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Biomedical subjects

G R Gray

Publications and source records attributed to G R Gray.

At least 19 recordsLinked to original sources
PubMed2006

Acclimation to temperature and irradiance modulates PSII charge recombination.

Acclimation of wild type and the chlorina F2 mutant of barley to either high light or low temperature results in a 2- to 3-fold increase in non-photochemical quenching which occurred independently of either energy-dependent quenching (qE), xanthophyll cycle-mediated antenna quenching or state transitions. Results of in vivo thermoluminescence measurements used to address this conundrum indicated that excitation pressure regulates the temperature gap for S(2)Q(B)(-) and S(2)Q(A)(-) charge recombinations within photosystem II reaction centers. This is discussed in terms of photoprotection through non-radiative charge recombination.

Acclimatization↗
PubMed2004

Mitochondria/nuclear signaling of alternative oxidase gene expression occurs through distinct pathways involving organic acids and reactive oxygen species.

Cultured cells of tobacco (Nicotiana tabacum L. cv Petit Havana) were used to investigate signals regulating the expression of the "model" nuclear gene encoding the alternative oxidase (AOX) (AOX1), the terminal oxidase of the mitochondrial alternative respiratory pathway. Several conditions shown to induce AOX1 mRNA accumulation also result in an increase in cellular citrate concentrations, suggesting that citrate and/or other tricarboxylic acid (TCA) cycle intermediates may be important signal metabolites. In addition, mitochondrial reactive oxygen species (ROS) production has recently been shown to be a factor mediating mitochondria-to-nucleus signaling for the expression of AOX1. We found that the exogenously supplied TCA cycle organic acids citrate, malate and 2-oxoglutarate caused rapid and dramatic increases in the steady-state level of AOX1 mRNA at low, near physiological concentrations (0.1 mM). Furthermore, an increase in AOX1 induced by the addition of organic acids occurs independently of mitochondrial ROS formation. Our results demonstrate that two separate pathways for mitochondria-to-nucleus signaling of AOX1 may exist, one involving ROS and the other organic acids.

Cell Nucleus↗
PubMed2000

Authentic standards for the reductive-cleavage method. The positional isomers of partially methylated and acetylated or benzoylated methyl 2-(acetylmethylamino)-2-deoxy-beta-D-glucopyranoside.

Described herein is the synthesis of eight positional isomers of methylated and acetylated or benzoylated methyl 2-(acetylmethylamino)-2-deoxy-beta-D-glucopyranoside. The compounds were generated simultaneously from methyl 2-(acetylmethylamino)-2-deoxy-beta-D-glucopyranoside by sequential partial methylation and benzoylation and isolated in pure form by high-performance liquid chromatography (HPLC). The desired acetates were obtained by debenzoylation and acetylation of the pure isomers. Reported herein are the 1H NMR spectra of the benzoates and the electron-ionization mass spectra of the acetates and the tri-O-methyl derivative. Also reported for the acetates and the tri-O-methyl derivative are their linear temperature-programmed gas-liquid chromatography (GLC) retention indices on three different capillary columns.

Acetates↗
PubMed2000

Authentic standards for the reductive-cleavage method. The positional isomers of partially methylated and acetylated or benzoylated 1,5-anhydroribitol.

The eight positional isomers of methylated and benzoylated 1,5-anhydroribitol were generated simultaneously from 1,5-anhydroribitol by sequential partial methylation and benzoylation, and the four meso isomers and two enantiomeric pairs of isomers so-formed were isolated in chemically pure form by high-performance liquid chromatography. The corresponding acetates were obtained by debenzoylation of the pure isomers and acetylation. Reported herein are the 1H NMR spectra of the benzoates and the electron-ionization mass spectra of the acetates and the tri-O-methyl derivative. Also reported for the acetates and the tri-O-methyl derivative are their linear temperature-programmed gas-liquid chromatography retention indices on three different capillary columns.

Acetylation↗
PubMed2000

Isolation and characterization of the cell-surface polysaccharides of Porphyromonas gingivalis ATCC 53978.

