capable of catalyzing the synthesis of the N-glycosidic bond by N-beta-aspartylation of beta-glycosylamine using 1-amino-N-acetylglucosamine as the nucleophile and L-aspartic acid beta-methyl ester as the beta-aspartyl donor. Kinetic studies indicated that beta-glycosylamine has 1390-fold higher reactivity than water in the de-beta-aspartylation of the beta-aspartylenzyme, indicative of the presence of a beta-glycosylamine binding sub-site at the substrate binding site of glycosylasparaginase. The reaction can be applied to glycosylaparaginase-catalyzed biosynthesis of novel glycoasparagines.

Aspartic Acid↗

DNA-hydrolyzing activity of Bence Jones proteins.

Of 18 monoclonal Bence Jones proteins purified from urine of patients with multiple myeloma, 4 were found to have a DNA-nicking activity. In contrast, all Bence Jones proteins tested showed detectable amidase activity against carbobenzoxy-L-valyl-glycyl-L-arginine p-nitroanilide. No correlation between the two activities was found. Four patients excreting Bence Jones protein with the DNA-nicking activity showed somewhat severe symptoms, suggesting that this activity may be related to the progressive deterioration of clinical status.

Adult↗

Nitrilase catalyzes amide hydrolysis as well as nitrile hydrolysis.

While amides were reported to be completely inert as substrates for all nitrilases reported to date, the nitrilase from Rhodococcus rhodochrous J1, which catalyzes the hydrolytic cleavage of the C-N triple bond in nitrile to form acid and ammonium, was surprisingly found to catalyze hydrolysis of amide to acid and ammonium stoichiometrically. This nitrilase exhibited a Km of 2.94 mM for benzamide, similar to that for benzonitrile as the original substrate (2.10 mM), but the Vmax for benzamide was six orders of magnitude lower than that for benzonitrile. Benzamide inhibited the nitrilase reaction in a reversible, apparently competitive manner. A mutant nitrilase containing alanine or serine instead of Cys165, which is essential for nitrilase catalytic activity, showed no amidase activity. This observation demonstrated that Cys165 plays a crucial role in the hydrolysis of amides as well as nitriles. Together with some reports that certain nitrilases were previously noted to produce low amounts of amide as a by-product from nitrile, the above unexpected findings suggested the existence of a common tetrahedral intermediate in the nitrilase reaction involving nitrile or amide as a substrate.

Aminohydrolases↗

Expression of a kallikrein-like protease from the snake venom: engineering of autocatalytic site in the fusion protein to facilitate protein refolding.

In order to circumvent the difficulty encountered in the expression and purification of the recombinant products in E. coli system, we have developed a novel and facile method of removing the polyhistidine tag from target proteins after heterologous gene expression. The expression of a serine protease (Tm-5) from Taiwan habu (Trimeresurus mucrosquamatus) is taken as an exemplar to illustrate the basic rationales and protocols involved. In place of an enterokinase recognition site, a polyhistidine tag linked to an autocatalyzed site based on cleavage specificity of the serine protease flanking on the 5'-end of Tm-5 clone sequence was engineered before protein expression in E. coli system. Renaturation of the fusion protein after expression revealed that the recombinant protease had refolded successfully from the inclusion bodies. Upon autocleavage of the expressed protease, the polyhistidine tag with additional amino acid residues appended to the N-terminus of the coding sequence is found to be removed accordingly. The protein expressed and purified by this new strategy possesses a molecular weight of approximately 28,000 in accord with the expected value for this venom protease. Further characterization of the recombinant protein employing a variety of techniques which include immunoblot analysis, RP-HPLC, ESI-MS, and N-terminal amino acid sequencing all shows indistinguishable properties to those of the isolated native protease. Most noteworthy is that the recombinant Tm-5 protease also exhibits amidase activity against N-benzoyl-Pro-Phe-Arg-p-nitroanilide, a unique and strict substrate for native Tm proteases reported previously.

