PubMed Health⌕ Search

Biomedical subjects

J Lehmann

Publications and source records attributed to J Lehmann.

At least 19 recordsLinked to original sources
PubMed1992

Strong competitive inhibition of porcine pancreatic alpha-amylase by aminodeoxy derivatives of maltose and maltotriose.

The syntheses are described of 6-amino-6-deoxymaltose (2), the 6-amino-6-deoxy (4), 6'-amino-6'-deoxy (6), and 6"-amino-6"-deoxy (8) derivatives of maltotriose, and the methyl alpha- (10) and beta-glycoside (12) and the 1-deoxy derivative (16) of 4. The Ki values (microM) of these competitive inhibitors of porcine pancreatic alpha-amylase were: 2, 88; 4, 1.9; 6, 2.0; 8, 175; 10, 360; 12, 9000; 16, 7600 (cf. 1800 for maltotriose and 3000 for methyl alpha-maltotrioside). The low values for 4 and 6 reflect reinforcement of the normal binding by ionic attraction and, possibly, interaction of the reducing end groups with the protein.

Amino Sugars↗
PubMed1992

Cortical norepinephrine release elicited in situ by N-methyl-D-aspartate (NMDA) receptor stimulation: a microdialysis study.

Norepinephrine (NE) release measured by microdialysis from probes positioned in the prefrontal cortex of anesthetized rats was increased when N-methyl-D-aspartate (NMDA) was contained in the microdialysis medium. NE release increased by a factor of 3.6 compared to prior baseline levels when 1 mM NMDA was applied for 30 min. This increase was largely reversible, and when a second stimulation was applied using aconitine (0.3 mM, 30 min), which acts on voltage-sensitive sodium channels, a second evoked release of NE was observed, of a similar magnitude as that evoked by NMDA. Dizocilpine (300 nM), which blocks cation channels associated with NMDA receptors, prevented the NMDA-elicited NE increase but not the aconitine-elicited increase.

Aconitine↗
PubMed1992

The selective protein kinase C inhibitor, NPC 15437, induces specific deficits in memory retention in mice.

We studied the effects of a selective inhibitor of protein kinase C (PKC), 2,6-diamino-N-[(1-(1-oxotridecyl)-2-piperidinyl]methyl)hexamide (NPC 15437), on acquisition and memory retention of a Y-maze avoidance task in mice. Post-training administration of NPC 15437 (0.1-10 mg/kg i.p.) induced a dose-dependent deficit in retention of the temporal but not the spatial component of the task. This selective amnesia does not reflect state dependence and NPC 15437 (1 mg/kg) had no effect on acquisition and memory retrieval. Our results suggest that this new PKC inhibitor interferes with mechanisms underlying memory consolidation. This is in agreement with recent findings suggesting that PKC is involved in memory processes.

Amnesia↗
PubMed1992

A spacer-modified disaccharide as a photoaffinity reagent for the acceptor-binding area of bovine (1----4)-beta-D-galactosyltransferase: comparison of its acceptor properties with those of other 2-acetamido-2-deoxy-beta-D-glucopyranosides.

The spacer-modified disaccharide 1,10-di-O-(2-acetamido-2-deoxy-beta-D-glucopyranosyl)-2-azi-1,10- decanediol (10) that mimics the biantennary core heptasaccharide of N-glycoproteins has been synthesised. Compound 10 is an excellent acceptor in galactosyltransferase-catalysed galactosylation by UDP-galactose, is superior (7-8-fold) to analogues that have only one GlcNAc unit, and is an efficient photoaffinity reagent for galactosyltransferase. In the presence of UDP-Gal, no photoaffinity labelling by 10 takes place, which agrees with the mechanism of galactosyltransferase action.

Animals↗
PubMed1992

Spacer-modified trisaccharide glycosides that mimic the biantennary Asn-linked oligosaccharide acceptor of (1----4)-beta-D-galactosyltransferase and can be used as competitive inhibitors and for irreversible deactivation.

The biantennary spacer-modified trisaccharide glycoside methyl 3,6-di-O-(2-acetamido-2-deoxy-beta-D-glucopyranosyloxyethyl)-alpha -D- mannopyranoside (5) was synthesised and used together with several 2-acylamino-2-deoxy-D-glucose derivatives in competition experiments with beta-D-galactosyltransferase. Compound 5 was an acceptor substrate (KM 0.18 mM) comparable to the biantennary core heptasaccharide of glycoproteins (KM 0.13 mM). Replacing the N-acetyl group by other N-acyl groups did not alter the kinetic parameters significantly. When the N-acyl group was iodoacetyl, the compound was an irreversible inhibitor.

