Analysis of simulated NMR order parameters for lipid bilayer structure determination.
(9/984)
The conventional formula for relating CD2 average order parameters to average methylenic travel is flawed when compared to molecular dynamics simulations of dipalmitoylphosphatidylcholine. Inspired by the simulated probability distribution functions, a new formula is derived that satisfactorily relates these quantities. This formula is used to obtain the average chain length , and the result agrees with the direct simulation result for . The simulation also yields a hydrocarbon thickness 2. The result = is consistent with a model of chain packing with both early chain termination and partial interdigitation of chains from opposing monolayers. The actual simulated area per lipid is easily obtained from the order parameters. However, when this method is applied to NMR order parameter data from dimyristoylphosphatidylcholine, the resulting is 10% larger than the currently accepted value. (+info)
Urease and hexadecylamine-urease films at the air-water interface: an x-ray reflection and grazing incidence x-ray diffraction study.
(10/984)
We report the results of surface x-ray scattering measurements performed on urease and hexadecylamine-urease films at the air-aqueous solution interface. It is demonstrated that although hexadecylamine does not form a stable monolayer on the pure aqueous surface, it does self-assemble into a stable, well-organized structure when spread on top of a urease film at the air-water interface. It is also likely that protein and hexadecylamine domains coexist at the interface. (+info)
Health aspects of the curing of synthetic rubbers.
(11/984)
A commonly used tread rubber formulation was cured in the laboratory under conditions simulating vulcanization in the Bag-O-Matic press. Volatile emissions were collected on charcoal and analyzed by combined GC-mass spectrometry. The compounds identified were either contaminants present in the raw material or reaction products. Some of these compounds were also identified in charcoal tube samples collected in the atmosphere of the industrial operations. Estimates based on the loss of weight of rubber during curing were used to predict airborne concentrations and compared to the concentrations actually found. The literature of the toxicity of raw materials and effluents was reviewed, and no acute or chronic toxicological effects would be anticipated. Information concerning potential carcinogenicity was not available and could not be evaluated. (+info)
Abnormal liver function tests following inadvertent inhalation of volatile hydrocarbons.
(12/984)
The use of aerosols containing volatile hydrocarbons in conditions of poor ventilation can result in accidental overexposure which can cause central nervous system effects and hepatic injury. We present a case in which inadvertent usage of an adhesive spray used to make greeting cards resulted in vague neurological symptoms and abnormal liver function tests both of which fully resolved on discontinuation. (+info)
Measurement of intracellular triglyceride stores by H spectroscopy: validation in vivo.
(13/984)
We validate the use of 1H magnetic resonance spectroscopy (MRS) to quantitatively differentiate between adipocyte and intracellular triglyceride (TG) stores by monitoring the TG methylene proton signals at 1.6 and 1.4 ppm, respectively. In two animal models of intracellular TG accumulation, intrahepatic and intramyocellular TG accumulation was confirmed histologically. Consistent with the histological changes, the methylene signal intensity at 1.4 ppm increased in both liver and muscle, whereas the signal at 1.6 ppm was unchanged. In response to induced fat accumulation, the TG concentration in liver derived from 1H MRS increased from 0 to 44.9 +/- 13.2 micromol/g, and this was matched by increases measured biochemically (2.1 +/- 1.1 to 46.1 +/- 10.9 micromol/g). Supportive evidence that the methylene signal at 1.6 ppm in muscle is derived from investing interfascial adipose tissue was the finding that, in four subjects with generalized lipodystrophy, a disease characterized by absence of interfacial fat, no signal was detected at 1.6 ppm; however, a strong signal was seen at 1.4 ppm. An identical methylene chemical shift at 1.4 ppm was obtained in human subjects with fatty liver where the fat is located exclusively within hepatocytes. In experimental animals, there was a close correlation between hepatic TG content measured in vivo by 1H MRS and chemically by liver biopsy [R = 0.934; P <.0001; slope 0.98, confidence interval (CI) 0.70-1.17; y-intercept 0.26, CI -0.28 to 0. 70]. When applied to human calf muscle, the coefficient of variation of the technique in measuring intramyocellular TG content was 11.8% in nonobese subjects and 7.9% in obese subjects and of extramyocellular (adipocyte) fat was 22.6 and 52.5%, respectively. This study demonstrates for the first time that noninvasive in vivo 1H MRS measurement of intracellular TG, including that within myocytes, is feasible at 1.5-T field strengths and is comparable in accuracy to biochemical measurement. In addition, in mixed tissue such as muscle, the method is clearly advantageous in differentiating between TG from contaminating adipose tissue compared with intramyocellular lipids. (+info)
Exposure to polycyclic aromatic hydrocarbons and genotoxic effects on nonsmoking Swedish road pavement workers.