Amidohydrolases↗

Fibrinogenolytic proteases isolated from the snake venom of Taiwan habu: serine proteases with kallikrein-like and angiotensin-degrading activities.

Two venom proteases with fibrinogenolytic activity were isolated from the venom of Taiwan habu (Trimeresurus mucrosquamatus), one major crotalid snake species in Taiwan. The purified enzymes showed a strong beta-fibrinogenolytic activity, cleaving the beta-chain of fibrinogen molecules specifically. They also showed strong kallikrein-like activity in vitro, releasing bradykinin from kininogen. The purified enzymes did not coagulate human plasma, yet decreasing fibrinogen levels in plasma and prolonging bleeding without formation of fibrin clots, indicating that both proteases have specificities different from thrombin and the thrombin-like proteases of snake venom reported previously. They also exhibit amidase activity against N-benzoyl-Pro-Phe-Arg-p-nitroanilide, which is a specific synthetic substrate for kallikrein-like proteases. Their stability at high temperatures was examined and found to be more stable when compared with ancrod and thrombin. Intravenous injection of either protease was shown to lower blood pressure in experimental rats. Most noteworthy is the observation that the proteases can cleave angiotensin I and release bradykinin from plasma kininogen in vitro, which is a strong vasodilator and probably responsible for the in vivo hypotensive effect of these venom proteases.

Amino Acid Sequence↗

Identification of target promoters for the Bacillus subtilis sigma X factor using a consensus-directed search.

The promoter selectivity of RNA polymerase (RNAP) can be altered by the association with alternative sigma subunits. Bacillus subtilis hosts a multitude of sigma factors, several of which coordinate the complex developmental program culminating in endospore formation. Genome sequencing has revealed an unanticipated seven new sigma factors of the highly divergent extracytoplasmic function (ECF) sub-family. Virtually nothing is known regarding either the promoter selectivity or the target genes for these newly identified sigma factors. We have used saturation mutagenesis to define a promoter consensus for recognition by one such ECF sigma factor, sigma X. The resulting consensus sequence was used to identify candidate sigma X target sites. Three newly identified sigma X-dependent promoters precede genes encoding regulatory proteins: an AbrB homolog (Abh), a putative response regulator aspartate phosphatase (RapD), and a regulator of autolysin expression (LytR). sigma X also contributes to the expression of CsbB, a putative membrane-bound glucosyl transferase that is partially controlled by the sigma B stress response sigma factor. Since LytR modulates the expression of the major autolytic amidase and CsbB may function in peptidoglycan synthesis or modification, we suggest that sigma X participates in the regulation of peptidoglycan synthesis and turnover.

Bacillus subtilis↗

Conservation of biotindase in mammals and identification of the putative biotinidase gene in Drosophila melanogaster.

Biotinidase deficiency is an autosomal recessively inherited disorder that is characterized by the failure to recycle biotin. Many of the known mutations that cause profound biotinidase deficiency are due to missense mutations that alter amino acids that are presumably important for proper enzyme function. Amino acids essential for biotinidase activity are likely conserved in species that are dependent on biotin recycling. To gain further insight into those amino acids or regions of biotinidase that are important for enzyme activity, we examined the conservation of the amino acids in various mammalian species. The amino acid sequences of biotinidase of monkey, cow, mouse, rat, and pig from the second putative transcription start site to the stop codon of the proteins are highly conserved when compared with each other and with human enzyme, but regions upstream of the second putative transcription start site are not conserved. In addition, because the entire genome of Drosophila is now available, we have identified the putative biotinidase gene in the insect and its corresponding amino acid sequence. The same 62-amino-acid region, which includes a cysteine and is an essential part of the active site of bacterial amidases and nitrilases, is highly conserved in all the mammalian and putative Drosophila biotinidases. Many of the missense mutations that cause biotinidase deficiency are located in these conserved regions of the mammalian and Drosophila biotinidases.

