End Product Of Reaction Research Articles

Escherichia coli biotin protein ligase: characterization and development of a high-throughput assay

The rapid rise in pathogenic bacteria resistant to current treatments, coupled with the paucity of new therapeutic agents in the pipeline, has resulted in a significant need for new antibiotics. One strategy to overcome resistance requires new chemical entities that inhibit key enzymes in essential metabolic processes that have not been previously targeted and for which there is no preexisting drug resistance. Biotin protein ligase (BPL), required to complete acetyl CoA carboxylase’s capability for fatty acid biosynthesis, is one target that has not yet been fully explored. However, its application in large-scale compound screens has been limited due to the lack of a truly high-throughput assay for enzyme activity. Here we report a novel assay system for BPL from Escherichia coli (BirA). This assay employs fluorescence polarization technology together with a unique peptide substrate for BirA. Additionally, the multiple handling steps and requirement for radiolabeled ligands associated with previous assays have been eliminated. Kinetic analysis of MgATP (Km 0.25±0.01mM) and biotin (Km 1.45±0.15μM) binding produced results consistent with published data. Inhibition studies with end products of the BPL reaction, AMP and pyrophosphate, further validated the assay. Statistical analysis, performed upon both intraassay and interassay results (n = 30), showed the coefficient of variance to be <10% across all data sets. Furthermore, Z′ factors between 0.5 and 0.8 demonstrated the utility of this technology in high-throughput applications.

The influence of photocatalytic interior paints on indoor air quality

A clean indoor air is important for the well-being and health of people. Lately, new photocatalytic paints have been launched on the market, which are claimed to have air-purifying effects. Photocatalysis initiates radical reactions. Radicals are formed when a photocatalyst (e.g. TiO2) is subjected to radiation. Typical radicals are the hydroxyl radical (OH) and the superoxide radical (O2−). Radicals cause chain reactions, which degrade and decompose organic compounds. The end products of these chain reactions are water and carbon dioxide, if the reactions are fully completed (mineralization). If mineralization does not take place, then a great number of side products can be formed, whose properties are not well understood. The side products of photocatalytic reactions can be permanent and stabile. The decomposition of indoor air impurities on the surface of photocatalytic paints is not obvious. The ability of photocatalytic indoor paints to reduce chemical indoor air impurities is the key issue of this study. Six different paints with different binder systems, such as lime, polyorganic siloxane, silica sol–gel and organic binders, were examined. The experiments were divided into three topics: degradation of an organic binder, photocatalytic decomposition of formaldehyde, and a volatile organic compound (VOC) mixture consisting of five different indoor air VOCs. All tests were carried out in an environmental test chamber under dynamic conditions. The test results indicate that many indoor pollutants are generated under normal- and UVA-light. Typical compounds formed include formaldehyde, acetone, acetaldehyde, etc. A clear decrease of formaldehyde or the VOC mixture concentration was not observed. All possibly generated compounds could not be collected or analyzed in this research project, but the measurements show that photocatalytic reactions do not generate only carbon dioxide and water. Photocatalytic decomposition of indoor air impurities can, however, produce many side products, which may be stabile and harmful.