The cell-surface carbohydrates of Porphyromonas gingivalis strain ATCC 53978 were isolated and partially characterized. Three separate polysaccharides were found to be present: an extracellular polysaccharide, capsular polysaccharide and lipopolysaccharide. The capsular polysaccharide, which had peculiar, gel-like viscoelastic properties, was found to be comprised of mannuronic acid, glucuronic acid, galacturonic acid, galactose, and 2-acetamido-2-deoxy-D-glucose in relative molar ratios of 0.6:0.9:0.5:0.5:1.0, respectively. The extracellular polysaccharide was found to contain mannose, rhamnose, glucose, galactose, and 2-acetamido-2-deoxy-D-glucose in relative molar ratios of 13.5:1.4:1.0:2.0:1.0, respectively. The lipopolysaccharide was found to contain an O-antigen with a regular tetrasaccharide repeat unit comprised of 4-linked alpha-L-rhamnopyranosyl, 6-linked alpha-D-glucopyranosyl, 3-linked alpha-D-galactopyranosyl, and 4-linked 2-acetamido-2-deoxy-beta-D-glucopyranosyl residues in equimolar proportions.

Chromatography, Gas↗
PubMed2000

Family practice career attrition, 1969 to 1993: a comparison of 336 civilian and military graduates of one medical school.

Instability of specialty choice and career after initial residency entry will affect health personnel projections. Military physicians may differ from civilian physicians in their specialty choice behaviors during their careers. A cohort of 336 graduates who chose family medicine residency training was identified from the graduating classes of 1969 through 1993 at a large private medical school. Current specialty identification was determined, and attrition from family medicine was computed. As of 1997, 275 graduates (82%) were still in family medicine careers, defined by American Academy of Family Physicians membership or current American Board of Family Practice certification. Of graduates who entered military programs, 22 of 77 (28%) had left family medicine careers; 39 of 259 (15%) of the graduates who entered civilian programs had left. This difference was statistically significant (p = 0.007). Family medicine career retention is lower for males in military programs compared with males in civilian programs or females in military programs.

Career Choice↗
PubMed1998

Authentic standards for the reductive-cleavage method: the positional isomers of partially methylated and acetylated or benzoylated 1,5-anhydro-L-arabinitol.

Described herein is the synthesis of the eight positional isomers of methylated and acetylated or benzoylated 1,5-anhydro-L-arabinitol. The compounds were generated simultaneously from 1,5-anhydro-L-arabinitol by sequential partial methylation and benzoylation and isolated in pure from by high-performance liquid chromatography. The desired acetates were obtained by debenzoylation and acetylation of the pure isomers. Reported herein are the 1H NMR spectra of the benzoates and the electron-ionization mass spectra of the acetates and the tri-O-methyl derivative. Also reported for the acetates and the tri-O-methyl derivative are their linear temperature-programmed gas-liquid chromatography retention indices on three different capillary columns.

Acetylation↗
PubMed1998

Temperature/light dependent development of selective resistance to photoinhibition of photosystem I.

Exposure of winter rye leaves grown at 20 degrees C and an irradiance of either 50 or 250 micromol m(-2) s(-1) to high light stress (1600 micromol m(-2) s(-1), 4 h) at 5 degrees C resulted in photoinhibition of PSI measured in vivo as a 34% and 31% decrease in deltaA820/A820 (P700+). The same effect was registered in plants grown at 5 degrees C and 50 micromol m(-2) s(-1). This was accompanied by a parallel degradation of the PsaA/PsaB heterodimer, increase of the intersystem e- pool size as well as inhibition of PSII photochemistry measured as Fv/Fm. Surprisingly, plants acclimated to high light (800 micromol m(-2) s(-1)) or to 5 degrees C and moderate light (250 micromol m(-2) s(-1)) were fully resistant to photoinhibition of PSI and did not exhibit any measurable changes at the level of PSI heterodimer abundance and intersystem e- pool size, although PSII photochemistry was reduced to 66% and 64% respectively. Thus, we show for the first time that PSI, unlike PSII, becomes completely resistant to photoinhibition when plants are acclimated to either 20 degrees C/800 micromol m(-2) s(-1) or 5 degrees C/250 micromol m(-2) s(-1) as a response to growth at elevated excitation pressure. The role of temperature/light dependent acclimation in the induction of selective tolerance to PSI photoinactivation is discussed.

Chloroplasts↗
PubMed1997

Reductive cleavage of the positional isomers of benzoylated and methylated methyl alpha-D-mannopyranoside.

