Biomedical subjects

W W Epstein

Publications and source records attributed to W W Epstein.

13 recordsLinked to original sources

PubMed2002

The monoterpenes of Artemisia tridentata ssp. vaseyana, Artemisia cana ssp. viscidula and Artemisia tridentata ssp. spiciformis.

Monoterpenes from three different members of the Anthemideae family, Artemisia tridentata ssp. vaseyana, Artemisia cana ssp. viscidula and Artemisia tridentata ssp. spiciformis were isolated and their structures determined using spectroscopic techniques. A total of 26 irregular and regular monoterpenes were identified. Among these, 20 had previously been identified in the Anthemideae family. Of the remaining six, four were known, but previously unidentified in this family. 2,2-Dimethyl-6-isopropenyl-2H-pyran, 2,3-dimethyl-6-isopropyl-4H-pyran and 2-isopropenyl-5-methylhexa-trans-3,5-diene-1-ol were isolated from both A. tridentata ssp. vaseyana and A. cana ssp. viscidula. The irregular monoterpene 2,2-dimethyl-6-isopropenyl-2H-pyran has a carbon skeleton analogous to the biologically important triterpene squalene. Two additional irregular monoterpenes, artemisia triene and trans-chrysanthemal were isolated from A. cana ssp. viscidula and lavandulol was isolated from A. tridentata ssp. spiciformis. This is the first time a compound possessing a lavandulyl-skeletal type has been found in the Anthemideae family.

Artemisia↗

PubMed1994

Thioprenols as hydrazinolysis products of prenylated proteins: dependence upon methylation of the prenylcysteine.

When prenylated proteins are treated with hydrazine at elevated temperatures, a substantial fraction of the prenylcysteines are cleaved at the C-S bond of the beta-carbon of cysteine. Thioprenols, the initial products of this reaction, are then reduced, over time, to hydrocarbons. This elimination reaction is favored several fold if the prenylcysteine is present as a carboxylate derivative rather than as a carboxyl terminal free amino acid. Thus, the pattern of elimination has the potential for detecting substitution (methylation) of prenylcysteines. In addition, the formation of thioprenols leads to more sensitive ways for determination of the prenylcysteines.

Animals↗

PubMed1993

Differential prenylation of proteins as a function of mevalonate concentration in CHO cells.

The incorporation of [5-3H]mevalonate into prenylated proteins and polyisoprenoid lipids has been determined as a function of mevalonate concentration in Chinese hamster ovary (CHO) cells that are inhibited in mevalonate synthesis. The relative incorporation of mevalonate into the different end products of isoprenoid metabolism was markedly dependent upon the concentration of mevalonate in the medium. The synthesis of cholesterol was dominant at higher concentrations of mevalonate while higher molecular weight isoprenoids were favored at the lower concentrations. The relative incorporation of mevalonate into the different prenylcysteines of prenylated proteins was dependent upon mevalonate concentration with geranylgeranylcysteine being the principal product at higher concentrations. At low levels of mevalonate farnesylcysteine synthesis predominated and geranylcysteine was detected. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of proteins from CHO cells that had been radiolabeled at different concentrations of [3H]mevalonate had different patterns on fluorography with relatively few proteins labeled at low concentrations. A study of this effect on the prenylcysteines of a specific protein, Ras, showed considerably less sensitivity to mevalonate concentration than bulk protein. These results indicate that the specific proteins that are prenylated depend upon the availability of the isoprenyl diphosphate substrates.

Animals↗

PubMed1991

Quantitation of prenylcysteines by a selective cleavage reaction.

The allylic thioether bond of the prenylcysteines of prenylated proteins has been shown to be cleaved by 2-naphthol under alkaline conditions to yield substituted naphthopyrans. These products are readily resolved from interfering materials by HPLC and have a strongly absorbing chromophore. Thus, this reaction is suitable for quantitative analysis of prenyl substituents of proteins, and we have examined a number of tissues for their content of prenylcysteines. These amino acids are present in mammalian tissues at a concentration of 0.36-1.4 nmol/mg of protein, with a ratio of geranylgeranylcysteine to farnesylcysteine in the range of 4 to 10. Prenylcysteines were also found in the cytosolic fraction of two mouse tissues at about one-third the concentration of the whole organ. The level of these modified amino acids was found to be significantly less in a yeast, a fungus, a brown alga, a higher plant, and an insect. Again, geranylgeranylcysteine is predominant. Prenylcysteines were absent from Escherichia coli but present in an archaebacterium. The prenylcysteine content of mammalian tissue is about 1% of that of cholesterol and about equal to that of ubiquinones and dolichols. Calculations indicate that about 0.5% of all proteins are prenylated.

3T3 Cells↗

PubMed1990

Prenylated proteins: the structure of the isoprenoid group.

The mevalonate-derived portion of a prenylated protein from Chinese hamster ovary cells has been established as diterpenoid (C20). This group is linked to a carboxyl-terminal cysteine as a thioether. It was removed from the protein by hydrazinolysis followed by Raney nickel desulfurization, and the resulting hydrocarbon fraction was analyzed by gas chromatography-mass spectrometry.

Animals↗

PubMed1990

Prenylated proteins: synthesis of geranylgeranylcysteine and identification of this thioether amino acid as a component of proteins in CHO cells.

Prenylated proteins, labeled in the isoprenoid residue by growing CHO cells in medium containing [5-3H]mevalonate, were degraded by three different proteolytic procedures, enzymatic or alkaline hydrolysis as well as hydrazinolysis. The products thus obtained were analyzed by HPLC with chemically prepared all-trans-geranylgeranylcysteine as a standard. About 10% of the radioactive products released by each lytic procedure showed the same chromatographic properties as geranylgeranylcysteine. This verifies the earlier conclusion, based on less-direct evidence, that this thioether derivative of cysteine is a component of naturally occurring proteins. The finding of this modified amino acid as a product of hydrazinolysis indicates that it is a carboxyl-terminal amino acid and that it is not carboxyl-methylated.

Animals↗

PubMed1989

Prenylated proteins: demonstration of a thioether linkage to cysteine of proteins.

Prenylated amino acid fragments have been isolated from prenylated proteins of Chinese hamster ovary cells. Gel-exclusion chromatography indicates that these proteins are modified by two different prenyl groups. The prenyl-amino acid fragments are labeled by 35S from cysteine, and this bond is cleaved by Raney-Ni, proving that the prenyl residue is linked to protein via a thioether to cysteine. Hydrazinolysis has been used to demonstrate that the cysteine is carboxy terminal.

Animals↗

PubMed1982