Kinetics of Activated Carbon Promoted Ozonation of Polyphenol Mixtures in Water

The kinetics of the activated carbon ozonation of mixtures of three polyphenol compounds (gallic acid, tyrosol, and syringic acid) in water has been studied from the application of a double mechanism of reactions to experimental data. These mechanisms involve direct ozone reactions with starting polyphenols and hydroxyl free radical reactions with intermediates and end reaction products, mainly saturated carboxylic acids (the concentration being represented with the chemical oxygen demand, COD). The direct ozone reaction mechanism develops during the initial period (15−60 min) where polyphenols are removed. The kinetic regime of the process was fast of pseudo first order, and at 25 °C and pH 5 the direct rate constants of the reactions between ozone and gallic acid, syringic acid, and tyrosol were determined from different kinetic methods. Once polyphenols disappear and saturated carboxylic acids (end reaction products) are present, the removal of these compounds goes through hydroxyl free radical oxidation. This second mechanism involves the reaction of ozone and the organic matter, through hydrogen peroxide formation, both in bulk water and on the carbon surface, as the initiating step of hydroxyl radical formation. In the absence of activated carbon, the activation energy of the bulk water ozone−organic matter reaction was found to be 36.3 ± 4.5 kcal·mol-1. In the presence of activated carbon, at the conditions here applied in addition to bulk water chemical reaction, the process depends on mass-transfer resistances, and the values of the volumetric liquid-side and individual liquid−solid external mass-transfer coefficients were found to be 0.71 ± 0.05 min-1 and 1.19 ± 0.10 × 10-3 m·min-1, respectively.

Formation of adducts in the reaction of glyoxal with 2′-deoxyguanosine and with calf thymus DNA

The reactions of glyoxal with 2′-deoxyguanosine and calf thymus single- and double-stranded DNA in aqueous buffered solutions at physiological conditions resulted in the formation of two previously undetected adducts in addition to the known reaction product 3-(2′-deoxy-β- d- erythro-pentofuranosyl)-5,6,7-trihydro-6,7-dihydroxyimidazo[1,2- a]purine-9-one (Gx-dG). The adducts were isolated and purified by reversed-phase liquid chromatography and structurally characterised by UV absorbance, mass spectrometry, 1H and 13C NMR spectroscopy. The hitherto unknown adducts were identified as: 5-carboxymethyl-3-(2′-deoxy-β- d- erythro-pentofuranosyl)-5,6,7-trihydro-6,7-dihydroxyimidazo[1,2- a]purine-9-one (Gx 2-dG) and N 2-(carboxymethyl)-9-(2′-deoxy-β- d- erythro-pentofuranosyl)-purin-6(9 H)-one (Gx 1-dG). Both adducts were shown to arise from Gx-dG. Gx-dG and Gx 2-dG were found to be unstable and partly transformed to Gx 1-dG, which is a stable adduct and seems to be the end-product of the glyoxal reaction with 2′-deoxyguanosine. All adducts formed in the reaction of glyoxal with 2′-deoxyguanosine were observed in calf thymus DNA. Also in DNA, Gx 1-dG was the only stable adduct. The transformation of Gx-dG to Gx 1-dG seemed to take place in single-stranded DNA and therefore, Gx 1-dG may be a potentially reliable biomarker for glyoxal exposure and may be involved in the genotoxic properties of the compound.

Kinetical Study of the Photoinduced Degradation of Imidacloprid in Aquatic Media

AbstractThe photoinduced degradation of the insecticide imidacloprid in natural water samples was performed in order to describe its abiotic degradation. Numerous degradation products could be identified with the help of spectroscopic methods. The main photoproducts were 1‐[(6‐chloro‐3‐pyridinyl)methyl]‐N‐nitroso‐2‐imidazolidinimine, 1‐[(6‐chloro‐3‐pyridinyl)methyl]‐2‐imidazolidinimine (which is known to be more toxic for warm‐blooded animals than imidacloprid) and 1‐[(6‐chloro‐3‐pyridinyl)methyl]‐2‐imidazolidinone. Besides numerous other degradation products, 6‐chloro‐nicotine‐amide was identified as the end product of the photolytic reaction. The photoinduced reaction of imidacloprid followed pseudo first‐order reaction kinetics and resulted from a triplet‐controlled intermediate state with a triplet energy between 281–290 kJ/mol and an half‐life time of 4.6×10–9 s. With the help of measured quantum yields (ΦS), the half‐life time of imidacloprid in natural waters was estimated at 3 days. The calculated half‐life times of 1‐[(6‐chloro‐3‐pyridinyl)methyl]‐2‐imidazolidinimine was much shorter, 0.24 days, while those of 1‐[(6‐chloro‐3‐pyridinyl)methyl]‐2‐imidazolidinone and 6‐chloro‐nicotine‐amide were higher at 270 and 660 days, respectively.