Asparagine↗
PubMed1992

Homodimer formation of retinoid X receptor induced by 9-cis retinoic acid.

Retinoid response pathways are mediated by two classes of receptors, the retinoic acid receptors (RARs) and the retinoid X receptors (RXRs). A central question is whether distinct response pathways are regulated by these two classes of receptors. The observation that the stereoisomer 9-cis-retinoic acid binds with high affinity to RXRs suggested that this retinoid has a distinct role in controlling RXR activity, but it was almost simultaneously discovered that RXRs function as auxiliary receptors for RARs and related receptors, and are essential for DNA binding and function of those receptors. Hence, although RARs seem to operate effectively only as heterodimeric RAR/RXR complexes, RXRs themselves apparently function predominantly, if not exclusively, as auxiliary receptors. Here we report that 9-cis-retinoic acid induces RXR homodimer formation. Our results demonstrate a new mechanism for retinoid action by which a ligand-induced homodimer mediates a distinct retinoid response pathway.

Animals↗
PubMed1992

Investigation of the active site of Escherichia coli beta-D-galactosidase by photoaffinity labelling.

3,7-Anhydro-2-azi-1,2-dideoxy-D-glycero-L-manno-(8-3H)octitol++ + (1a) and 3-azibutyl 1-thio-beta-D-(6-3H)galactopyranoside (2a) were synthesised from the unlabelled compounds by reaction with galactose oxidase, then reduction with sodium borotritide. Whereas 1a was an efficient photoaffinity reagent for the beta-D-galactosidase from E. coli, 2a was ineffective. Three 3H-labelled peptides were isolated after digestion of the labelled enzyme with trypsin, one of which was an octapeptide (Trp 158 to Ser 165), which is remote from the segments detected as part of the active site of the enzyme.

Affinity Labels↗
PubMed1992

Studies of the interaction of the maltose-binding protein of Escherichia coli, a closed-groove binder, with 4,6-O-ethylidenemalto-oligosaccharides (dp 2-5) and its regioselective labelling with 3-azibutyl 1-thio-alpha-(6-3H)maltoside.

Four malto-oligosaccharides (dp 2-5), each with a 4,6-O-ethylidene group on the glucosyl unit at the non-reducing terminus, were synthesised and used to prove that the maltose-binding protein (MBP) of E. coli is a closed-groove binder. alpha-D-Glucosylation of 3-azibutyl 1-thio-alpha-D-(6-3H)glucopyranoside yielded a 3H-labelled, photolabile 1-thiomaltoside derivative that was used to chemically modify the binding site of MBP. The 3H-labelled peptide containing 83% of the total radioactivity, which was isolated after tryptic cleavage of the modified MBP and sequenced, is part of the closed end of the MBP groove.

ATP-Binding Cassette Transporters↗
PubMed1992

Spacer-modified saccharides for the regioselective photoaffinity labelling of the binding site of an immunoglobulin.

The spacer-modified trisaccharides that mimic (1----6)-linked beta-D-galactotetraose (Gal4), namely, O-beta-D-galactopyranosyl-(1----6)-S-beta-D-galactopyranosyl-(1----11)-8 -azi- 6,7,8,9,10-pentadeoxy-11-thio-D-galacto-undecose (12) and O-beta-D-galactopyranosyl-(1----6)-O-beta-D-galactopyranosyl- (1----13)-8-azi-6,7,8,9,10,11,12-heptadeoxy-D-galacto-tri decose (20) were synthesised by coupling disaccharide derivatives with 8-azi-6,7,8,9,10-pentadeoxy-1,2:3,4-di-O-isopropylidene-11-O -tosyl-alpha-D-galacto-undecopyranose (10) and 8-azi-6,7,8,9,10,11,12-heptadeoxy-1,2:3,4-di-O-isopropyli den e-alpha-D-galacto- tridecopyranose (17), respectively. Compounds 12 and 20 had affinities for the combining sites of the antibodies IgA X24 and IgA J 539 similar to those of O-beta-D-galactopyranosyl-(1----6)-O-beta-D- galactopyranosyl-(1----11)-8-azi-6,7,8,9,10-pentadeoxy-D-gal acto-undecose (7) and the native ligand Gal4. Tritium-labelled 7 chemically modified the heavy and light chains of IgA J 539, whereas 8-azi-6,7,8,9,10-pentadeoxy-D-(11-3H)galacto-undecose (5a) reacted only with the heavy chain.