The four O-benzoyl-tri-O-methyl positional isomers, the six di-O-benzoyl-di-O-methyl positional isomers, the four tri-O-benzoyl-O-methyl positional isomers, and the tetra-O-benzoyl derivative of methyl alpha-D-mannopyranoside were synthesized, characterized, and subjected to reductive cleavage in the presence of triethylsilane and trimethylsilyl trifluoromethanesulfonate. The reactions were monitored by 1H NMR spectroscopy in order to establish the rates of the reactions and the identities of the products so formed. The tetra-O-benzoyl derivative, all tri-O-benzoyl-O-methyl positional isomers, and the 2.4-di-O-benzoyl-3.6-di-O-methyl positional isomer were fully stable to reductive-cleavage conditions, but the other di-O-benzoyl-di-O-methyl positional isomers and all O-benzoyl-tri-O-methyl positional isomers were converted to their respective 1.5-anhydro-D-mannitol derivatives via reductive cleavage of their anomeric carbon-oxygen bonds. For the mono-O-benzoyl positional isomers, the rate of reductive cleavage decreased in the order 2-O-benzoyl > 6-O-benzoyl > 3-O-benzoyl approximately 4-O-benzoyl. Moreover, all mono-O-benzoyl positional isomers were cleaved at a much faster rate than the di-O-benzoyl positional isomers. These results suggest that both anchimeric assistance and inductive effects of the ester groups contribute to the observed reaction rate. Based upon these results it is suggested that reductive cleavage of benzoylated polysaccharides might serve as a means to cleave selectively at branched residues.

Benzoates↗
PubMed1997

Reductive cleavage of permethylated polysaccharides with borane-methyl sulfide complex and butyltin trichloride.

Several per-O-methylated monosaccharides and polysaccharides were used as models in an attempt to identify more convenient reagents for accomplishing reductive cleavage of glycosidic linkages. Included in the model studies were methyl alpha- and beta-D-glucopyranoside, methyl alpha- and beta-D-mannopyranoside, and methyl alpha- and beta-D-ribofuranoside. These studies led to the identification of a new promoter, butyltin trichloride, for carrying out reductive cleavage when borane-methyl sulfide complex was used as the reducing agent. These reagents were found to accomplish the reductive cleavage of per-O-methylated amylose, cellulose, and pullulan to give only the expected derivatives of 1,5-anhydro-D-glucitol. These reagents also accomplished reductive cleavage of per-O-methylated insulin to give only the expected derivatives of 2,5-anhydro-D-mannitol and 2,5-anhydro-D-glucitol. Reductive cleavage using these reagents is easy to perform, and subsequent acetylation of the products is readily accomplished in situ.

Amylose↗
PubMed1996

Mechanism of anomerization of cyclohexyl 2-deoxy-3,4,6-tri-O-methyl-2-(N-methylacetamido)-alpha- and beta-D-hexopyranosides under reductive-cleavage conditions.

The fully methylated cyclohexyl glycosides of 2-acetamido-2-deoxy-alpha- and beta-D-hexopyranoses having the gluco, manno, and galacto configurations were each subjected to reductive-cleavage conditions using one of three promoters, namely trimethylsilyl trifluoromethanesulfonate, a mixture of trimethylsilyl methanesulfonate and boron trifluoride etherate, or boron trifluoride etherate alone. As expected, the fully methylated 1,2-trans-linked acetamido sugar derivatives were rapidly converted to their respective oxazolinium ions with all three promoters. Surprisingly, however, the fully methylated 1,2-cis-linked acetamido sugar derivatives were also converted to their respective oxazolinium ions, albeit at a much slower rate. In the latter case, evidence was obtained for anomerization to the 1,2-trans-linked isomers under reductive-cleavage conditions. Since the anomerization was relatively slow at room temperature in dichloromethane, a modified procedure was developed in which the reaction was carried out at 70 degrees C in 1,2-dichloroethane. Using the modified procedure, all 1,2-cis- and 1,2-trans-linked acetamido sugar derivatives were rapidly converted into their respective oxazolinium ions and subsequent quenching of the reactions with anhydrous methanol gave the respective 1,2-trans-linked methyl glycoside derivatives in quantitative yield. The modified procedure is recommended for the total reductive cleavage of polysaccharides comprised of acetamido sugar residues.

Acetylgalactosamine↗
PubMed1996

Structural identification of a major mitogenic lipid derived from Bacillus subtilis as a glycerophosphoglycolipid.