DNA sequence- and conformation-directed positioning of nucleosomes by chromatin-remodeling complexes

Chromatin-remodeling complexes can translocate nucleosomes along the DNA in an ATP-coupled reaction. This process is an important regulator of all DNA-dependent processes because it determines whether certain DNA sequences are found in regions between nucleosomes with increased accessibility for other factors or wrapped around the histone octamer complex. In a comparison of seven different chromatin-remodeling machines (ACF, ISWI, Snf2H, Chd1, Mi-2, Brg1, and NURF), it is demonstrated that these complexes can read out DNA sequence features to establish specific nucleosome-positioning patterns. For one of the remodelers, ACF, we identified a 40-bp DNA sequence element that directs nucleosome positioning. Furthermore, we show that nucleosome positioning by the remodelers ACF and Chd1 is determined by a reduced affinity to the end product of the translocation reaction. The results suggest that the linkage of differential remodeling activities with the intrinsic binding preferences of nucleosomes can result in establishing distinct chromatin structures that depend on the DNA sequence and define the DNA accessibility for other protein factors.

Carbon Monoxide Can Prevent Acute Lung Injury Observed After Ischemia Reperfusion of the Lower Extremities

Pulmonary expression of heme oxygenase has been observed in multiple studies. This expression has been found beneficial in decreasing the severity of acute lung injury (ALI) post ischemia-reperfusion (I/R). The aim of this study was to assess the role of exogenous administration of the end-products of heme oxygenase reaction, carbon monoxide, and bilirubin, in the severity of ALI. We compared five groups of rats (n = 7/group) including a sham group and four I/R of the lower extremities by clamping the abdominal aorta for 2 h followed by reperfusion for 2 h. The four I/R groups included a control group, one pretreated with bilirubin (50 micromol/kg IV), another with inhaled carbon monoxide (CO) (250 ppm), and the last pretreated with both. The severity of ALI has been evaluated by a histological assay grading neutrophilic infiltration, as well as a study of the microvascular permeability using the Evans blue. The administration of CO prevented pulmonary microvascular permeability alteration noted after I/R of the lower limbs (pulmonary content of Evans blue: 141 +/- 23 microg/g of tissue in the isolated I/R group versus 68 +/- 34 microg/g of tissue in CO group; P < 0.001). Histologically CO administration inhibited neutrophilic sequestration observed after I/R. On the other hand, treatment by bilirubin alone (50 micromol/kg IV) did not modify the extent of pulmonary injury. Exogenous administration of carbon monoxide by inhalation at low doses prevented ALI post-I/R in this model.

A covered particle deactivation model and an expanded Dunford mechanism for the kinetic analysis of the immobilized SBP/phenol/hydrogen peroxide system

Abstract An expanded version of the Dunford mechanism, which extends the initial peroxidase cycle to the reaction products, was developed and applied to the kinetic analysis of the immobilized soybean peroxidase/phenol/hydrogen peroxide system. At the same time, an enzyme deactivation model, based on the gradual covering of the catalytic particles by the products originated during the reaction (radicals and end-products, oligomers/polymers), was proposed. From the reaction mechanism and deactivation model, the kinetic equations for phenol, dimeric compounds and hydrogen peroxide were obtained and applied to the design of a batch reactor. In order to check the mechanism, an immobilized derivative of the enzyme on PG-glutaraldehyde, which retains 74% of the free enzyme activity and which was characterized in a previous work, was used. In a batch reactor, and without adding protective agents, several series of experiments were carried out, and the influence of operational variables on the conversion was studied. Phenol removal percentages of more than 90% were obtained in some of the tested situations. Using a method for initial rate estimation, three of the model parameters were calculated. In order to determine the remaining parameters, half of the experimental data series and a program for error minimization, based on the Simplex algorithm of Nelder and Mead, were used. A good fitting between the data and the model was obtained, and the typical deviation was 3.27%. Using the data from the remaining series, which had not been used for determining the parameters, the model was checked and even better agreement, with 2.72% typical deviation, was obtained, which confirms the validity of the proposed model.

