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Biomedical subjects

K Bock

Publications and source records attributed to K Bock.

At least 91 records · Page 5Linked to original sources
PubMed1992

Regulation of androgen receptor mRNA and protein level by steroid hormones in human mammary cancer cells.

The regulation of the human androgen receptor (AR) by steroid hormones in human mammary cancer cells was investigated using immunocytochemical and ligand binding assays for its protein and Northern blot analyses for the corresponding mRNA. MFM-223 cells contain high levels of ARs and are growth-inhibited by dihydrotestosterone (DHT). The AR protein is down-regulated to 57% of the control by 10 nM DHT after 24 h, and the corresponding mRNA is also reduced. The nonsteroidal antiandrogen hydroxyflutamide had no effect on the AR level, whereas after incubation with 1 microM cyproterone acetate a slight down-regulation was observed. The AR level was restored completely after release from a 7 day treatment with DHT. However, only 60% of the control level was restored, if the cells wer grown in the presence of DHT for 6 weeks. In androgen-pretreated cells the proliferation rate remained decreased even after the withdrawal of DHT. Concomitantly the distinct growth inhibition was lost. Transfection experiments demonstrated a reduced activity of the residual androgen receptor in these pretreated cells. In addition to the AR, EFM-19 cells also contain significant amounts of estrogen and progesterone receptors. EFM-19 cells are not growth inhibited by physiological concentrations of DHT. Autoregulation of AR was also found in this cell line. Additionally, reduced levels of AR protein and mRNA were found in EFM-19 cells after treatment with the synthetic progestin R5020. The maximum effect of R5020 was observed at the high concentration of 1 microM. Estrogen treatment with 10 nM 17 beta-estradiol for 3 days reduced the AR level only by 25%.

Blotting, Northern↗
PubMed1992

From conceptual roles to structural relations: bridging the syntactic cleft.

The distinction between underlying and superficial linguistic structure is a staple of modern cognitive psychology. Despite increasingly diverse conceptions of syntactic relations in linguistic theory, the received view in psycholinguistics has remained one in which the entities assigned to underlying relations may assume different surface relations. The present article examines this view in the context of language production and reviews evidence that the disposition to bind animate entities to the surface subject relation is a basic feature of language use, suggesting that mappings from conceptual categories to syntactic relations form a main support of the bridge from conception to language. Proceeding on this assumption, the article also evaluates competing accounts of the mapping process in production. The results argue against syntactic relation-changing operations, but favor a division between meaning- and form-related mechanisms.

Concept Formation↗
PubMed1992

The tip-of-the-tongue phenomenon: blocking or partial activation?

Tip-of-the-tongue states may represent the momentary unavailability of an otherwise accessible word or the weak activation of an otherwise inaccessible word. In three experiments designed to address these alternative views, subjects attempted to retrieve rare target words from their definitions. The definitions were followed by cues that were related to the targets in sound, by cues that were related in meaning, and by cues that were not related to the targets. Experiment 1 found that compared with unrelated cues, related cue words that were presented immediately after target definitions helped rather than hindered lexical retrieval, and that sound cues were more effective retrieval aids than meaning cues. Experiment 2 replicated these results when cues were presented after an initial target-retrieval attempt. These findings reverse a previous one (Jones, 1989) that was reproduced in Experiment 3 and shown to stem from a small group of unusually difficult target definitions.

Adult↗
PubMed1992

Synthesis of deoxy derivatives of lactose and their hydrolysis by beta-galactosidase from E. coli.

Methyl 2-deoxy-alpha-lactoside, methyl 3-deoxy-beta-lactoside, 1,5-anhydro-4-O-beta-D-galactopyranosyl-D-glucitol and the 2-deoxy and 2,3-dideoxy derivatives of 1,5-anhydro-4-O-beta-D-galactopyranosyl-D-glucitol have been synthesized by deoxygenation of lactose derivatives at appropriate positions. Cyclohexyl beta-D-galactopyranoside has also been synthesized. All derivatives proved to be substrates for the enzyme beta-galactosidase from E. coli, but the rate of hydrolysis of the substrate analogues was strongly dependent on the nature of the aglycone.

Carbohydrate Sequence↗
PubMed1992

The function of the 5-hydroxymethyl group of lactose in enzymatic hydrolysis with beta-galactosidase from E. coli.

A series of 6-substituted methyl lactoside derivatives together with methyl allolactoside and (6S)-methyl [6-2H]lactoside have been synthesized and characterized by NMR spectroscopy. All compounds were tested as substrates for the enzyme beta-galactosidase from E. coli using progress curve kinetic methology both in single-substrate and competition experiments. The results show that the hydrolysis of methyl lactoside to a large extent takes place through an intramolecular transglycosidation reaction via allolactoside. Furthermore, methyl 6-amino-6-deoxy-D-glucopyranoside proved to be an ihibitor for the enzymatic hydrolysis.

