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S Collin

Publications and source records attributed to S Collin.

At least 37 records · Page 2Linked to original sources
PubMed1999

Combinatorial approach to flavor analysis. 1. Preparation and characterization of a S-methyl thioester library.

A new method for the "one-pot" synthesis of S-methyl thioesters has been developed by reacting methyl chlorothiolformate with carboxylic acids. The resulting "flavor library" contained all the intended thioesters and a single major impurity, identified by GC-MS as S, S-dimethyldithiocarbonate. Quantification of individual compounds present in the library was performed by GC analysis using two independent methods of detection, SCD and FID. It was shown that apart from S-methyl thioacetate (0.8 mol %), molar concentrations of other thioesters varied in a relatively narrow range from 4.2 mol % for S-methyl thiopropionate to 14.1 mol % for S-methyl thiohexanoate. In general, medium chain S-methyl thioesters were present in slightly higher molar concentrations than those prepared from short or long chain carboxylic acids. This variation was attributed to partial loss of the most volatile components during extraction and the lower reactivity of higher homologues. The library was used for the characterization of some physicochemical parameters of thioesters. In particular, lipophilicity coefficients (log k(w)) and thioester retention in 10, 20, and 33% triolein (used as a model lipid phase) were determined directly by reverse-phase HPLC and extrapolated from the respective data. This analysis illustrates that substantial information can be generated using a library containing a relatively large number of compounds in effectively the same way as is necessary for the analysis of a single sample.

Chromatography, Gas↗
PubMed1999

Combinatorial approach to flavor analysis. 2. Olfactory investigation of a library of S-methyl thioesters and sensory evaluation of selected components.

The odor characteristics of individual components present in a library comprised of S-methyl thioesters were determined independently by two laboratories using similar but not identical techniques. The odor potency was assessed by values of best estimate-GC-lower amount detected by sniffing (BE-GC-LOADS). For small and medium chain S-methyl thioesters, these values were found to increase from 6 ng for S-methyl thiobutanoate to 90 ng for S-methyl thiostearate. All assessors detected a "green", "floral", or "pineapple" odor for S-methyl thiohexanoate and described thioesters containing a 2-6 carbon chain length as "cheesy". The results of this preliminary analysis were confirmed by a more extensive study of selected compounds, namely S-methyl thioacetate, S-methyl thiopropionate, S-methyl thiobutanoate, and S-methyl thiohexanoate, using a trained panel of 18 subjects. The subjects confirmed the presence of the "green" and "fruity" notes in the odor of S-methyl thiohexanoate. The analysis also revealed a significant difference in the odor of S-methyl thiopropionate relative to that of S-methyl thioacetate and S-methyl thiobutanoate. When "cheesy" characteristics were mentioned, the majority of panelists clearly associated the flavor of S-methyl thiopropionate with Camembert with almost 20% of all the descriptors given referring specifically to this cheese variety as compared to about 2 and 5% in the case of S-methyl thioacetate and thiobutanoate, respectively. Prompted by this observation, two samples of Camembert prepared from unpasteurized and pasteurized milk were analyzed and relatively large amounts of S-methyl thiopropionate were found in the former but not in the latter cheese. The results obtained in the course of this work suggest that the sensory analysis of combinatorial libraries is a useful new approach in the search for new commercial flavors and/or identification of characteristic flavors in foods.

Chromatography, Gas↗
PubMed1999

Release of deuterated nonenal during beer aging from labeled precursors synthesized in the boiling kettle.

The use of labeled nonenal enabled the demonstration that the appearance of the cardboard flavor in finished beer comes from lipid auto-oxidation during wort boiling and not from lipoxygenasic activity during mashing. Free trans-2-nonenal produced by linoleic acid auto-oxidation in the kettle disappears, owing to retention by wort amino acids and proteins. This binding linkage protects trans-2-nonenal from yeast reduction but is reversible, allowing release of the compound at lower pH during aging. Labeled trans-2-nonenal is detected after aging when deuterated precursors form in the boiling kettle. The amount of alkenal released correlates with the concentration of reversible associations in the pitching wort. This work brings new illumination to the formation of trans-2-nonenal and overturns many previous hypotheses. It also explains why a reduction in the beer pH intensifies the cardboard flavor.

Aldehydes↗
PubMed1999

Identification of AtPIS, a phosphatidylinositol synthase from Arabidopsis.