H2S, Endoplasmic Reticulum Stress, and Apoptosis of Insulin-secreting Beta Cells

Cystathionine gamma-lyase (CSE) is a key enzyme in the trans-sulfuration pathway, which uses L-cysteine to produce hydrogen sulfide (H2S). Functional changes of pancreatic beta cells induced by endogenous H2S have been reported, but the effect of the CSE/H2S system on pancreatic beta cell survival has not been known. In this study, we demonstrate that H2Sat physiologically relevant concentrations induced apoptosis of INS-1E cells, an insulin-secreting beta cell line. Transfection of INS-1E cells with a recombinant defective adenovirus containing the CSE gene (Ad-CSE) resulted in a significant increase in CSE expression and H2S production. Ad-CSE transfection also stimulated apoptosis. The other two end products of CSE-catalyzed enzymatic reaction, ammonium and pyruvate, had no effects on INS-1E cell apoptosis, indicating that overexpression of CSE may stimulate INS-1E cell apoptosis via increased endogenous production of H2S. Both exogenous H2S (100 microM) and Ad-CSE transfection inhibited ERK1/2 but activated p38 MAPK. Interestingly, BiP and CHOP, two indicators of endoplasmic reticulum (ER) stress, were up-regulated in H2S-and CSE-mediated apoptosis in INS-1E cells. After suppressing CHOP mRNA expression, H2S-induced apoptosis of INS-1E cells was significantly decreased. Inhibition of p38 MAPK, but not of ERK1/2, inhibited the expression of BiP and CHOP and decreased H2S-stimulated apoptosis, suggesting that p38 MAPK activation functions upstream of ER stress to initiate H2S-induced apoptosis. It is concluded that H2S induces apoptosis of insulin-secreting beta cells by enhancing ER stress via p38 MAPK activation. Our findings may help unmask a novel role of CSE/H2S system in regulating pancreatic functions under physiological condition and in diabetes.

Transmission electron microscopy investigation of substitution reactions from carbon nanotube template to silicon carbide nanowires

Substitution reactions between multiwalled carbon nanotubes and silicon monoxide vapour have been investigated using transmission electron microscopy. Different reactions occurred inside the multiwalled nanotubes and on the nanotube external surfaces, resulting in the formation of silicon carbide nanowires with a core–shell structure. The substitution reaction process and end products are strongly affected by nanotube structures and a ball milling treatment of the starting materials.

Elucidation of the mechanism and end products of glutaraldehyde crosslinking reaction by X‐ray structure analysis

Glutaraldehyde has been used for several decades as an effective crosslinking agent for many applications including sample fixation for microscopy, enzyme and cell immobilization, and stabilization of protein crystals. Despite of its common use as a crosslinking agent, the mechanism and chemistry involved in glutaraldehyde crosslinking reaction is not yet fully understood. Here we describe feasibility study and results obtained from a new approach to investigate the process of protein crystals stabilization by glutaraldehyde crosslinking. It involves exposure of a model protein crystal (Lysozyme) to glutaraldehyde in alkaline or acidic pH for different incubation periods and reaction arrest by medium exchange with crystallization medium to remove unbound glutaraldehyde. The crystals were subsequently incubated in diluted buffer affecting dissolution of un-crosslinked crystals. Samples from the resulting solution were subjected to protein composition analysis by gel electrophoresis and mass spectroscopy while crosslinked, dissolution resistant crystals were subjected to high resolution X-ray structural analysis. Data from gel electrophoresis indicated that the crosslinking process starts at specific preferable crosslinking site by lysozyme dimer formation, for both acidic and alkaline pH values. These dimer formations were followed by trimer and tetramer formations leading eventually to dissolution resistant crystals. The crosslinking initiation site and the end products obtained from glutaraldehyde crosslinking in both pH ranges resulted from reactions between lysine residues of neighboring protein molecules and the polymeric form of glutaraldehyde. Reaction rate was much faster at alkaline pH. Different reaction end products, indicating different reaction mechanisms, were identified for crosslinking taking place under alkaline or acidic conditions.

