Biomedical subjects

P Schreier

Publications and source records attributed to P Schreier.

At least 19 recordsLinked to original sources

PubMed2005

Calcium tartrate crystals in the midgut of the grape leafhopper.

Calcium tartrate crystals were observed in the midgut of grape leafhoppers. This unique compound was found for the first time in insects. The size of the crystals varied strongly between and within individuals with a mean length of 153 +/- 87 microm and a mean width of 71 +/- 46 microm. In addition, the number of crystals per individual showed a broad variation and ranged from 1 to 150 crystals/individual. The occurrence of calcium tartrate crystals as well as the number of crystals per individual followed the same seasonal pattern as seasonal vine leaf concentrations of tartaric acid found in a previous study, indicating that calcium tartrate is formed to neutralize the tartaric acid in the gut system. It further implies that the grape leafhopper, rather than being a pure phloem sucker, employs a mixed feeding strategy to satisfy its demands for calcium uptake.

Animals↗

PubMed2004

Occurrence of 2-ethylhexanoic acid in foods packed in glass jars.

After simultaneous distillation-extraction (SDE) of commercial baby foods (n = 20) and fruit juices (n = 15) (among them 15 and eight products labelled 'organic', respectively) from 11 different suppliers, analyses performed by coupled capillary gas chromatography-mass spectrometry (GC-MS) revealed the presence of 2-ethylhexanoic acid (2-EHA), a known teratogenic compound. 2-EHA was found in 80 and 73% of the baby foods and fruit juices, respectively. Amounts ranged from 0.25 to 3.2 mg kg(-1)(average, 0.55 mg kg(-1)) and from 0.01 to 0.59 mg l(-1) (average, 0.18 mg l(-1)) in baby foods and fruit juices, respectively. GC-MS analysis of the SDE extracts obtained from the plastic gaskets inside the metal lids of the samples under study revealed the gaskets to be the origin of 2-EHA. As shown from the non-contaminated samples under study, obviously technology is available to avoid 2-EHA contamination of glass jar-packed food.

Beverages↗

PubMed2001

A new one-step strategy for the stereochemical assignment of acyclic 2- and 3-sulfanyl-1-alkanols using the CD exciton chirality method.

A new one-step strategy is described for the stereochemical assignment of acyclic 2- and 3-sulfanyl-1-alkanols using the CD exciton chirality method. Using the 9-anthroate chromophore for the derivatization of both functional groups, the resulting bisignate CD curves unequivocally allow the determination of the stereochemistry from a single CD measurement. The usefulness of the new method is demonstrated using synthesized optically pure 3-sulfanyl-1-hexanols and 2-sulfanyl-1-hexanols as model compounds. The developed microscale method is also useful for the stereochemical assignment of 1,2- and 1,3-diols. To our knowledge this is the first application of the CD exciton chirality method to acyclic 2- and 3-sulfanyl-1-alkanols.

Journal Article↗

PubMed2001

Beta-glucosidase multiplicity from Aspergillus tubingensis CBS 643.92: purification and characterization of four beta-glucosidases and their differentiation with respect to substrate specificity, glucose inhibition and acid tolerance.

From Aspergillus tubingensis CBS 643.92 four distinct beta-glucosidases (I-IV) were purified by a four-step purification procedure. SDS-PAGE revealed molecular masses of 131, 126, 54 and 54 kDa, respectively, and their isoelectric points were determined to be 4.2, 3.9, 3.7 and 3.6, respectively. The beta-glucosidases exhibited high diversity with respect to pH and temperature optima and stability, as well as to substrate specificity and glucose tolerance. The major beta-glucosidase (I) preferentially hydrolysed oligosaccharides. The acid-stable and heat-tolerant beta-glucosidase II hydrolysed aryl and terpenyl beta-D-glucosides as well as 1-O-trans-cinnamoyl beta-D-glucoside. In contrast to beta-glucosidases I and II, the minor beta-glucosidases III and IV were found to be glucose-tolerant; inhibition constants of 470 and 600 mM, respectively, were determined.

Amino Acid Sequence↗

PubMed2001

Naturally occurring benzodiazepines may codetermine chronotypes.