Lipids extracted from Bacillus subtilis using a 2:1 mixture of chloroform and methanol have been found to be very mitogenic. These lipids were fractionated on a silica column and eluted with chloroform, acetone, and 60% methanol in chloroform, and the mitogenic activity was recovered in the last fraction. Further purification of the mitogenic components was achieved by HPLC on an amino-isopropyl bonded-phase column using a linear gradient of 5-20 mM ammonium acetate in a mobile phase consisting of hexane, 2-propanol, methanol, and water (5.5:8:1.5:1). Two major and several minor mitogenic peaks were observed. One major mitogenic lipid was isolated in pure form and structurally characterized by chemical degradation analysis, NMR spectroscopy, and mass spectrometry. Mild acid hydrolysis of the lipid released glycerol phosphate and a neutral glycolipid. Saponification of the lipid released a water-soluble head group and C14-C17 branched fatty acids. Total acid hydrolysis of the head group revealed the presence of glycerol and glucose in a ratio of 1:1. Mild acid hydrolysis of the head group to remove the glycerol phosphate produced a neutral partial head group. The partial head group was methylated and then analyzed by GLC-CIMS and by the reductive-cleavage method, which revealed that it was composed of nonreducing terminal glucopyranosyl, 6-linked glucopyranosyl, and 3-linked glycerol residues in equimolar proportions. Finally, the molecular weight of the permethylated head group, obtained by fast atom bombardment mass spectrometry, was 724.3340, which is consistent with the composition of two glucose residues, one glycerol residue, and one glycerol phosphate residue. On the basis of all these results, the intact mitogenic lipid was identified as 1,2-di-O-acyl-3-O-[6-(sn-glycerol-phospho)-beta-D-glucopyranosyl-(1-->6) - beta-D-glucopyranosyl]glycerol. The purified glycolipid possessed very potent mitogenic activity in a murine splenocyte proliferation assay at a concentration of 0.01-0.1 microgram/mL.

Animals↗
PubMed1995

Reductive cleavage of glycosides with borane complexes in the presence of boron trifluoride etherate.

Mixtures consisting of five equivalents each of borane.methyl sulfide and boron trifluoride etherate per equivalent of acetal or five equivalents of various amine-borane complexes and 10 equivalents of boron trifluoride etherate readily accomplished reductive cleavage of the glycosidic linkages of several per-O-methylated monosaccharides and polysaccharides. In all cases, the expected products were obtained in the expected molar proportions and no artifactual products were observed. Reductive-cleavage analysis using these reagents is particularly convenient because the reagents themselves are easy to handle and because subsequent acetylation of the products is accomplished in situ.

Acetylation↗
PubMed1995

Authentic standards for the reductive-cleavage method. The positional isomers of partially methylated and acetylated or benzoylated 1,4-anhydro-D-xylitol.

Described herein is a general method for the synthesis of all positional isomers of methylated and acetylated or benzoylated 1,4-anhydro-D-xylitol. The benzoates are generated simultaneously from 1,4-anhydro-D-xylitol by sequential partial methylation and benzoylation or sequential partial benzoylation and methylation. The individual isomers are obtained in pure form by high-performance liquid chromatography. Debenzoylation and acetylation provided the corresponding acetates. The 1H NMR spectra of the benzoates and the electron ionization mass spectra of the acetates and the tri-O-methyl derivative are reported herein as are the linear temperature programmed gas-liquid chromatography retention indices of the acetates and the tri-O-methyl derivative on three different capillary columns.

Acetates↗
PubMed1995

Synthesis and characterization of authentic standards for the reductive-cleavage method. The positional isomers of partially methylated and acetylated or benzoylated 1,4-anhydro-L-fucitol.

Described herein is the synthesis of all positional isomers of methylated and acetylated or benzoylated 1,4-anhydro-L-fucitol. The benzoates are generated simultaneously from 1,4-anhydro-L-fucitol by sequential partial methylation and benzoylation or sequential partial benzoylation and methylation. The individual isomers are obtained in pure form by high-performance liquid chromatography. Debenzoylation and acetylation provided the corresponding acetates. The 1H NMR spectra of the benzoates and the electron-ionization mass spectra of the acetates and the tri-O-methyl derivative are reported herein as are the linear temperature programmed gas-liquid chromatography retention indices of the acetates and the tri-O-methyl derivative on three different capillary columns.

Acetates↗
PubMed1995

Authentic standards for the reductive-cleavage method. The positional isomers of partially methylated and acetylated or benzoylated 1,5-anhydro-D-mannitol.

Described herein is an efficient method for the synthesis of the sixteen positional isomers of methylated and acetylated or benzoylated 1,5-anhydro-D-mannitol. The compounds are generated simultaneously by partial methylation of 1,5-anhydro-D-mannitol and subsequent benzoylation, and the individual isomers are obtained in pure form by high-performance liquid chromatography. Debenzoylation of the latter and acetylation yielded the desired acetates. The the benzoates and the electron-ionization mass spectra of the acetates and the tetra-O-methyl derivative are reported herein as are the linear temperature-programmed gas-liquid chromatography retention indices of the acetates and the tetra-O-methyl derivative on three different capillary columns.

Acetates↗