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Biomedical subjects

R L Lester

Publications and source records attributed to R L Lester.

At least 55 records · Page 3Linked to original sources
PubMed1986

Characterization of inositol lipids from Leishmania donovani promastigotes: identification of an inositol sphingophospholipid.

Inositol lipids account for 15% of the total cellular phospholipids of Leishmania donovani promastigotes. Four major inositol lipids were identified and characterized: phosphatidylinositol (PI), phosphatidylinositol phosphate (PI-P), phosphatidylinositol diphosphate (PI-P2), and an inositol sphingophospholipid (InSL). Diacyl and alkyl acyl PI were identified. The major esterified fatty acids of PI, PI-P, and PI-P2 were similar and unlike those of mammalian inositol glycerolipids. Leishmania inositol glycerolipids contained only trace amounts of arachidonic acid; the major species were C16 and C18 acids. The InSL comprised about 40% of the inositol lipids. The amide-linked fatty acids of InSL were mainly C16 and C18 acids. Differential hydrolysis and nuclear magnetic resonance spectrometry indicated that the InSL had a phosphoryl bond. The major long chain bases of the InSL were identified by gas-liquid chromatography and high resolution mass spectrometry as straight chain C16 and C18 sphingosines. The finding of InSL in Leishmania is of interest because InSL have previously been found only in plants and fungi. Metabolic radiolabeling experiments suggest that this lipid may be a precursor of an antigenic cell surface membrane lipophosphoglycan which is shed into the culture medium by the organism.

Animals↗
PubMed1984

Occurrence of novel antigenic phosphoinositol-containing sphingolipids in the pathogenic yeast Histoplasma capsulatum.

Five alkali-stable lipids from the yeast phase of Histoplasma capsulatum have been purified and analyzed. Each compound has equimolar amounts of hydroxysphinganine (phytosphingosine) and a hydroxy or nonhydroxy 24:0 fatty acid. All yield inositol phosphate after acid hydrolysis, and several are novel in that they also yield dimannosylinositol (compound V) and isomeric galactosyldimannosylinositols (compounds VI and VIII) after strong ammonolysis. The foregoing as well as other data suggest that compound V is a dimannosylinositolphosphoceramide and compounds VI and VIII are galactosyldimannosylinositolphosphoceramides with isomeric head groups. The chromatographic behavior of compounds II and III indicates that they are similar to the inositolphosphoceramides previously observed in Saccharomyces cerevisiae. Compounds V and VI are virtually absent from the mycelial phase of H. capsulatum. Antibodies that react with compounds V, VI, and VIII have been detected in sera from patients with histoplasmosis.

Antibody Specificity↗
PubMed1984

Carbohydrate structures of three novel phosphoinositol-containing sphingolipids from the yeast Histoplasma capsulatum.

From the yeast phase of the human pathogen Histoplasma capsulatum, three novel glycolipids were isolated, shown to react with sera from histoplasmosis patients, and partially characterized: compound V, ceramide-P-inositol-[mannose2]; compound VI, ceramide-P-inositol-[mannose2, galactose]; compound VIII, an isomer of compound VI [Barr, K., & Lester, R.L. (1984) Biochemistry (preceding paper in this issue)]. Ammonolysis of these lipids has yielded all the carbohydrate (oligosaccharides V, VI, and VIII) as novel, intact oligosaccharides suitable for characterization. Anomeric configurations were determined by specific glycosidase digestion and by the stability of peracetylated saccharides to CrO3 oxidation. Linkages were established by methylation analysis. These experiments yielded the following structural assignments: (formula; see text) The occurrence of galactofuranose is novel for glycosphingolipids, and it is noteworthy that compound VI is immunoreactive.

Carbohydrate Conformation↗
PubMed1984

Characterization of the extracellular bactericidal factors of rat alveolar lining material.

The surfactant fraction (55,000-g pellet) of leukocyte-free rat bronchoalveolar lavage fluid contains factors that rapidly kill and lyse pneumococci. These factors were purified and identified biochemically by using a quantitative bactericidal test to monitor fractionation procedures. 91% of the antipneumococcal activity of rat surfactant was recovered in chloroform after extraction of rat surfactant with chloroform-methanol (Bligh-Dyer procedure). After chromatography on silicic acid with chloroform, acetone, and methanol, all detectable antibacterial activity (approximately 80% of the initial activity) eluted with the neutral lipids in chloroform. When rechromatographed on silicic acid with hexane, hexane-chloroform, and chloroform, the antibacterial activity eluted with FFA. Thin-layer chromatography (TLC) established that the antibacterial activity was confined to the FFA fraction. Gas-liquid chromatography showed that the fatty acid fraction contained a mixture of long-chain FFA (C12 to C22) of which 66.7% were saturated and 32.4% were unsaturated. The quantity of TLC-purified FFA needed to kill 50% of 10(8) pneumococci under standardized conditions (one bactericidal unit) was 10.6 +/- 0.5 micrograms. Purified FFA acted as detergents, causing release of [3H]choline from pneumococcal cell walls and increased bacterial cell membrane permeability, evidenced by rapid unloading of 3-O-[3H]methyl-D-glucose. FFA acting as detergents appear to account for the bactericidal and bacteriolytic activity of rat pulmonary surfactant for pneumococci.