Determinants of individual differences in sleep-wake cycles and vigilance are being recognized as major factors of influence in both physical and mental health. Alterations of an accustomed circadian sleep-wake rhythm are commonly seen in the early stages of the majority of psychiatric disorders and, by themselves, predispose to significant morbidity even in the absence of an underlying illness. While it is well known that disruptions of sleep respond favourably to benzodiazepines, agents which have been prescribed for insomnia since their industrial synthesis in the early 1960s, little attention has been paid to putative central nervous system effects of naturally occurring benzodiazepines. These molecules were found in various nutritive plants and have been quantified in human brain and peripheral blood of drug-naive individuals at trace amounts. There is agreement that elevated concentrations of naturally occurring benzodiazepines participate in the complex pathophysiology of hepatic encephalopathy, a condition asssociated with progressive impairment of consciousness and, ultimately, coma. In the present study, we address the relationship between naturally occurring benzodiazepines and time-of-day effects on the behavior of healthy subjects.

Adult↗

PubMed2001

Quercetin 3,3',4'-tri-O-beta-D-glucopyranosides from leaves of Eruca sativa (Mill.).

Three new quercetin 3,3',4'-tri-O-beta-D-glucopyranosides isolated from leaves of Eruca sativa (Mill.) were identified as quercetin 3,3',4'-tri-O-beta-D-glucopyranoside, quercetin 3'-(6-sinapoyl-O-beta-D-glucopyranosyl)-3,4'-di-O-beta-D-glucopyranoside and quercetin 3-(2-sinapoyl-O-beta-D-glucopyranosyl)-3'-(6-sinapoyl-O-beta-D-glucopyranosyl)-4'-O-beta-D-glucopyranoside. The structures were established by one- and two-dimensional 1H and 13C NMR spectra as well as b

Brassicaceae↗

PubMed2001

Flavor authenticity studies by (2)h/(1)h ratio determination using on-line gas chromatography pyrolysis isotope ratio mass spectrometry.

Based on (2)H/(1)H ratio measurements of commercial synthetic and "natural" references, the recently developed on-line gas chromatography pyrolysis isotope ratio mass spectrometry (HRGC-P-IRMS) technique was used to determine the delta(2)H(SMOW) values of the flavor compounds decanal, linalool, and linalyl acetate, as well as those of E-2-hexenal and E-2-hexenol in foods and essential oils. In preceding model studies, the influence of sample preparation steps (simultaneous distillation extraction, SDE; solvent extraction, SE; liquid liquid extraction, LLE) on the delta(2)H values was found to be negligible. For decanal, the typical (2)H abundance, with higher content of (2)H for synthetic material (delta(2)H(SMOW) from -90 to -156 per thousand) and lower (2)H content for natural references (delta(2)H(SMOW) from -138 to -262 per thousand) was observed. Although the delta(2)H data recorded for linalool did not allow one to distinguish between synthetic (delta(2)H(SMOW) from -207 to -301 per thousand) and natural (delta(2)H(SMOW) from -234 to -333 per thousand) materials, the situation was somewhat more encouraging for linalyl acetate; delta(2)H(SMOW) values from -199 to -239 per thousand and from -213 to -333 per thousand were found for synthetic and natural samples, respectively. E-2-Hexenal and E-2-hexenol showed clear-cut origin-dependent differences in their (2)H/(1)H ratios; that is, delta(2)H(SMOW) values from -14 to -109 per thousand and from -263 to -415 per thousand as well as from -41 to -131 per thousand and from -238 to -348 per thousand were recorded for products from synthetic and natural origins, respectively.

Acyclic Monoterpenes↗

PubMed2000

Pharmacological profile of apigenin, a flavonoid isolated from Matricaria chamomilla.