Escherichia coli↗
PubMed1991

Controlled reduction of acarbose: conformational analysis of acarbose and the resulting saturated products.

Saturation of the double bond in the non-reducing terminal unit of the tetrasaccharide amylase inhibitor, acarbose (1), with Raney nickel as the catalyst and at pH 8, gave 57% of a approximately 1:1 mixture of the 5a-carba-gluco (2) and -ido (3) isomers together with cleavage products including 26% of the trisaccharide 6-deoxy-alpha-D-Glcp4N-(1----4)-alpha-D-Glcp-(1----4)-D-Glc (4). The saturated compounds were isolated and characterised using 1H- and 13C-n.m.r. spectroscopy. The preferred conformations of 1 and 2 were dependent on the state of ionisation of the bridging nitrogen atom. The inhibition by 1-4 of the hydrolysis of methyl beta-maltoside by glucoamylase has been investigated; 1 and 2 were strong inhibitors.

Acarbose↗
PubMed1991

Conformational analysis of sialyloligosaccharides.

The conformational properties of several sialyloligosaccharides present as terminal sequences in N- and O-linked carbohydrate groups of glycoproteins, have been analyzed based on the n.m.r. data of selected sialosides. The compounds examined include representatives of the alpha-D-NeuAc-(2----6)-beta-D-Gal-(1----4)-beta-D-GlcNAc, alpha-D-NeuAc-(2----3)-beta-D-Gal-(1----4)-beta-D-GlcNAc, alpha-D-NeuAc-(2----3)-beta-D-Gal-(1----3)-beta-D-GlcNAc, and alpha-D-NeuAc-(2----3)-beta-D-Gal-(1----3)-beta-D-GalNAc series. Two deuterated sialosides were prepared by enzymic sialylation of 6-deuterated galactose derivatives of methyl beta-D-galactopyranoside and lactoside. These were useful for the unambiguous establishment of the "gt" orientation of the flexible C-6 methylene unit of the galactose through 1H-1H coupling constants. Of all the (2----6) sialosides examined, only the deuterated di- and tri-saccharide afforded useful nuclear Overhauser enhancement data that could be used to evaluate the global minimum-energy conformations. Hard-sphere exoanomeric effect calculations estimated the glycosidic torsion angles for the global minimum-energy conformer of alpha-D-NeuAc-(2----6)-beta-D-Gal linkages to be -163/-132/61 degrees (theta, psi, and omega, respectively). However, the potential energy well surrounding this global minimum was very shallow and indicated a broad population distribution of conformers. These are illustrated by the isoenergy contour maps. The observation of n.O.e. between the H-3ax and H-6R of the galactose in two deuterated (2----6) sialosides, indeed supported the presence of one of the global minimum-energy conformers. The conformational analysis carried out for the di- and trisaccharide [alpha-D-NeuAc-(2----6)-beta-D-Gal-OMe and alpha-D-NeuAc-(2----6)-beta-D-Gal-(1----4)-beta-D-Glc-OMe respectively] was then extended to sialoside linkages of other tri- and penta-saccharides by comparison of their 1H- and 13C-n.m.r. chemical shifts. HSEA calculations for the (2----3) sialosides indicated the potential energy well containing the global minimum energy-conformer (theta, psi = -160 +/- 4, -11 +/- 2 degrees) was deeper than the one estimated for the (2----6) sialosides. The n.O.e. data are consistent with the distribution of the majority of conformers around the lowest-energy one in solution. CPK models highlighting the topographical differences between the lowest-energy conformations of alpha-(2----6) and alpha-(2----3) sialosides are presented.

Carbohydrate Conformation↗
PubMed1991

Steric and electronic effects in the formation of dihexulose dianhydrides. Reaction of racemic sorbose in anhydrous hydrogen fluoride and a facile synthesis of D-sorbose.

Treatment of DL-sorbose with anhydrous hydrogen fluoride gave a high yield of alpha-D-sorbopyranose alpha-L-sorbopyranose 1,2':2,1'-dianhydride. Similarly a mixture of D-fructose and D-sorbose gave a good yield of beta-D-fructopyranose alpha-D-sorbopyranose 1,2':2,1'-dianhydride. The formation of these products compared to the more complicated mixtures of compounds obtained by treatment of L-sorbose or D-fructose with hydrogen fluoride, is discussed in terms of conformations, and steric and electronic factors.

Carbohydrate Conformation↗
PubMed1991

Assignment of structures to oligosaccharides produced by enzymic degradation of a beta-D-glucan from barley by 1H- and 13C-n.m.r. spectroscopy.