Protein Kinase Cδ Plays a Non-redundant Role in Insulin Secretion in Pancreatic β Cells

Protein kinase C (PKC) is considered to modulate glucose-stimulated insulin secretion. Pancreatic beta cells express multiple isoforms of PKCs; however, the role of each isoform in glucose-stimulated insulin secretion remains controversial. In this study we investigated the role of PKCdelta, a major isoform expressed in pancreatic beta cells on beta cell function. Here, we showed that PKCdelta null mice manifested glucose intolerance with impaired insulin secretion. Insulin tolerance test showed no decrease in insulin sensitivity in PKCdelta null mice. Studies using islets isolated from these mice demonstrated decreased glucose- and KCl-stimulated insulin secretion. Perifusion studies indicated that mainly the second phase of insulin secretion was decreased. On the other hand, glucose-induced influx of Ca2+ into beta cells was not altered. Immunohistochemistry using total internal reflection fluorescence microscopy and electron microscopic analysis showed an increased number of insulin granules close to the plasma membrane in beta cells of PKCdelta null mice. Although PKC is thought to phosphorylate Munc18-1 and facilitate soluble N-ethylmaleimide-sensitive fusion protein attachment protein receptors complex formation, the phosphorylation of Munc18-1 by glucose stimulation was decreased in islets of PKCdelta null mice. We conclude that PKCdelta plays a non-redundant role in glucose-stimulated insulin secretion. The impaired insulin secretion in PKCdelta null mice is associated with reduced phosphorylation of Munc18-1.

Production of Anti‐Digoxigenin Antibody HRP Conjugate for PCR‐ELISA DIG Detection System

There are several methods used to visualize the end product of polymerase chain reactions. One of these methods is an ELISA‐based detection system (PCR‐ELISA) which is very sensitive and can be used to measure the PCR products quantitatively by a colorimetric method. According to this technique, copies of DNA segments from genomic DNA are amplified by PCR with incorporation of digoxigenin‐11‐dUTP. Samples are analyzed in a microtiter plate format by alkaline denaturation and are hybridized to biotinylated allele‐specific capture probes bound to streptavidin coated plates. Use of the produced anti‐digoxigenin antibody horseradish peroxidase conjugate and the substrate 2,2′‐azino‐di‐3‐ethylbenzthiazolinsulfonate (ABTS) detected the hybridized DNA. One of the key components in this procedure is the anti‐digoxigenin antibody HRP conjugate. Described here is the preparation, purification, and characterization of anti‐digoxigenin antibody HRP conjugate for use in the PCR‐ELISA DIG detection system. Several biochemical protocols and modifications were applied to increase the sensitivity and specificity of this conjugate for an efficient and cost‐effective product.

Prenyltransferase of larval and adult M. sexta corpora allata

Prenyltransferase activity derived from the corpora allata (CA) of the lepidopteran insect, Manduca sexta, has been characterized. The coupling of allylic substrates DMAPP and GPP with the non-allylic substrate IPP was evaluated using CA homogenates of both the larval and adult stages of development. The effect of additives and inhibitors, assay conditions, and metal preference were examined. The cellular location of prenyltransferase activity was also investigated. We found subtle differences between larval and adult preparations, including metal and detergent preference, and while larval prenyltransferase activity was strictly cytosolic, prenyltransferase derived from adult CA was found in both the cytosolic and pellet fractions. Differences in kinetics as a function of development were also noted. When GPP was utilized as allylic substrate, adult prenyltransferase displayed cooperative behavior; while with DMAPP, biphasic kinetics were observed. In fifth instar larvae, prenyltransferase activity was highest on days 1–2 and reaction end products changed as a result of insect age. Taken together, these results suggest that larval and adult prenyltransferase of M. sexta have distinct enzymological properties and that the adult CA possess more than one prenyltransferase.