Dried flowers of Matricaria chamomilla L. are largely used to provide sedative as well as spasmolytic effects. In the present study, we examined in particular the pharmacological property of a fraction isolated from a methanolic extract of M. chamomilla, which was identified by HPLC-MS-MS analysis as apigenin. By radioreceptor binding assays, we demonstrated the ability of the flavone to displace a specific radioligand, [(3)H]Ro 15-1788, from the central benzodiazepine binding site. Electrophysiological studies performed on cultured cerebellar granule cells showed that apigenin reduced GABA (gamma-aminobutyric acid)-activated Cl(-) currents in a dose-dependent fashion. The effect was blocked by co-application of Ro 15-1788, a specific benzodiazepine receptor antagonist. Accordingly, apigenin reduced the latency in the onset of picrotoxin-induced convulsions. Moreover, apigenin injected i.p. in rats reduced locomotor activity, but did not demonstrate anxiolytic, myorelaxant, or anticonvulsant activities. The present results seem to suggest that the inhibitory activity of apigenin on locomotor behaviour in rats cannot be ascribed to an interaction with GABA(A)-benzodiazepine receptor but to other neurotransmission systems, since it is not blocked by Ro 15-1788.

Animals↗

PubMed2000

Identification of benzodiazepines in Artemisia dracunculus and Solanum tuberosum rationalizing their endogenous formation in plant tissue.

Sterile cultivated plant cell tissues and cell regenerates of several species were tested for their binding affinity to the central human benzodiazepine receptor. Binding activity was found in extracts of Artemisia dracunculus cell tissue (IC(50) = 7 microg/ml) and, to a lesser extent, in plant regenerates of potato herb (Solanum tuberosum). Preparative HPLC led to the isolation of fractions with a significant displacing potency in the benzodiazepine receptor binding assay. Using on-line HPLC-electrospray-tandem mass spectrometry (HPLC-ESI-MS/MS) in the "selected reaction monitoring" (SRM) mode, delorazepam and temazepam were found in amounts of about 100 to 200 ng/g cell tissue of Artemisia dracunculus, whereas sterile potato herb contained temazepam and diazepam ranging approximately from 70 to 450 ng/g cell tissue. It is the first report on the endogenous formation of benzodiazepines by plant cells, as any interaction of microorganisms and environmental factors was excluded.

Artemisia↗

PubMed2000

Biocatalytic asymmetric hydroxylation of hydrocarbons with the topsoil-microorganism Bacillus megaterium.

A Bacillus megaterium strain was isolated from topsoil by a selective screening procedure with allylbenzene as a xenobiotic substrate. This strain performed the hydroxylation chemoselectively (no arene oxidation and overoxidized products) and enantioselectively (up to 99% ee) in the benzylic and nonbenzylic positions of a variety of unfunctionalized arylalkanes. Salycilate and phenobarbital, which are potent inducers of cytochrome P-450 activity, changed the regioselectivity of the microbial CH insertion, without an effect on the enantioselectivity. The biotransformation conditions were optimized in regard to product yield and enantioselectivity by variation of the oxygen-gas supply and the time of the substrate addition. The different product distributions (alpha- versus beta-hydroxylated product) that are obtained on induction of cytochrome P-450 enzyme activity demonstrate the involvement of two or more hydroxylating enzymes with distinct regioselectivities in this biotransformation. An oxygen-rebound mechanism is assumed for the cytochrome P-450-type monooxygenase activity, in which steric interactions between the substrate and the enzyme determine the preferred face of the hydroxy-group transfer to the radical intermediate.

Bacillus megaterium↗

PubMed2000

Microscale determination of the absolute configuration of alpha-aryl-substituted alcohols by the CD exciton chirality method

The absolute configurations of a broad spectrum of aryl alcohols 1 have been determined for the first time by the CD exciton chirality method. The configurational assignment is additionally verified by computer modeling and lipase-catalyzed acetylation of the racemic alcohols. The CD-spectroscopic data have revealed that the S enantiomers of the benzoate derivatives 2 display a positive first Cotton effect and the R enantiomers a negative one at around 228 nm. Thus, the sense of the first Cotton effect of the benzoate derivative 2 allows a reliable assignment of the absolute configuration of the corresponding alcohol 1.

Journal Article↗

PubMed2000

Naturally occurring benzodiazepines: current status of research and clinical implications.