Phosphatidylinositol synthase is the enzyme responsible for the synthesis of phosphatidylinositol, a key phospholipid component of all eukaryotic membranes and the precursor of messenger molecules involved in signal transduction pathways for calcium-dependent responses in the cell. Using the amino acid sequence of the yeast enzyme as a probe, we identified an Arabidopsis expressed sequence tag potentially encoding the plant enzyme. Sequencing the entire cDNA confirmed the homology between the two proteins. Functional assays, performed by overexpression of the plant cDNA in Escherichia coli, a bacteria which lacks phosphatidylinositol and phosphatidylinositol synthase activity, showed that the plant protein induced the accumulation of phosphatidylinositol in the bacterial cells. Analysis of the enzymatic activity in vitro showed that synthesis of phosphatidylinositol occurs when CDP-diacylglycerol and myo-inositol only are provided as substrates, that it requires manganese or magnesium ions for activity, and that it is at least in part located to the bacterial membrane fraction. These data allowed us to conclude that the Arabidopsis cDNA codes for a phosphatidylinositol synthase. A single AtPIS genetic locus was found, which we mapped to Arabidopsis chromosome 1.

Amino Acid Sequence↗
PubMed1998

Molecular lipophilicity potential by CLIP, a reliable tool for the description of the 3D distribution of lipophilicity: application to 3-phenyloxazolidin-2-one, a prototype series of reversible MAOA inhibitors.

The capacity factor of eleven derivatives belonging to a prototype series of 3-phenyloxazolidin-2-one, reversible MAO inhibitors, was measured and compared to the calculated log Pcalc using the CLIP package. We demonstrate that this Molecular Lipophilicity Potential (MLP) approach is a valuable tool to estimate log Pcalc of such compounds.

Chromatography, High Pressure Liquid↗
PubMed1998

Floral Origin Markers of Chestnut and Lime Tree Honeys.

The apiculture industry is more and more interested in finding typical markers to authenticate floral origin of honeys. With this aim, some reliable volatile compounds were proposed to identify origin of lime tree and chestnut samples. A dichloromethane extraction followed by a Likens-Nickerson simultaneous steam distillation/solvent extraction led to representative honey extracts. About 400 volatile compounds were separated by gas chromatography, but only a few authenticated the floral origin of honeys. Chestnut honeys are distinguishable from other origins by high concentrations of acetophenone, 1-phenylethanol (>88 ppb), and 2-aminoacetophenone (>154 ppb). Lime tree honeys are characterized by enhanced amounts of shikimate pathway derivatives (ethylmethylphenol isomer (>31 ppb), 4-tert-butylphenol, estragole (>51 ppb), and p-methylacetophenone but also by high concentrations of monoterpene-derived compounds (menthol, thymol, 8-p-menthene-1,2-diol, and carvacrol (>76 ppb)) and methyl(1-methylethenyl)benzene.

Journal Article↗
PubMed1996

The two nonstructural proteins from wheat dwarf virus involved in viral gene expression and replication are retinoblastoma-binding proteins.

Tumor-inducing viruses like simian virus 40 or the human adenovirus produce oncoproteins which interfere with the cellular retinoblastoma (Rb) tumor-suppressor protein to create an appropriate molecular environment in the nucleus for viral transcription and replication. Such a strategy has been considered to be restricted to animal viruses. Here we demonstrate that plant viruses may use similar mechanisms for recruiting host factors. Wheat dwarf virus (WDV) encodes two potential nonstructural proteins, C1 and C1:C2, both containing the consensus Rb-binding motif LeuXCysXGlu that allows the oncoproteins from animal viruses to inactivate Rb. C1:C2 is a key determinant of viral replication and V(virion)-sense expression. Using a yeast two-hybrid protein assay, we demonstrate for the first time that the C1:C2 protein from WDV interacts with a retinoblastoma protein, providing an explanation for the previously observed dependence of viral replication on an intact Rb-binding motif. We also show that C1, for which no function had been demonstrated, is required for V-sense gene expression. This suggests that V-sense expression might be dependent on the interaction of C1 with Rb. Our findings provide further evidence for the presence of transforming-like proteins in a plant virus and will help to explain the production of symptoms in a plant viral infection through a mechanism mediated by a key regulator of cell cycle and differentiation.

Amino Acid Sequence↗
PubMed1995

Affinities of nutty and green-smelling pyrazines and thiazoles to odorant-binding proteins, in relation with their lipophilicity.

Thirty-two green- and/or nutty-smelling compounds, most of them pyrazine and thiazole derivatives, were tested in ligand binding assays with purified 19 kDa bovine and 22 kDa porcine olfactive binding proteins (OBPs). Unlike the nutty ones, all the green odorants were found to be good ligands for both proteins. Lipophilicity appears as an interesting discriminating physicochemical parameter, predictive of the affinity for OBPs and of the related odour profile.