Affinity Labels↗
PubMed1992

Spacer-modified, photolabile tetrasaccharides as analogues of maltopentaose are versatile probes for porcine pancreatic alpha-amylase.

The syntheses are described of methyl 4'-O-[4-S-(3-azi-4-alpha-D-glucopyranosyloxybutyl)-6-deoxy-4 -thio-alpha-D-xylo-hex-5-enopyranosyl]-alpha-maltoside (28), methyl 4-O-[4-S-(3-azi-4-alpha-maltosyloxybutyl)-6-deoxy-4-thio- alpha-D-xylo-hex-5-enopyranosyl]-alpha-D-glucopyranoside (29), and methyl 4-S-(3-azi-4-alpha-maltotriosyloxybutyl)-6-deoxy-4-thio- alpha-D-xylo-hex-5-enopyranoside (30), which are analogues of maltopentaose in which a central glucosyl unit is replaced by an acyclic, four-membered hydrocarbon spacer carrying a photolabile azi group. Only 30 was slowly cleaved by high concentrations of pancreatic alpha-amylase. The Ki values (mM) were 0.15 (28), 2.1 (29), and 2.5 (30). Deactivation of the enzyme by irradiation in the presence severely of 28-30 was 96.4%, 98.1%, and 40%, respectively. There is an indication for regiospecific photoaffinity labelling of the binding subsites of the enzyme.

Affinity Labels↗
PubMed1992

The autoinhibitory feedback control of acetylcholine release in human neocortex tissue.

Slices of human neocortex prelabelled with [3H]choline were superfused and stimulated electrically (3 Hz, 2 ms, 24 mA) in order to investigate the autoreceptor-mediated modulation of acetylcholine (ACh) release. The concentration-response curve of the muscarinic agonist oxotremorine (pKd = 6.76 +/- 0.06), which was equipotent to ACh, was shifted to the right in a parallel manner by atropine (pA2 = 8.56 +/- 0.11), as evaluated by non-linear regression analysis. Calculation of the biophase concentration of ACh showed that no ACh could be assumed to be present under these conditions, whereas following inhibition of the acetylcholinesterase by physostigmine (0.1 microM) a biophase concentration of 10(-6.89 +/- 0.11) M was estimated. The depression of ACh release due to physostigmine and tacrine, another anticholinesterase, was antagonized by atropine. When the autoinhibition was operative atropine and the M2 subtype specific muscarinic antagonists, AF-DX 116 and methoctramine, significantly increased the release of ACh whereas the 'facilitatory' effects of the M1 and M3-specific drugs, pirenzepine and hexahydrosiladifenidol, were not significant. Although different disinhibitory effects of the subtype-specific antagonists were found, they did, however, not show a pattern which would allow a clear characterisation of the subtype of muscarinic receptor associated with the autoreceptor. The release of ACh from neocortex tissue of the (non-demented) neurosurgical patients decreased with their age. This finding is consistent with the hypothesis that the normal aging process resembles a delayed and attenuated disease process of senile dementia of Alzheimer's type.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗
PubMed1992

Spacer-modified disaccharide and pseudo-trisaccharide methyl glycosides that mimic maltotriose, as competitive inhibitors for pancreatic alpha-amylase: a demonstration of the "clustering effect".

The synthesis is reported of methyl 4,4'-dithio-alpha-maltotrioside (12) and the spacer-modified disaccharide glycosides methyl 4-S-(4-alpha-D-glucopyranosylthio-2-hydroxybutyl)-4-thio-alpha -D-glucopyranoside (20) and methyl 4-S-[(1,5/4,6)- and (4,6/1,5)-4-alpha-D-glucopyranosylthio-5,6-dihydroxy-2- cyclohexen-1-yl]-4-thio-alpha-D-glucopyranoside (29a/b), which are analogues of methyl alpha-maltotrioside. The Ki values for alpha-amylase for these compounds were determined as were those of methyl alpha-maltotrioside and maltose.

Carbohydrate Sequence↗
PubMed1992

Stereochemistry of D-galactal and D-galacto-octenitol hydration by coffee bean alpha-galactosidase: insight into catalytic functioning of the enzyme.