Naturally occurring benzodiazepines (BZDs) were first detected in mammalian tissues in 1986. They comprise a variety of 1,4-benzodiazepines corresponding to drugs commercially available for the treatment of anxiety disorders, sleep disturbances and epileptic seizures. Several biosynthetic pathways leading to the formation of BZDs are currently being discussed and have led to the proposition of possible precursor molecules. For years, the identification of naturally occurring BZDs in mammalian organisms was mostly confined to post mortem CNS material for sensitivity reasons. While radioimmunoassay and radioreceptor assay techniques have been tentatively applied to quantitations of genuine BZDs from human milk and cerebrospinal fluid, accurate measurements in peripheral blood have only recently become accessible, e. g., by gas chromatography/selected ion monitoring-mass spectrometry (GC/SIM-MS). This review summarizes existing evidence of benzodiazepines' occurrence in nature and discusses implications for neuropsychiatric disorders.

Animals↗

PubMed2000

beta-glucosidases from five black Aspergillus species: study of their physico-chemical and biocatalytic properties.

Five black Aspergillus strains (A. aculeatus, A. foetidus, A. japonicus, A. niger, and A. tubingensis) were cultivated on crude wheat arabinoxylan as the carbon source under defined pH, temperature, and oxygen conditions. Protein and beta-glucosidase content differed remarkably within the obtained culture filtrates, of which eleven beta-glucosidases were isolated. Seven beta-glucosidases were purified to apparent electrophoretic homogeneity using anion-exchange and gel-permeation chromatography. They were found to be acidic proteins and most of them appeared to be glycoproteins with a molecular mass between 93 and 142 kDa. Classification of the beta-glucosidases into four groups (I-A, I-B, II, and III) is suggested according to their physicochemical and biocatalytic properties. The major beta-glucosidases were assigned to groups I-A and I-B, the minor beta-glucosidases to groups II and III, comprising acid-tolerant and glucose-tolerant enzymes, respectively.

Amino Acid Sequence↗

PubMed2000

A dual function alpha-dioxygenase-peroxidase and NAD(+) oxidoreductase active enzyme from germinating pea rationalizing alpha-oxidation of fatty acids in plants.

An enzyme with fatty acid alpha-oxidation activity (49 nkat mg(-1); substrate: lauric acid) was purified from germinating pea (Pisum sativum) by a five-step procedure to apparent homogeneity. The purified protein was found to be a 230-kD oligomer with two dominant subunits, i.e. a 50-kD subunit with NAD(+) oxidoreductase activity and a 70-kD subunit, homolog to a pathogen-induced oxygenase, which in turn shows significant homology to animal cyclooxygenase. On-line liquid chromatography-electrospray ionization-tandem mass spectrometry revealed rapid alpha-oxidation of palmitic acid incubated at 0 degrees C with the purified alpha-oxidation enzyme, leading to (R)-2-hydroperoxypalmitic acid as the major product together with (R)-2-hydroxypalmitic acid, 1-pentadecanal, and pentadecanoic acid. Inherent peroxidase activity of the 70-kD fraction decreased the amount of the (R)-2-hydroperoxy product rapidly and increased the level of (R)-2-hydroxypalmitic acid. Incubations at room temperature accelerated the decline toward the chain-shortened aldehyde. With the identification of the dual function alpha-dioxygenase-peroxidase (70-kD unit) and the related NAD(+) oxidoreductase (50-kD unit) we provided novel data to rationalize all steps of the classical scheme of alpha-oxidation in plants.

Amino Acid Sequence↗

PubMed1999

Biotransformation of (1-phenyl)ethyl hydroperoxide with Aspergillus niger: a model study on enzyme selectivity and on the induction of peroxidase activity.

The biocatalytic enantioselective reduction of (1-phenyl)ethyl hydroperoxide (1) by the fungus Aspergillus niger to the corresponding alcohol 2 involves a multi-enzyme biotransformation of the hydroperoxide 1, as revealed by the change in the enantioselectivity as a function of incubation times. This unusual behavior is not exhibited by other fungi and seems to be restricted to A. niger. Furthermore, the peroxidase and other oxidoreductase activities of A. niger depend on the availability of metal ions such as Fe2+, Mn2+ and Zn2+ in the growth medium, since the addition of Fe2+ ions substantially (threefold) increases the enantioselectivity, whereas addition of Mn2+ and Zn2+ ions decreases it. Finally, the cold shock (4 degrees C) significantly enhances the reduction of the hydroperoxide by the microorganism A. niger.