Animals↗
PubMed1994

Differential screening of mitochondrial cDNA libraries from male-fertile and cytoplasmic male-sterile sugar-beet reveals genome rearrangements at atp6 and atpA loci.

As part of a strategy to define differences in genome organization and expression between cytoplasmic male-sterile (CMS) and male-fertile (MF) sugar-beet mitochondria, cDNA libraries from both mitochondrial genotypes were constructed. Preliminary screening with ribosomal RNA gene probes identified candidate cDNA clones corresponding to structural genes. In addition, reciprocal hybridization experiments were performed using labelled first-strand cDNA to identify uniquely transcribed sequences. One cDNA clone (pYC700) is unique to CMS mitochondria and is located upstream of the F0F1-ATPase subunit 6 gene (atp6). Another cDNA clone (pYC130), when used as a probe in northern hybridization analysis, revealed novel transcript profiles in CMS sugar-beet mitochondria. Sequence analysis of this cDNA showed strong homology with the F0F1-ATPase subunit alpha (atpA) coding sequences from several higher plants. The atp6 and atpA loci from each genotype were cloned and the genomic organization, DNA sequence and transcription of each locus was studied. Differences in the transcript profiles of each gene are a consequence of genomic rearrangements 5' to the coding sequence.

Amino Acid Sequence↗
PubMed1991

Evidence for the presence of hairpin chloroplast DNA molecules in barley cultivars.

Total DNA was extracted from young green and etiolated barley leaf shoots and run on 2D neutral/alkaline agarose gels. This technique showed the presence of molecules which behaved as though their single-stranded length was twice their double-stranded length. This behaviour was sensitive to S1 nuclease. Our conclusion is that these DNAs are hairpin molecules. They are homologous to sequences found throughout the barley chloroplast genome. This type of molecule is present in uncut DNA with a continuous range of sizes varying between 0.5 and 15 kbp in our experimental conditions. The origin and possible biological function of these molecules is discussed.

Blotting, Southern↗
PubMed1989

Risk factors for infant botulism in the United States.

To define risk factors for infant botulism, we performed a 2-year prospective case-control study of 68 laboratory-confirmed cases in infants living in the United States, outside of California. For each case patient, two control subjects were matched by date and hospital of birth or county birth records. By univariate analysis, breast-feeding (odds ratio = 2.9) and consumption of honey (odds ratio = 9.8) were associated with disease, but only 11 case patients (16%) had eaten honey. Decreased frequency of bowel movement (less than one per day for at least 2 months) was also associated with disease in infants 2 months of age and older (odds ratio = 5.2). Risk factors changed with the age of the patient at disease onset when analyzed by multivariate logistic regression methods. For infants less than 2 months old, living in a rural area or on a farm was the only significant risk factor (odds ratio = 6.4). For infants 2 months of age and older, breast-feeding (odds ratio = 3.8), less than one bowel movement per day for at least 2 months (odds ratio = 2.9), and ingestion of corn syrup (odds ratio = 5.2) were associated with disease. The severity of the disease was similar for breast- and bottle-fed infants. Clearly defined food exposures account for a minority of infant botulism cases. Preexisting host factors, such as intestinal flora and frequency of bowel movements, may be the most important risk factors for development of disease.

Botulism↗
PubMed1989

Structural requirements of Na+-dependent antidopaminergic agents: Tropapride, Piquindone, Zetidoline, and Metoclopramide. Comparison with Na+-independent ligands.

Molecular graphic design coupled with PCILO and crystallographic results have been used to investigate the three-dimensional structure of Tropapride, Piquindone, Zetidoline, and Metoclopramide, four dopamine D-2 receptor antagonists showing Na+-dependent binding. Three putative pharmacophoric elements, a nitrogen lone pair, a phenyl ring and a carbonyl moiety, are similarly oriented in all the Na+-dependent drugs. Conversely, for Na+-independent analogs, the two latter pharmacophoric elements play a subordinate role, but two pi-electron regions are systematically localized on the other side of the molecule: the first is a phenyl group while the second is a carbonyl function as in butyrophenones, a cyano group as in R48455, or a phenyl ring as in diphenylbutylpiperidines or tricyclics. The presence of a benzyl ring on this side in Tropapride might explain its weak extrapyramidal effects.

Computer Graphics↗
PubMed1989

The amino acid sequence of the parvalbumin from the very fast swimbladder muscle of the toadfish (Opsanus tau).