(14/984)
OBJECTIVES: The objective of this study was to investigate exposure to polycyclic aromatic hydrocarbons (PAH) from asphalt fumes among Swedish road pavement workers and determine whether any effects could be detected with genotoxic tests. METHODS: The study included 28 nonsmoking road pavers and 30 nonsmoking referents. The concentration of PAH was determined in the breathing zone of the road pavers. 1-Hydroxypyrene was analyzed before and after shifts of asphalt work and during the afternoon for referents. Sister chromatid exchanges (SCE) and micronuclei (MN) were determined in peripheral lymphocytes. RESULTS: Several 3- or 4-ring PAH were found, and the analysis indicated that they occurred in bitumen fumes rather than in traffic fumes. The average total concentration of PAH was 2.3 (range 0.2-23.8) microg/m3. The concentration of 1-hydroxypyrene in urine was higher for the road pavers than for the referents, but there was no significant difference between the pre- and postshift values of the road pavers. The road pavers had no significant increase in SCE or MN. CONCLUSIONS: The study showed that Swedish road pavers have an increased exposure to PAH from bitumen fumes, but no genotoxic effects could be detected by SCE or MN tests. (+info)
The role of dermal irritation in the skin tumor promoting activity of petroleum middle distillates.
(15/984)
Petroleum middle distillates (PMDs), a class of hydrocarbons which boil between 350-700 degrees F, are tumor promoters in mouse skin. The promotional activity is produced under conditions that also result in local changes, including chronic irritation and epidermal hyperplasia. The present study was conducted by comparing equal weekly doses of irritating and minimally or nonirritating test materials, to assess whether tumor promotion was a secondary response to these effects. Four PMDs, C10-C14 normal paraffins (NP), lightly refined paraffinic oil (LRPO), Jet Fuel A (JF), and steam-cracked gas oil (SCGO), were evaluated. Test materials were applied undiluted (2x/week) or as 28.6% (7x/week) or 50% (4x/week) concentrations in mineral oil for 52 weeks following initiation with dimethylbenzanthracene (DMBA). When applied undiluted, all materials produced moderate irritation and significant increase in tumor incidence. When NP, LRPO, or JF were applied in mineral oil diluent, skin irritation was generally ameliorated and few, if any, tumors were produced. SCGO was irritating and produced a significant increase in tumor frequency when administered in mineral-oil diluent. These data indicate that the promotional activity of straight-run PMDs is likely related to chronic irritation at the application site and not to dose. Thus, when used appropriately in the absence of prolonged irritation, these materials should not present a tumorigenic hazard to humans. (+info)
A role for coenzyme M (2-mercaptoethanesulfonic acid) in a bacterial pathway of aliphatic epoxide carboxylation.
(16/984)
The bacterial metabolism of short-chain aliphatic alkenes occurs via oxidation to epoxyalkanes followed by carboxylation to beta-ketoacids. Epoxyalkane carboxylation requires four enzymes (components I-IV), NADPH, NAD(+), and a previously unidentified nucleophilic thiol. In the present work, coenzyme M (2-mercaptoethanesulfonic acid), a compound previously found only in the methanogenic Archaea where it serves as a methyl group carrier and activator, has been identified as the thiol and central cofactor of aliphatic epoxide carboxylation in the Gram-negative bacterium Xanthobacter strain Py2. Component I catalyzed the addition of coenzyme M to epoxypropane to form a beta-hydroxythioether, 2-(2-hydroxypropylthio)ethanesulfonate. Components III and IV catalyzed the NAD(+)-dependent stereoselective dehydrogenation of R- and S-enantiomers of 2-(2-hydroxypropylthio)ethanesulfonate to form 2-(2-ketopropylthio)ethanesulfonate. Component II catalyzed the NADPH-dependent cleavage and carboxylation of the beta-ketothioether to form acetoacetate and coenzyme M. These findings evince a newfound versatility for coenzyme M as a carrier and activator of alkyl groups longer in chain-length than methane, a function for coenzyme M in a catabolic pathway of hydrocarbon oxidation, and the presence of coenzyme M in the bacterial domain of the phylogenetic tree. These results serve to unify bacterial and Archaeal metabolism further and showcase diverse biological functions for an elegantly simple organic molecule. (+info)