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R Kerssebaum

Publications and source records attributed to R Kerssebaum.

5 recordsLinked to original sources
PubMed2001

Separation of structural components in soil organic matter by diffusion ordered spectroscopy.

Diffusion ordered spectroscopy (DOSY) was applied to two extracts of organic matter from the surface horizon of an oak forest soil. It was possible to identify and confirm the presence of numerous aliphatic, aromatic, sugar, and amino acid components that could be separated on the basis of diffusion in DMSO-d6 and D2O. On average, sugar components were identified as the largest molecules in solution, with molecular masses up to approximately 1500 Da followed by the aliphatic and aromatic components. Amino acids with a range of molecular weights were also identified in the mixture. The summation of the individual slices from the DOSY experiment closely resembles the conventional 1H spectra of the material, indicating that the components identified with DOSY represent all the components present in the mixture. The separation of components in the mixture in organic solvent supports new findings that fulvic and humic acids are not cross-linked, high molecular weight macromolecules but are instead aggregates composed of relatively simple molecules that take on colloidal properties in the presence of metal ions in aqueous solution. Using the knowledge that these organic mixtures are combinations of relatively simple entities with well-documented reactivities and behavior will improve our ability to predict and model their interactions and fate under natural conditions.

Amino Acids↗
PubMed1994

Role of P4502E1 in the metabolism of 1,1,2,2-tetrafluoro-1-(2,2,2-trifluoroethoxy)-ethane.

1. The metabolism of 1,1,2,2-tetrafluoro-1-(2,2,2-trifluoroethoxy)-ethane (HFE), a prospective chlorofluorocarbon alternative, was studied in rat and human liver microsomes and in rat in vivo. 2. HFE was metabolized to inorganic fluoride, trifluoroacetaldehyde hydrate, trifluoroacetic acid and difluoroacetic acid, which were identified by 19F-nmr in microsomal incubation. After i.p. dosing with 200 mg/kg HFE to rat, trifluoroacetic acid and trifluoroacetaldehyde hydrate were identified as urinary metabolites. 3. The formation of inorganic fluoride from HFE was used to quantify oxidative metabolism. In liver microsomes from untreated rat, formation of inorganic fluoride could not be detected. However, microsomes from rats treated with P4502E1 (2E1) inducers ethanol and pyridine catalysed the formation of fluoride at different rates. The extent of fluoride formation in microsomes correlated with the amount of 2E1 protein as determined by immunoblots with a polyclonal antibody and with the extent of oxidation of p-nitrophenol and chlorzoxazone, two specific substrates for 2E1. 4. In different samples of human liver microsomes, the formation of inorganic fluoride correlated well with the ability of the microsomes to oxidize chlorzoxazone and p-nitrophenol and the amount of 2E1 protein as determined by immunoblots. 5. The obtained results suggest that 2E1 plays a major role in the metabolism of HFE in rat and man.

Animals↗
PubMed1993

Fluorinated vitamin b(12) analogs are cofactors of corrinoid-dependent enzymes: a f-labeled nuclear magnetic resonance probe for identifying corrinoid-protein interactions.

The homoacetogenic bacterium Sporomusa ovata synthesized the vitamin B(12) analog phenolyl cobamide or 4-fluorophenolyl cobamide when the methanol medium of growing cells was supplemented with 10 mM phenol or 5 mM 4-fluorophenol. Phenol and, presumably, 4-fluorophenol were specifically incorporated into these cobamides, since phenol was not metabolized significantly into amino acids or into acetic acid, the product of the catabolism. The phenol-containing cobamides contributed up to 90% of the protein-bound cobamides of the 1,300 to 1,900 nmol of corrinoid per g of dry cell material formed. Fluorine-19 nuclear magnetic resonance spectroscopy of 4-fluorophenolyl cobamide exhibited a resonance near 30 ppm. An additional signal emerged at 25 ppm when 4-fluorophenolyl cobamide was investigated as the cofactor of a corrinoid-dependent protein. The two resonances indicated distinct cofactor arrangements within the protein's active site. A 5-ppm high-field shift change suggested van der Waal's interactions between the fluorinated nucleotide of the cofactor and adjacent amino acid residues of the enzyme. Similarly, Propionibacterium freudenreichii and Methanobacterium thermoautotrophicum synthesized 5-fluorobenzimidazolyl cobamide. The human corrinoid binders intrinsic factor, transcobalamin, and haptocorrin recognized this corrinoid like vitamin B(12). Hence, it is possible to use F-labeled nuclear magnetic resonance spectroscopy for analyses of protein-bound cobamides.

Journal Article↗
PubMedDate not supplied

Role of cytochrome P450 2E1 in the metabolism of 1,1,2,3,3,3-hexafluoropropyl methyl ether.

1,1,2,3,3,3-Hexafluoropropyl methyl ether is developed as an alternative to replace ozone-depleting chlorofluorocarbons. The metabolism of 1,1,2,3,3,3-hexafluoropropyl methyl ether was studied in rat and human liver microsomes and in rats in vivo. Rat and human liver microsomes metabolized 1,1,2,3,3,3-hexafluoropropyl methyl ether to inorganic fluoride and formaldehyde in a ratio of 2:1. 2,3,3,3-Tetrafluoropropionic acid was also identified as a metabolite by GC/MS and 19F-NMR. In rat liver microsomes, formation of inorganic fluoride and formaldehyde from 1,1,2,3,3,3-hexafluoropropyl methyl ether was dependent on the presence of NADPH, time, substrate concentration and protein concentration, and was linear for up to 35 min. Microsomes from unpretreated rats oxidized 1,1,2,3,3,3-hexafluoropropyl methyl ether at low rates (3.56 nmol fluoride.20 min-1.mg-1). Pretreatment of rats with pyridine and ethanol, inducers of cytochrome P450 2E1, increased the rate of fluoride formation. The rates of fluoride formation from 1,1,2,3,3,3-hexafluoropropyl methyl ether correlated well with the relative amount of cytochrome P450 2E1 in the microsomes as quantified by immunoblotting. Coincubation of 1,1,2,3,3,3-hexafluoropropyl methyl ether with microsomes and diethyldithiocarbamate (100 microM), an inhibitor of cytochrome P450 2E1, reduced fluoride production by > 80%. In different samples of human liver microsomes, rates of fluoride formation were higher than observed in liver microsomes from unpretreated rats and correlated well to the content of cytochrome P450 2E1 protein as determined by immunoblotting and chlorzoxazone 6-hydroxylation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