Animals↗
PubMed1983

The isolation and characterization of a mutant strain of Saccharomyces cerevisiae that requires a long chain base for growth and for synthesis of phosphosphingolipids.

A mutant of Saccharomyces cerevisiae has been obtained that shows an absolute growth requirement for long chain bases found in sphingolipids. In the absence of a long chain base, the cells are unable to synthesize the phosphoinositol-containing sphingolipids characteristic of yeast. These results suggest that one or more of the yeast sphingolipids plays a vital biological role.

Chromatography, Liquid↗
PubMed1982

Effect of inositol starvation on the in vitro syntheses of mannan and N-acetylglucosaminylpyrophosphoryldolichol in Saccharomyces cerevisiae.

An early consequence of starvation for inositol in yeast is inhibition of synthesis of the major cell wall components mannan and glucan. In looking for the mechanism of this inhibition, we found that the activity of the enzyme catalyzing the synthesis of N-acetylglucosaminylpyrophosphoryldolichol was diminished in particular membrane preparations from cells starved for inositol. This loss of reactivity was observed under a variety of in vitro assay conditions and could be restored by the addition of phosphatidylinositol but not by other phosphoinositol-containing sphingolipids known to occur in yeast. When assayed in the presence of high concentrations of Triton X-100, enzyme preparations from both control and inositol-starved cells required phosphatidylinositol for maximal activity. Since this enzyme catalyzed an early step in the synthesis of mannan that is N-linked to protein, a reasonable hypothesis is that inhibition of mannan synthesis in inositol-starved cells results from the depletion of the necessary cofactor phosphatidylinositol.

Glucosyltransferases↗
PubMed1981

Glycophosphoceramides from plants. Purification and characterization of a novel tetrasaccharide derived from tobacco leaf glycolipids.

A glycophosphoceramide concentrate prepared from tobacco leaves was shown to contain a mixture of related lipids (Kaul, K., and Lester, R. L. (1975) Plant Physiol. 55, 120-129; Kaul, K., and Lester, R. L. (1978) Biochemistry 17, 3569-3575) with the simplest and most abundant components having the structure GlcN(+/- Ac)(alpha 1 leads to 4)GlcUA(alpha 1 leads to 2)myoinositol-1-O-phosphorylceramide (Hsieh, T. C.-Y., Kaul, K., Laine, R. A., and Lester, R. L. (1978) Biochemistry 17, 3575-3579). To determine the structure of the more complex members of this series, a mixture of oligosaccharides was prepared from a carboxyl-reduced glycophosphoceramide concentrate by alkali-catalyzed hydrolysis and alkaline phosphatase treatment. A combination of reverse-phase high pressure liquid chromatography (Wells, G. B., and Lester, R. L. (1979) Anal. Biochem. 97, 184-190), normal-phase high pressure liquid chromatography, and thin layer chromatography were used to resolve several oligosaccharides as acetylated derivatives. Products of methylation analysis, CrO3 oxidation, and deacetylation-deamination were identified using chemical ionization mass spectrometry to give the following novel structures. A major tetrasaccharide was completely characterized as Gal(alpha 1 leads to 4)GlcNAc(alpha 1 leads to 4)GlcUA(alpha 1 leads to 2)myoinositol. An additional structure of a minor tetrasaccharide was partially characterized as GlcNAc(alpha 1 leads to 4)GlcUA(alpha 1 leads to ?)myoinositol(O leads from 1 alpha)Man. These are representatives of a class of acidic glycolipids from plants, possibly analogous to the acidic gangliosides found in animal cell membranes.

Carbohydrate Conformation↗
PubMed1980

Effects of inositol starvation on phospholipid and glycan syntheses in Saccharomyces cerevisiae.

The early biochemical consequences of inositol starvation in an inositol auxotroph of Saccharomyces cerevisiae were examined as a means of determining the cellular role of inositol. Upon withdrawal of inositol, the rate of incorporation of 32P-labeled inorganic phosphate into phosphatidylinositol and into the phosphoinositol-containing sphingolipids immediately dropped by 80 and 50%, respectively; however, synthesis of the other major phospholipids continued for 2 to 3 h at control rates. The incorporation of [U-14C]glucose into cell wall glycans began to decline immediately poststarvation and decreased to 50% of the initial rate by 80 min for mannan and by 140 min for alkali- and acid-insoluble glucan. These changes in the rates of synthesis of cell wall glycan and phosphatidylinositol were the earliest effects of inositol starvation, preceding inhibition of the synthesis of protein and ribonucleic acid as measured by incorporation of radioactive precursors into trichloroacetic acid-insoluble cell material. These results suggest that phosphatidylinositol may play a direct role in the synthesis or secretion of yeast glycans.