Mouse Transthyretin-related Protein Is a Hydrolase which Degrades 5-Hydroxyisourate, the End Product of the Uricase Reaction

Mouse Transthyretin-related Protein Is a Hydrolase which Degrades 5-Hydroxyisourate, the End Product of the Uricase Reaction

Enzyme Fragment Complementation Binding Assay for p38α Mitogen-Activated Protein Kinase to Study the Binding Kinetics of Enzyme Inhibitors

The majority of protein kinase assays used in drug discovery research are enzyme activity assays. These assays are based on the measurement of phosphorylated protein or peptide substrate, which is the end product of the enzyme reaction. Since most kinase inhibitors are ATP competitive, prediction of the activity of compounds in cellular systems based on potency values in enzyme activity assays is complex, as this should take into account the affinity of the enzyme for ATP and the cellular ATP concentration. The fact that some of the most successful kinase inhibitors, such as STI 571 (imatinib mesylate, Gleevec, Novartis Pharmaceuticals, East Hanover, NJ), act through binding to the inactive isoform of the kinase provides another limitation of enzyme activity assays. Binding assays allow separate measurement of compound affinity to active and inactive kinase and do not require ATP or substrate in the reaction. Recently, a non-radioactive kinase binding assay for p38 mitogen-activated protein kinase has become available from DiscoveRx (Fremont, CA). The assay method, called HitHunter, utilizes enzyme fragment complementation of Escherichia coli beta-galactosidase to generate an assay signal by chemiluminescence. We have reconfigured the commercial assay kit to study the binding kinetics of two known reference inhibitors of the alpha-isoform of p38, the pyridinyl imidazole SB 203580 and the diaryl urea BIRB 796. Our data confirm the slow association kinetics of BIRB 796 as compared to SB 203580, which corresponded with the requirement of a relatively long preincubation time to obtain maximal effect in a cellular assay. Although neither of the two compounds showed preference for either active or inactive p38alpha, our data demonstrate that the HitHunter kinase binding assay can be used to select compounds that specifically target inactive kinase.

Reductive dechlorination of 1,2,4-trichlorobenzene with palladized nanoscale Fe 0 particles supported on chitosan and silica

In this study, nanoscale Pd–Fe particles, with diameters less than 100 nm, were synthesized and dispersed over the chitosan and silica supports. Three different Pd–Fe particles were synthesized, namely 0.1% Pd–Fe, 0.5% Pd–Fe and 1.0% Pd–Fe. SEM images confirmed that the Pd–Fe particles were dispersed over the surface of the supports while SEM-EDX confirmed evenly distribution of Pd over Fe 0. α-Fe 0 crystallites were identified by means of XRD and observed in TEM. Reductive dechlorinations of 1,2,4-trichlorobenzene (1,2,4-TCB) with the nanoscale Pd–Fe/chitosan and Pd–Fe/silica were carried out in the batch experiment system. Disappearance of the parent species and formation of the reaction intermediates and end product were monitored at discrete times. The results show that the nano-scale Pd–Fe particles were able to completely dechlorinate the chlorinated benzenes within a very short timescale. Complete dechlorinations of 1,2,4-TCB to benzene were achieved within 60 min with the 1.0% Pd–Fe/chitosan and within 100 min with the 1.0% Pd–Fe/silica. Reaction rates were observed to increase with increasing Pd content of the Pd–Fe/support. The reactions apparently followed pseudo-first-order kinetics with respect to the 1,2,4-TCB transformation. A kinetic model is constructed to fit the experimental results for the reactions, enabling identification of the major and minor dechlorination pathways of 1,2,4-TCB. The model suggests that the 1,2,4-TCB transformation mainly followed the primary pathway of direct reductive dechlorination to benzene and secondary pathway of sequential hydrogenolysis to 1,2-dichlorobenzene (1,2-DCB) and then chlorobenzene (CB) or benzene.