The structures of one tri-(1), two tetra-(2 and 3), and one hexa-saccharide (4) produced by treatment of barley flour, after removal of the starch components, with a fungal beta-D-glucanase (Finizyme) have been assigned on the basis of 1H- and 13C-n.m.r. data as follows: beta-D-Glcp-(1----3)-beta-D-Glcp-(1----4)-D-Glcp (1), beta-D-Glcp-(1----4)-beta-D-Glcp-(1----3)-beta-D-Glcp-(1----4)-D-Glcp (2), beta-D-Glcp-(1----3)-beta-D-Glcp-(1----4)-beta-D-Glcp-(1----4)-D-Glcp (3), and beta-D-Xylp-(1----4)-[alpha-L-Araf-(1----3)]-[alpha-L-Ara f-(1----2)-beta-D-Xylp-(1----4)-beta-D-Xylp- (1----4)-D-Xylp (4).

Carbohydrate Sequence↗
PubMed1991

A nuclear magnetic resonance spectroscopic and conformational study of eight pseudo-trehaloses (D-glucopyranosyl 5a-carba-D- and -L-glucopyranosides).

N.m.r. data (1H and 13C) are presented for eight pseudo-trehalose derivatives in which the D-glucopyranosyl moiety is alpha or beta and the 5a-carbaglucopyranoside moiety is alpha-D, beta-D, alpha-L, or beta-L. The differences in the chemical shifts and then n.O.e. effects have been correlated with the preferred conformations estimated from empirical force-field calculations (HSEA), which have been used to calculate the average parameters over the whole energy surface. Of the four alpha-D-glucopyranosyl derivatives, only that with a 5a-carba-beta-D-glucopyranoside moiety (3) was a substrate for glucoamylase.

Carbohydrate Conformation↗
PubMed1991

Broken agreement.

The subjects and verbs of English sentences agree in number. This superficially simple syntactic operation is regularly implemented by speakers, but occasionally derails in sentences such as The cost of the improvements have not yet been estimated. We examined whether the incidence of such errors was related to the presence of subject-like semantic features in the immediate preverbal nouns, in light of current questions about the semantic versus syntactic nature of sentence subjects and the interactivity of language processing. In three experiments, speakers completed sentence fragments designed to elicit erroneous agreement. We varied the number and animacy of the head noun and the immediate preverbal (local) noun, as well as the amount of material separating the head noun from the verb. The plurality of the local noun phrase had a large and reliable effect on the incidence of agreement errors, but neither its animacy nor its length affected their occurrence. The latter findings suggest, respectively, that the semantic features of sentence subjects are of minimal relevance to the syntactic and morphological processes that implement agreement, and that agreement features are specified at a point in processing where the eventual length of sentential constituents has little effect on syntactic planning. Both results follow naturally from explanations of language production that emphasize the segregation of sentence formulation processes into relatively autonomous components.

Adult↗
PubMed1991

Hydrolysis of substrate analogues catalysed by beta-D-glucosidase from Aspergillus niger. Part II: Deoxy and deoxyhalo derivatives of cellobiose.

The hydrolysis of sixteen mainly deoxy and deoxyhalo derivatives of celloboise catalysed by beta-D-glucosidase from Aspergillus niger has been studied by means of 1H NMR spectroscopy and progress-curve enzyme kinetics in both single-substrate and competition experiments. In the non-reducing ring of cellobiose it was found that the hydroxy groups at positions 2', 3', and 4' are essential for the enzymatic hydrolysis. The primary hydroxy group on 6' in this ring is, although important for the hydrolysis, not essential. The analogues modified at positions 3' and 4' and the 6'-bromo-6'-deoxy derivative were not inhibitors, whereas the 2'-deoxy derivative inhibited the enzymatic hydrolysis of methyl beta-cellobioside to some extent. Of the analogues modified in the reducing ring, some were hydrolysed faster (e.g. the deoxy compounds) and some slower than methyl beta-cellobioside in single-substrate experiments, but all derivatives were hydrolysed at a lower rate than this reference substrate in direct competition and displayed relatively weak inhibitory effects. The results are interpreted qualitatively with respect to changes in the free binding energies of the substrates and catalytic transition states based on the Michaelis-Menten mechanism, and some mechanistic implications of these findings are discussed.

Aspergillus niger↗
PubMed1990

Derivatives of methyl beta-lactoside as substrates for and inhibitors of beta-D-galactosidase from E. coli.