Green coffee bean alpha-galactosidase was found to catalyze the hydration of D-galactal and (Z)-3,7-anhydro-1,2-dideoxy-D-galacto-oct-2-enitol (D-galacto-octenitol), each a known substrate for beta-galactosidase. The hydration of D-galactal by the alpha-galactosidase in D2O yielded 2-deoxy-2(S)-D-[2-2H]galactose; the hydration of D-[2-2H]galacto-octenitol in H2O yielded 1,2-dideoxy-2(R)-D-[2-2H]galactooct-3-ulose. Thus, the enzyme protonated each substrate from beneath the plane of the ring, as assumed for alpha-D-galactosides. These results provide an unequivocal assignment of the orientation of an acidic catalytic group to the alpha-galactosidase reaction center. In addition, they reveal a pattern of glycal/exocyclic enitol/glycoside protonation by the enzyme that differs from the pattern reported for beta-galactosidase and from that reported for alpha-glucosidases. Further findings show that D-galacto-octenitol is hydrated by the coffee bean alpha-galactosidase to form the alpha-anomer of 1,2-dideoxy-D-galactooctulose and by Escherichia coli beta-galactosidase to form the beta-anomer. That each enzyme converts this enolic substrate to a product whose de novo anomeric configuration matches that formed from its D-galactosidic substrates provides new evidence for the role of protein structure in controlling the steric outcome of reactions catalyzed by these and other glycosylases. The findings are discussed in light of the concept that catalysis by glycosidases involves a "plastic" protonation phase and a "conserved" product configuration phase.

Carbohydrate Conformation↗
PubMed1992

Optimal medium use for continuous high density perfusion processes.

For maintenance of high cell density in continuous perfusion processes not only feeding with substrates but also removal of inhibitors and toxic waste products are of special interest. High perfusion rates cause large volumes of product containing medium which have to be processed in product isolation. In order to minimize these volumes concentrated feed solutions of optimized medium are used. On the other hand, such media may cause high concentrations of toxic or inhibitory metabolites which can negatively influence cell growth and product formation. Especially, if the spent medium (or special parts of it) is used again after product isolation, the removal or even better the control of inhibitor production is of highest importance. We have developed a continuous fermentation concept and system (continuous medium cycle bioreactor, cMCB) in which both limitation and inhibition effects can be generated to identify special substances as limiting or inhibitory components. With the results from those experiments it was possible to lower the total perfusion rate during serum-free perfusion cultures of hybridoma cells and to obtain an optimal substrate utilization. The advantages for decreasing the production costs (for media, special supplements and product isolation) are obvious. The other aim of this study was to identify secreted metabolic waste products as inhibitor or toxic metabolite.

Animals↗
PubMed1992

Photolabile derivatives of maltose and maltotriose as ligands for the affinity labelling of the maltodextrin-binding site in porcine pancreatic alpha-amylase.

The 3-azibutyl group was linked through sulfur to the anomeric position of maltose and maltotriose to yield the photolabile thioglycosides 3-azibutyl 1-thio-alpha-maltoside (11) and 3-azibutyl 1-thio-alpha-maltotrioside (12), and to the 4'- and 6'-position of maltose to give the thioethers 4'-S-(3-azibutyl)-4'-thiomaltose (8) and 6'-S-(3-azibutyl)-6'-thiomaltose (15). All four compounds were good competitive inhibitors of the action of porcine pancreatic alpha-amylase. Compound 12 irreversibly deactivated the enzyme to approximately 100% when irradiated together with the protein. The other compounds were much less effective. It is likely that separate areas of the enzyme binding site are chemically modified by the different ligands.

Affinity Labels↗
PubMed1992

Differences in mental task performance and slow potential shifts in subjects differing in cortisol level.

Hormones of the pituitary-adrenocortical axis (e.g., cortisol) are involved in the regulation of brain function. This study was aimed to clarify whether individual differences in baselines of cortisol are related to differences in heart rate (HR), slow brain potential shifts (SPS), performance data and personality. 17 males were instructed to solve 120 arithmetical tasks under time stress conditions. They could obtain monetary bonuses according to the accuracy of their task performance. This test condition was compared to a control condition. To determine the plasma level of cortisol by radioimmunoassays four blood samples were collected during the session. Baselines were estimated twice. A clustering procedure with respect to all cortisol levels resulted in a group of high responders (HC, n = 9) and a group of low responders (LC, n = 8). The HR was significantly higher in the HC group. The SPS of the LC group were characterized by a larger P300 elicited by the task followed by a steep negative slow wave (NSW) as compared to the HC group. LC subjects also showed a higher NSW before feedback presentation. The LC group solved the tasks faster and obtained more than twice the reward than the other group. They scored higher in achievement motivation and also reported increased 'Social Acceptance' and decreased 'Tiredness'. In sum, the results suggest a more efficient regulation of the arousal level of the LC group in contrast to the HC group as far as reflected in the parameters analysed.

Adolescent↗