Thermally Induced Polytype Transformations among the Layered Double Hydroxides (LDHs) of Mg and Zn with Al

The hydrotalcite-like layered double hydroxide (LDH) of Mg with Al shows dramatic changes in the peaks arising from the (h0l)/(0kl) family of reflections in its powder X-ray diffraction pattern during thermal treatment. DIFFaX simulations show that these changes arise due to the transformation of the disordered 3R1 polytype into the 1H polytype on dehydration. The 1H polytype is an essential precursor to the decomposition reaction, which results in the formation of an oxide residue with the rock salt structure. In contrast, the LDH of Zn with Al does not undergo any such transformation, retaining the structure of the 3R1 polytype until decomposition into the oxide residue. Given the poor octahedral site preference of the Zn2+ ion, the 1H polytype is neither structurally stable nor is it topochemically necessary for the thermal decomposition of the Zn-Al LDH, the end product of the decomposition reaction being an oxide with the wurtzite structure.

Photochemical formation of perchlorate from aqueous oxychlorine anions

Evidence of atmospherically produced perchlorate is being accumulated, yet information regarding its formation process is largely unknown. For the first time, the present study demonstrates that perchlorate can be generated as an end-product of photochemical transformation reactions of chlorine precursors such as aqueous salt solutions of hypochlorite, chlorite, and chlorate upon exposure to ultraviolet (UV) radiation. For example, under exposure to UV light from photochemical reactor lamps at a peak wavelength of 253.7 nm for 7 days, the observed perchlorate concentrations were 5, 25, and 626 μg/L at initial chlorite concentrations of 100, 1000, and 10,000 mg/L, respectively. In addition, perchlorate was generated within 7 days from aqueous chlorite solutions at mid-latitude (33°59′N, 101°89′W) spring and summer solar radiation. Via UV radiation from the artificial lamps and sunlight, chlorite was converted to chloride (68%) and chlorate (32%) as end-products on the basis of molar percentage. However, perchlorate was not detected from aqueous chloride solutions at initial concentrations up to 10,000 mg/L under the experimental conditions. Relevant mechanistic pathways were proposed based on the fact that chlorine dioxide (as a primary intermediate) may play a significant role in phototransformation of the precursors leading to perchlorate.

Cysteine S-conjugate β-lyases

Cysteine S-conjugate beta-lyases are pyridoxal 5'-phosphate-containing enzymes that catalyze beta-elimination reactions with cysteine S-conjugates that possess an electron-withdrawing group attached at the sulfur. The end products of the beta-lyase reaction are pyruvate, ammonium and a sulfur-containing fragment. If the sulfur-containing fragment is reactive, the parent cysteine S-conjugate may be toxic, particularly to kidney mitochondria. Halogenated alkenes are examples of electrophiles that are bioactivated (toxified) by conversion to cysteine S-conjugates. These conjugates are converted by cysteine S-conjugate beta-lyases to thioacylating fragments. Several cysteine S-conjugates found in allium foods (garlic and onion) are beta-lyase substrates. This finding may account in part for the chemopreventive activity of allium products. This review (1) identifies enzymes that catalyze cysteine S-conjugate beta-lyase reactions, (2) suggests that toxicant channeling may contribute to halogenated cysteine S-conjugate-induced toxicity to mitochondria, and (3) proposes mechanisms that may contribute to the antiproliferative effects of sulfur-containing fragments eliminated from allium-derived cysteine S-conjugates.