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PubMed2005

Synthesis and evaluation of 1-deoxy-D-xylulose 5-phosphoric acid analogues as alternate substrates for methylerythritol phosphate synthase.

[structure: see text] Four deoxyxylulose phosphate (DXP) analogues were synthesized and evaluated as substrates/inhibitors for methylerythritol phosphate (MEP) synthase. In analogues CF(3)-DXP (1), CF(2)-DXP (2), and CF-DXP (3), the three methyl hydrogens at C1 of DXP were sequentially replaced by fluorine. In the fourth analogue, Et-DXP (4), the methyl group in DXP was replaced by an ethyl moiety. Analogues 1, 2, and 4 were not substrates for MEP synthase under normal catalytic conditions and were instead modest inhibitors with IC(50) values of 2.0, 3.4, and 6.2 mM, respectively. In contrast, 3 was a good substrate (k(cat) = 38 s(-)(1), K(m) = 227 muM) with a turnover rate similar to that of the natural substrate. These results are consistent with a retro-aldol/aldol mechanism rather than an alpha-ketol rearrangement for the enzyme-catalyzed conversion of DXP to MEP.

Aldose-Ketose Isomerases↗
PubMed2005

Propane fuel cells using phosphoric-acid-doped polybenzimidazole membranes.

Propane fuel cells using H(3)PO(4)-doped polybenzimidazole polymer membranes produce low and unsustainable current densities at temperatures up to 250 degrees C under anhydrous conditions. Stable intermediate species blocked the surface of noble metal anode catalysts, and the intermediate species could not react further into desorbable final products. In contrast, when water was introduced by light humidification (S(r) 0.08%) of the propane stream, sustainable and higher current densities were achieved. Water participated in the reaction sequence to form surface-bound hydrocarbon and then oxygen-containing intermediates and thereby generated CO and CO(2) as the only carbon-containing products.

Journal Article↗
PubMed2001

Chlorinated ethyl and isopropyl phosphoric acid triesters in the indoor environment--an inter-laboratory exposure study.

The chlorinated organo-phosphate triesters, tris(2-chloroethyl)-phosphate (TCEP) and tris(monochloroisopropyl)-phosphate (TCPP), are employed in consumer articles for indoor usage, e.g. flame retardants and plasticizers in foam material as well as in paints, varnishes and wallpapers. As a result of this widespread usage, employing domestic dust as a matrix, both chemicals have been detected in the indoor environment. TCEP was present in 85% of a total of 983 samples, whereas TCPP was found in 60-90% of 436 cases (with levels ranging from 0.1 to 375 mg/kg). Since TCEP and TCPP residues in domestic dust are assumed to be condensates arising from primary sources, spot check analysis of various indoor materials was performed. The results show that soft foams, paints and wallpapers contained mainly TCEP, whereas in insulation and sealant foams high levels of TCPP were found. Moreover, TCEP can also be detected in indoor air in concentrations up to 6,000 ng/m3. On the basis of this data, we estimated the levels of indoor exposure via oral and inhalative ingestion.

Air Pollution, Indoor↗
PubMed1972

Phosphoric acid triester glutathione alkyltransferase. A mechanism for the detoxification of dimethyl phosphate triesters.

1. 2-Chloro-1-(2,4,5-trichlorophenyl)vinyl dimethyl phosphate (tetrachlorvinphos) is demethylated by mammalian liver supernatant (100000g) protein in the presence of GSH. 2. GSH acts as an acceptor of the transferred methyl group to form S-methyl glutathione. 3. The enzyme that catalyses this reaction is present in the soluble fraction of liver from mouse, rat, rabbit and pig at similar activity. The enzyme was purified 45-fold from pig liver, dimethyl 1-naphthyl phosphate being used as assay substrate. 4. Methyl groups are readily removed from most of the substrates studied; ethyl groups are removed at one-fiftieth to one-hundredth of the rate for methyl groups. It is likely that the enzyme plays an important role in the detoxification of the phosphate triester pesticides containing CH(3)-O-P groups.

Animals↗