Amidohydrolases↗

Large-scale purification of human aspartylglucosaminidase: utilization of exceptional sodium dodecyl sulfate resistance.

Deficiency of human aspartylglucosaminidase (AGA, glycosylasparaginase, EC 3.5.1.26), a lysosomal amidase, results in the lysosomal storage disease aspartylglucosaminuria (AGU). This disorder is most prevalent in the genetically isolated Finnish population. To facilitate the detailed analysis of this important enzyme, which functions in the final degradation step of glycoproteins, we developed a novel purification method which makes possible a simple five-step 5000-fold purification to apparent homogeneity of human aspartylglucosaminidase from leukocytes. This purification procedure takes advantage of the remarkable SDS resistance of aspartylglucosaminidase as SDS-sensitive proteins aggregate preferentially at low (NH4)2SO4 concentrations in the presence of SDS. This new method should be applicable to the isolation of other SDS-resistant enzymes, e.g., superoxide dismutase. The homogeneous enzyme preparation exhibited a previously unreported fully denatured 19-kDa form of the alpha-subunit of aspartylglucosaminidase on SDS-polyacrylamide gel electrophoresis as a consequence of complete coating by SDS.

Ammonium Sulfate↗

Purification and characterization of a unique alkaline elastase from Micrococcus luteus.

Micrococcus luteus isolated from human skin secretes an alkaline protease which degrades elastin. M. luteus protease (MLP) was produced in the late logarithmic and stationary phases of growth. MLP, purified to homogeneity by a three-step process, had a molecular mass of 32,812 Da and an isoelectric point of 9.3. MLP was active and highly stable in solution for 24 h from pH 6.0 to 10.5; it had maximal activity at temperatures between 57 and 59 degrees C. The presence of calcium in the solution was essential for enzyme activity and to prevent autolysis. Optimal activity occurred between pH 9.0 and 9.5, with 60% maximal activity from pH 6.5 to 11.0. The enzyme was inhibited by the serine enzyme inhibitors phenylmethylsulfonyl fluoride and chymostatin but not by the metalloenzyme inhibitor 1,10-phenanthroline or sulfhydryl enzyme inhibitors. Casein, bovine serum albumin, ovalbumin, beta-lactoglobulin, and elastin were digested by the protease while collagen and keratin were resistant to digestion. MLP demonstrated both esterase and amidase activity on synthetic peptide substrates. MLP preferentially cleaved the Leu(15)-Tyr(16) and Phe(24)-Phe(25) bonds of the oxidized beta-chain of insulin. Longer digests of insulin and the pattern of activity against synthetic substrates suggest that MLP has a cleavage specificity for bulky, hydrophobic, or aromatic amino acids in the P(1) or P(1)' positions. Amino acid sequences from the N-terminus and internal peptides of MLP were unique.

Amino Acid Sequence↗

Analysis of 94 kb of the chlorella virus PBCV-1 330-kb genome: map positions 88 to 182.

Analysis of 94 kb of DNA, located between map positions 88 and 182 kb in the 330-kb chlorella virus PBCV-1 genome, revealed 195 open reading frames (ORFs) 65 codons or longer. One hundred and five of the 195 ORFs were considered major ORFs. Twenty-six of the 105 major ORFs resembled genes in the databases including three chitinases, a chitosanase, three serine/threonine protein kinases, two additional protein kinases, a tyrosine protein phosphatase, two ankyrins, an ornithine decarboxylase, a copper/zinc-superoxide dismutase, a proliferating cell nuclear antigen, a DNA polymerase, a fibronectin-binding protein, the yeast Ski2 protein, an adenine DNA methyltransferase and its corresponding DNA site-specific endonuclease, and an amidase. The genes for the 105 major ORFs were evenly distributed along the genome and, except for one noncoding 1788-nucleotide stretch, the genes were close together. Unexpectedly, a 900-bp region in the 1788-bp noncoding sequence resembled a CpG island.

Amino Acid Sequence↗