Aspergillus niger↗

PubMed1999

Biotransformations with peroxidases.

Enzymes are chiral catalysts and are able to produce optically active molecules from prochiral or racemic substrates by catalytic asymmetric induction. One of the major challenges in organic synthesis is the development of environmentally acceptable chemical processes for the preparation of enantiomerically pure compounds, which are of increasing importance as pharmaceuticals and agrochemicals. Enzymes meet this challenge! For example, a variety of peroxidases effectively catalyze numerous selective oxidations of electron-rich substrates, which include the hydroxylation of arenes, the oxyfunctionalizations of phenols and aromatic amines, the epoxidation and halogenation of olefins, the oxygenation of heteroatoms and the enantioselective reduction of racemic hydroperoxides. In this review, we summarize the important advances achieved in the last few years on peroxidase-catalyzed transformations, with major emphasis on preparative applications.

Biotransformation↗

PubMed1999

Chemical engineering of enzymes: altered catalytic activity, predictable selectivity and exceptional stability of the semisynthetic peroxidase seleno-subtilisin.

The increasing demand for enzymes as highly selective, mild, and environmentally benign catalysts is often limited by the lack of an enzyme with the desired catalytic activity or substrate selectivity and by their instability in biotechnological processes. The previous answers to these problems comprised genetically engineered enzymes and several classes of enzyme mimics. Here we describe the potential of chemical enzyme engineering: native enzymes can be modified by merely chemical means and basic equipment yielding so-called semisynthetic enzymes. Thus, the high substrate selectivity of the enzymatic peptide framework is combined with the catalytic versatility of a synthetic active site. We illustrate the potential of chemically engineered enzymes with the conception of the semisynthetic peroxidase seleno-subtilisin. First, the serine endoprotease subtilisin was crystallized and cross-linked with glutaraldehyde to give cross-linked enzyme crystals which were found to be insoluble in water or organic solvents and highly stable. Second, serine 221 in the active site (Enz-OH) was chemically converted into an oxidized derivative of selenocystein (Enz-SeO2H). As a consequence, the former proteolytic enzyme gained peroxidase activity and catalyzed the selective reduction of hydroperoxides. Due to the identical binding sites of the semisynthetic peroxidase and the protease, the substrate selectivity of seleno-subtilisin was predictable in view of the well-known selectivity of subtilisin.

Binding Sites↗

PubMed1999

Occurrence of emodin, chrysophanol and physcion in vegetables, herbs and liquors. Genotoxicity and anti-genotoxicity of the anthraquinones and of the whole plants.

1,8-Dihydroxyanthraquinones, present in laxatives, fungi imperfecti, Chinese herbs and possibly vegetables, are in debate as human carcinogens. We screened a variety of vegetables (cabbage lettuce, beans, peas), some herbs and herbal-flavoured liquors for their content of the 'free' anthraquinones emodin, chrysophanol and physcion. For qualitative and quantitative analysis, reversed-phase HPLC (RP-LC), gas chromatography-mass spectrometry (GC-MS) and RP-LC-MS were used. The vegetables showed a large batch-to-batch variability, from 0.04 to 3.6, 5.9 and 36 mg total anthraquinone per kg fresh weight in peas, cabbage lettuce, and beans, respectively. Physcion predominated in all vegetables. In the herbs grape vine leaves, couch grass root and plantain herb, anthraquinones were above the limit of detection. Contents ranged below 1 mg/kg (dry weight). All three anthraquinones were also found in seven of 11 herbal-flavoured liquors, in a range of 0.05 mg/kg to 7.6 mg/kg. The genotoxicity of the analysed anthraquinones was investigated in the comet assay, the micronucleus test and the mutation assay in mouse lymphoma L5178Y tk+/- cells. Emodin was genotoxic, whereas chrysophanol and physcion showed no effects. Complete vegetable extract on its own did not show any effect in the micronucleus test. A lettuce extract completely abolished the induction of micronuclei by the genotoxic anthraquinone danthron. Taking into consideration the measured concentrations of anthraquinones, estimated daily intakes, the genotoxic potency, as well as protective effects of the food matrix, the analysed constituents do not represent a high priority genotoxic risk in a balanced human diet.

Animals↗