Fungal Proteins↗
PubMed1980

Biosynthesis of phosphoinositol-containing sphingolipids from phosphatidylinositol by a membrane preparation from Saccharomyces cerevisiae.

Incubation of membranes prepared from Saccharomyces cerevisiae with [32P]phosphatidyl[3H]inositol resulted in the transfer of both labels to two products which were characterized as two species of inositolphosphoceramide, differing in the ceramide portion of the molecule. The products were characterized on the basis of stability in mild alkali, mobility on silica gel-impregnated paper, chromatography on silicic acid columns, and release of inositol phosphate upon base hydrolysis. The reaction did not require the addition of metals, nor was it inhibited by ethylenediaminetetraacetic acid. The detergents Triton X-100 and Tween 20 provided little, if any, stimulation. At relatively high concentrations of phosphatidylinositol (1 to 4 mM), the in vitro rate was about 20% of the in vivo rate. Although ceramide was a logical substrate, the reaction could not be greatly stimulated by the addition of ceramides containing mono- and dihydroxy fatty acids. In addition, incubation of yeast membranes with [32P]phosphatidylinositol gave rise to a product that was chromatographically indistinguishable from the major yeast phosphosphingolipid, mannose-(inositol-P)2 ceramide.

Cations, Divalent↗
PubMed1980

The extraction of inositol-containing phospholipids and phosphatidylcholine from Saccharomyces cerevisiae and Neurospora crassa.

By use of fungi grown in the presence of [3H]-inositol and [14C]choline, we have explored methods for the quantitative extraction of inositol-containing phospholipids and phosphatidylcholine. Slightly alkaline mixtures of both ethanol-water and ethanol-diethylether-water at elevated temperatures were shown to effectively extract these lipids from intact Saccharomyces cerevisiae and Neurospora crassa. Some previously published procedures fail to completely extract to very polar phosphoinositol-containing sphingolipids of these organisms. Trichloroacetic acid can be used with caution in killing cells prior to extraction; lipid destruction can occur at elevated concentrations and temperatures. Complete extraction of these very polar lipids with polar solvents also results in an extract containing significant amounts of non-lipids.

Inositol↗
PubMed1978

Isolation of six novel phosphoinositol-containing sphingolipids from tobacco leaves.

A concentrate of phosphosphingolipids from tobacco leaves has been resolved into two groups by chromatography on diethylaminoethylcellulose. The first group eluted contains no acetyl residues, whereas the second group contains one N-acetyl/mol of phosphorus. Three lipids from each group have been purified by chromatography on Porasil columns. The chemical composition of these six novel lipids shows them to be related to the previously characterized phosphosphingolipids PSL-I, N-acetylglucosamine[glucuronic acid, inositol phosphate]ceramide and PSL-II, glucosamine[glucuronic acid, inositol phosphate] ceramide [Kaul, K.,and Lester,R. L. (1975), Plant Physiol. 55, 120]. The novel lipids are: PSL-IA, PSL-I-[Ara2Gal2]; PSL-IB, PSL-I-[Ara3Gal2]; PSL-IC, PSL-I-[Ara4Gal2]; PSL-IIA, PSL-II-[Ara3Gal]; PSL-IIB, PSL-II-[Ara2or3Gal2]; PSL-IIC, PSL-II-[Ara2Gal2Man]. The unusual finding of unacetylated hexosamine in the PSL-II group of lipids appears not to be an artifact, as suggested by experiments involving rapid harvesting and processing of the tobacco leaves. Some of the fractions obtained by chromatography on diethylaminoethylcellulose appear to contain phosphosphingolipids with 16 or more sugar residues.

Phosphatidylinositols↗
PubMed1978

Structure of a major glycophosphoceramide from tobacco leaves, PSL-I: 2-deoxy-2-acetamido-D-glucopyranosyl(alpha1 leads to 4)-D-glucuronopyranosyl(alpha1 leads to 2)myoinositol-1-O-phosphoceramide.

The chemical structure of a major glycophosphoceramide from tobacco leaves, called PSL-I [K. Kaul and R. L. Lester (1975), Plant Physiol. 55, 120], has now been characterized as 2-deoxy-2-acetamido-D-glucopyranosyl(alpha1 leads to 4)D-glucuronopyranosyl(alpha1 leads to 2)myoinositol-1-O-phosphoceramide. Sites of glycoside linkage were determined by (1) methylation analysis on a trisaccharide isolated by degradation of carboxyl-reduced PSL-I and (2) periodate oxidation experiments on PSL-I. The resulting products were identified with gas chromatography/mass spectrometry. Anomeric configurations were determined by resistance of the sugars in the peracetylated trisaccharide to chromium trioxide treatment.

Glycosphingolipids↗