1. The parvalbumin from the very fast striated muscle of the swimbladder of the toadfish (Opsanus tau) has been purified to homogeneity and its amino acid sequence has been completely elucidated. 2. The polypeptide chain is made of 109 residues, belongs to the beta group of parvalbumins and presents characteristics common to many other parvalbumins, i.e. a blocked N-terminal group, a cysteine and an arginine residue at positions 18 and 75 respectively and a quadruplet of acidic residues in the region 59-62.

Amino Acid Sequence↗
PubMed1989

Stereoelectronic study of zetidoline, a dopamine D2 receptor antagonist.

A combination of experimental and theoretical methods were used to investigate the stereoelectronic structure of zetidoline, a dopamine D2 receptor antagonist showing Na+-dependent binding. The solid-state conformation of zetidoline is characterized by synplanarity (coplanarity of the two rings with the chloro substituent and the carbonyl group on the same side). The side chain in the crystal adopts a folded conformation which places the azetidine nitrogen atom at about 8 A from the center of the aromatic ring. Quantum mechanical calculations indicate the synperiplanar and antiperiplanar conformations of the ring system to be of approximately equal energies. The molecular electrostatic potential of zetidoline in a nearly extended conformation shows a remarkable similarity with that of orthopramides (e.g. metoclopramide) and indolones (e.g. piquindone), i.e. two groups of drugs displaying the same D2 selectivity and Na+-dependent binding. We postulate that the close stereoelectronic similarity between zetidoline, orthopramides, and indolones accounts for their identical mechanism of action in the molecular level.

Chemical Phenomena↗
PubMed1988

Rapid group A streptococcal antigen detection kit: effect on antimicrobial therapy for acute pharyngitis.

Newly introduced rapid diagnostic tests for group A streptococcal pharyngitis should facilitate appropriate antimicrobial use in patients with group A streptococcal pharyngitis. Because of high rates of acute pharyngitis in Tuba City, AZ, at the Navajo Indian reservation, the use of rapid diagnostic test was prospectively evaluated. The sensitivity and specificity of the test was measured and changes in physician prescribing patterns attributable to use of the test were correlated. Of 320 patients with pharyngitis enrolled during the present 3-week study, 86 met the study's definition of a patient with streptococcal pharyngitis and 163 met the study's definition of a patient with nonstreptococcal pharyngitis. The rapid test was 62.8% sensitive and 96.9% specific in identifying patients from whom group A streptococci were isolated. Although treatment of patients with streptococcal pharyngitis at the time of the first visit increased from 36.5% in a retrospective sample to 72.5% during the study, treatment of patients in whom cultures were negative remained the same. Further analyses showed that physicians tended to treat patients with signs characteristic of streptococcal pharyngitis and, as the study progressed, to rely less on negative rapid test results as a reason to withhold antimicrobial agents. It was concluded that rapid tests with good specificity but limited sensitivity may improve treatment of patients with streptococcal pharyngitis by allowing earlier specific therapy. A more sensitive test with a higher negative predictive value would be necessary to prevent treatment of persons with nonstreptococcal pharyngitis.

Adolescent↗
PubMed1981

The soluble calcium-binding protein from muscle of the sandworm, Nereis virens.

Fast-acting muscle of the sandworm, Nereis virens, contains one soluble calcium-binding protein having a molecular weight close to 17 000 and occurring in the muscle at a concentration of approximately 0.1 mM. The protein binds two Ca2+ at equivalent sites with dissociation constant Kd = 6.4 X 10(-7) M. Its N-terminal amino acid is blocked by an N-acetyl group whereas glycine is the C-terminal residue. The comparison of the tryptic peptide map of this protein with those of the soluble calcium-binding protein from crayfish muscle, bovine brain calmodulin and rabbit skeletal muscle troponin C suggests that all of these proteins are homologous. Sandworm calcium-binding protein therefore belongs to the so-called cytosolic calcium EF-hand family. This protein is presumably the functional counterpart of vertebrate parvalbumin acting as soluble relaxing factor.

Amino Acids↗
PubMed1979

Parvalbumins from the lungfish (Protopterus dolloi).

Five parvalbumins have been isolated from the white muscles of the lungfish. They can be divided into two sub families showing typical amino acid compositions, C-terminal amino acid residues, peptide maps and immuno-reactivity. The red muscles including the cardiac muscle also contain parvalbumins in amounts roughly inversely related to the concentration of myoglobin in the muscle. Parvalbumins have also been detected in the brain and kidney.

Amino Acids↗