New type dithiolene complex based on 4,5-(1,4-dioxane …
Alnumycin A (1, ) is an exceptional member of the aromatic polyketides in the sense that instead of typical deoxysugars, it contains an unusual 4′-hydroxy-5′-hydroxymethyl-2′,7′-dioxane moiety that mimics the structure of deoxysugars and is furthermore attached to the isochromanequinone aglycone via a C8-C1′ bond (, ). To date the biosynthetic pathway utilized for synthesis of the dioxane unit has been unknown, although we have previously cloned and successfully expressed the alnumycin gene cluster heterologously in Streptomyces albus (A and B) to enable efficient manipulation of the pathway (). Initial knockout studies also identified the involvement of two genes, alnA and alnB, in the biosynthesis and transfer of the dioxane moiety as both single-gene mutants produced prealnumycin (2, ) as their main metabolite ().
EPA External Review Draft of 1,4 Dioxane ..
Reactions were set up in 10 mM Trizma-HCl (pH 6.8) (pH 6 for Aln6), 25 mM NaCl, 25 mM KCl, ≥10% glycerol, and substrates in 2–5% DMSO. For all enzymes except Aln6, the oxygen concentration was reduced using the glucose oxidase (100 nM)-catalase (1.5 μM) system in 60 mM -glucose. Incubation for 1–3.5 h at 288 K (296 K for Aln6) was followed by extraction with 3 × 0.5–1 volume of CHCl3. The CHCl3 extracts were air-dried and dissolved in acetonitrile for HPLC analysis, which was conducted using either the LiChroCART 250-4 column eluted with 20 mM aqueous ammonium acetate and a 55–100% acetonitrile gradient (), or the SunFire C18 column eluted with 0.1% aqueous formic acid and a 15–100% acetonitrile gradient (). Oxygen consumption by Aln6 was monitored at 296 K with an MI-730 oxygen electrode (Microelectrodes, Inc.). For end-point assays with Aln6, individual 100 µL reactions were quenched by chloroform extraction followed by quantitative HPLC analysis of each organic phase, and a peroxidase assay of each water phase to estimate the hydrogen peroxide concentration. The latter was monitored spectrophotometrically at 734 nm using 0.23 mg/mL peroxidase, 0.5 mM 2,2′-azinobis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) and known concentrations of hydrogen peroxide as a standard. Formation of a stoichiometric amount of H2O2 and 4 could not be observed because of increased instability of H2O2 caused by Aln6. The preparative scale enzymatic production of 7 is described in . The high resolution mass spectra for both 7 and the enzymatically synthesized 1 and 4–6 were obtained by HPLC-ESI-MS as described above.
Figure 4. 1,4-Dioxane degradation and expression of relevant genes in CB1190 exposed to individual chlorinated solvents. (A) Kinetics of 1000 μg L–1 1,4-dioxane biodegradation in the presence of 5 mg L–1 individual solvent (1,1-DCE, cis-1,2-DCE, TCE, and TCA). This figure was extracted from for comparison with the gene regulation figure. (B) Fold change in transcript copy numbers of dioxane monooxygeanse () and aldehyde monooxygenase () at 0, 2, 6, and 12 h. CB1190 culture with 1000 μg L–1 1,4-dioxane was exposed to 5 mg L–1 of solvents (1,1-DCE, cis-1,2-DCE, TCE, or TCA). The circles represent 1,4-dioxane concentrations.
7 All reactions was carried out in 1,4-dioxane at 25 ..
The cytochrome P450 superfamily is one of the most studied drug-metabolizing enzyme superfamilies, having a great deal of individual variability in response to chemicals. Cytochrome P450 is a convenient generic term used to describe a large superfamily of enzymes pivotal in the metabolism of innumerable endogenous and exogenous substrates. The term cytochrome P450 was first coined in 1962 to describe an unknown pigment in cells which, when reduced and bound with carbon monoxide, produced a characteristic absorption peak at 450 nm. Since the early 1980s, cDNA cloning technology has resulted in remarkable insights into the multiplicity of cytochrome P450 enzymes. To date, more than 400 distinct cytochrome P450 genes have been identified in animals, plants, bacteria and yeast. It has been estimated that any one mammalian species, such as humans, may possess 60 or more distinct P450 genes (Nebert and Nelson 1991). The multiplicity of P450 genes has necessitated the development of a standardized nomenclature system (Nebert et al. 1987; Nelson et al. 1993).
(iii); formaldehyde, K 2 CO 3, 1,4-dioxane, 3 h ..
Consumption of alcohol (ethanol) can influence susceptibility to many toxic chemicals in several ways. It can influence the absorption rate and distribution of certain chemicals in the bodyfor example, increase the gastrointestinal absorption rate of lead, or decrease the pulmonary absorption rate of mercury vapour by inhibiting oxidation which is necessary for retention of inhaled mercury vapour. Ethanol can also influence susceptibility to various chemicals through short-term changes in tissue pH and increase in the redox potential resulting from ethanol metabolism, as both ethanol oxidizing to acetaldehyde and acetaldehyde oxidizing to acetate produce an equivalent of reduced nicotinamide adenine dinucleotide (NADH) and hydrogen (H+ ). Because the affinity of both essential and toxic metals and metalloids for binding to various compounds and tissues is influenced by pH and changes in the redox potential (Teliman 1995), even a moderate intake of ethanol may result in a series of consequences such as: (1) redistribution of long-term accumulated lead in the human organism in favour of a biologically active lead fraction, (2) replacement of essential zinc by lead in zinc-containing enzyme(s), thus affecting enzyme activity, or influence of mobilized lead on the distribution of other essential metals and metalloids in the organism such as calcium, iron, copper and selenium, (3) increased urinary excretion of zinc and so on. The effect of possible aforementioned events can be augmented due to the fact that alcoholic beverages can contain an appreciable amount of lead from vessels or processing (Prpic-Majic et al. 1984; Teliman et al. 1984; 1993).
Organic Chemistry Ethers | Ether | Chemical Reactions
The critical effects can be of two types: those considered to have a threshold and those for which there may be some risk at any exposure level (non-threshold, genotoxic carcinogens and germ mutagens). Whenever possible, appropriate human data should be used as a basis for the risk assessment. In order to determine the threshold effects for the general population, assumptions concerning the exposure level (tolerable intake, biomarkers of exposure) have to be made such that the frequency of the critical effect in the population exposed to a given hazardous agent corresponds to the frequency of that effect in the general population. In lead exposure, the maximum recommended blood lead concentration for the general population (200 µg/l, median below 100 µg/l) (WHO 1987) is practically below the threshold value for the assumed critical effect-the elevated free erythrocyte protoporphyrin level, although it is not below the level associated with effects on the CNS in children or blood pressure in adults. In general, if data from well-conducted human population studies defining a no observed adverse effect level are the basis for safety evaluation, then the uncertainty factor of ten has been considered appropriate. In the case of occupational exposure the critical effects may refer to a certain part of the population (e.g. 10%). Accordingly, in occupational lead exposure the recommended health-based concentration of blood lead has been adopted to be 400 mg/l in men where a 10% response level for ALA-U of 5 mg/l occurred at PbB concentrations of about 300 to 400 mg/l. For the occupational exposure to cadmium (assuming the increased urinary excretion of low-weight proteins to be the critical effect), the level of 200 ppm cadmium in renal cortex has been regarded as the admissible value, for this effect has been observed in 10% of the exposed population. Both these values are under consideration for lowering, in many countries, at the present time (i.e.,1996).