The 2'-,4'-, and 6'-deoxy derivatives of methyl beta-lactoside have been synthesised by deoxygenation at positions 2', 4', and 6', and the 3'-deoxy derivative was obtained by a glycosylation reaction. The 2'-O-methyl, 2'-O-benzyl, 2'-amino-2'-deoxy, and 1'-deuterio derivatives have been synthesized also. Only the 6'-deoxy and 1'-deuterio derivatives were substrates for the beta-D-galactosidase from E. coli, and the 2'-deoxy- and 2'-amino-2'-deoxy derivatives were potent inhibitors for the hydrolysis of methyl beta-lactoside by the enzyme.

Carbohydrate Sequence↗
PubMed1990

An n.m.r. and conformational analysis of the terminal trisaccharide from the serologically active glycolipid of Mycobacterium leprae in different solvents.

The 1H- and 13C-n.m.r. spectra of allyl 2-O-[4-O-(3,6-di-O-methyl-beta-D-glucopyranosyl)-2,3-di-O-methyl-alpha-L -rhamnopyranosyl]-3-O-methyl-alpha-L-rhamnopyranoside (3), a glycoside of the terminal trisaccharide found in the phenolic glycolipid I from Mycobacterium leprae, and those of the two component disaccharides, allyl 4-O-(3,6-di-O-methyl-beta-D-glucopyranosyl)-2,3-di-O- methyl-alpha-L-rhamnopyranoside (1) and allyl 2-O-(2,3-di-O-methyl-alpha-L-rhamnopyranosyl)-3-O-methyl-alpha-L- rhamnopyranoside (2) have been assigned completely by 1D and 2D techniques. The preferred conformations, determined by chemical shift and n.O.e. studies, were different in D2O, CD3OD, and CDCl3. The preferred conformation of 3 accorded with the results of hard-sphere exo-anomeric (HSEA) calculations.

Carbohydrate Conformation↗
PubMed1990

Framing sentences.

The sentence frames formed during language production are commonly and rather uncontroversially represented as hierarchical constituent structures. There is less accord about whether the frames are pure structural configurations or limnings of meaning. We examined these alternatives with a sentence priming paradigm in which the primes and targets shared phrase structures and event structures, or only phrase structures. The results of the first and second experiments indicated that event-structure changes had no impact on a reliable tendency to replicate the phrase structures of the primes within sentence targets. The last experiment showed that this tendency could not be attributed to metrical or to closed-class lexical similarities. The implication is that sentence frames are not identifiable with metrical or conceptual information, but are comparatively independent syntactic representations.

Adult↗
PubMed1990

Structure in language. Creating form in talk.

In psycholinguistics, the systematic study of language production has begun to take a place beside the study of language comprehension as a means to the end of understanding human language use. Because a major and very visible component of speaking a language is knowing how to create forms to carry messages, efforts to explain language production must confront long-standing questions about the relationship between structure and function in psychological explanation. One traditionally appealing view of that relationship in the realm of language is that sentence structures are associated with or reducible to the general forces of cognition that drive interpretation and communication. This article surveys some of the challenges to this view that emerge from the study of speech errors, and sketches the progress that has been made in developing an alternative view, renewing the argument that syntactic structures are necessary elements in an explanation of language use.

Adult↗
PubMed1990

Characterization of the surface layer glycoprotein of Clostridium symbiosum HB25.

The cell surface of Clostridium symbiosum HB25 is covered by a squarely arranged surface layer (S-layer) glycoprotein. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the sodium dodecyl sulfate-soluble whole-cell extract showed the presence of several high-molecular-weight protein bands in a narrow range (approximate Mr, 140,000) which, upon periodic acid-Schiff staining, gave a positive reaction. After proteolytic degradation of the purified S-layer glycoprotein, a single glycopeptide fraction was obtained by gel permeation chromatography. Hydrolysis, treatment with aqueous hydrofluoric acid, and 1H and 13C nuclear magnetic resonance studies showed that the glycoprotein glycan is a high-molecular-weight polymer (approximate Mr, 15,000) of tetrasaccharide repeating units with the component sugars N-acetylgalactosamine (GalNAc), N-acetylmannosamine (ManNAc), and N-acetylbacillosamine (BacNAc; 2-N-acetyl-4-amino-2,4,6-trideoxy glucose) linked by monophosphate diesters. The following structure is proposed: [----6)-alpha-D-ManpNAc-(1----4)-beta-D-GalpNAc-(1----3)-alpha-D-+ ++BacpNAc- (1----4)-alpha-D-GalpNAc-(1----PO3)----]n. The nuclear magnetic resonance data provided evidence for a charge interaction between the free amino group of BacNAc and the phosphate group of adjacent glycan chains. Since polycationic ferritin did not label the cell surface of intact cells, an electrostatic interaction can also be expected in vivo, leading to a charge-neutral outer surface, which is characteristic of all other S layers from members of the family Bacillaceae studied so far.

Amino Acids↗