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T Berg

Publications and source records attributed to T Berg.

At least 199 records · Page 11Linked to original sources
PubMed1992

Clearance of purified human liver gamma-glutamyltransferase after intravenous injection in the rat.

The clearance of gamma-glutamyltransferase was studied by injecting the purified human liver enzyme intravenously in the rat. The results show a biphasic clearance, with a rapid initial rate of removal. The initial uptake is more rapid for neuraminidase-treated GT. Liver accounts for the bulk organ uptake and the enzyme is almost exclusively taken up into the parenchymal cells. We suggest that the uptake of circulating GT is receptor mediated, most likely by the galactose receptor of the parenchymal cells.

Animals↗
PubMed1992

Characterization of a new kallikrein-like enzyme (KLP-S3) of the rat submandibular gland.

The submandibular gland of the rat contains several enzymes belonging to the kallikrein family. These include tissue kallikrein, antigen gamma (T-kininogenase), esterase B and tonin. In the present study, a new member of this family, which we have named KLP-S3, was identified and purified from the submandibular gland. KLP-S3 was classified as a kallikrein-like enzyme on the basis of its immunological similarity to other kallikrein-like enzymes and its showing 70% and 73% identity in partial amino acid sequence with tissue kallikrein and tonin respectively. Furthermore, the 44 sequenced amino acid residues showed complete correspondence to the mRNA S3 of the kallikrein gene family, which was the rationale for the name kallikrein-like protein (KLP) S3. KLP-S3 consisted of three isoenzymes with pI 6.75, 6.90 and 6.95, which significantly differed from those of other kallikrein-like enzymes. In conjunction with its immunological relationship to kallikrein, this parameter (pI) was considered robust enough to identify the enzyme during purification, since a specific physiological substrate for KLP-S3 has yet to be identified. In SDS/PAGE the three isoenzymes ran as one band with a molecular mass of 25,800 Da, which after reduction with 2-mercaptoethanol was split into two chains with molecular masses of 16,500 and 13,300 Da. In common with other kallikrein-like enzymes, KLP-S3 was inhibited by phenylmethanesulphonyl fluoride, and was thus classified as a serine protease. It was also inhibited by soya-bean trypsin inhibitor but not by aprotinin. It showed weak reactivity against the chromogenic substrates S2288, S2266, S2366 and S2302 (D-Ile-Pro-Arg 4-nitroanilide, D-Val-Leu-Arg 4-nitroanilide, Glu-Pro-Arg 4-nitroanilide and D-Pro-Phe-Arg 4-nitroanilide respectively) and did not cleave rat T-kininogen or dog high-molecular-mass/low-molecular-mass kininogen. Its specific angiotensin II-generating activity (angiotensin I as substrate) was 0.04% of that of rat tonin. KLP-S3 (1-100 nM) induced a statistically significant angiotensin-independent contraction of isolated rat aorta rings. The maximum contraction was 15% of the response to the alpha-adrenoceptor agonist phenylephrine (1 microM). The concentration of KLP-S3 in the rat submandibular gland was by single radial immunodiffusion estimated to be 47 +/- 3 micrograms/mg of protein.

Amino Acid Sequence↗
PubMed1992

Identification of proteins of the kallikrein family by isoelectrofocusing and immunoblotting.

We have found that kallikrein-like proteins differ in their isoelectric point but share antigenic determinants. For identification of kallikrein-like proteins an initial separation was carried out in flat-bed isoelectrofocusing gels. The kallikrein-like nature was demonstrated by an immunological similarity to kallikrein-like proteins by immunoblotting using antiserum against a kallikrein family member for staining. We used this system to identify different kallikrein-like proteins during purification of both known as well as new enzymes.

Amino Acid Sequence↗
PubMed1992

Productive and perceptual constraints on speech-error correction.

Two incentives underlie the present study on speech-error detection and correction. First, this area of research has up to now almost completely been approached through experimental techniques. Since it is not all clear whether speakers' detection and correction behaviour is identical inside and outside the laboratory, a comparison is made between experimental and naturalistic data. While the experimental materials are taken from the literature, the naturalistic findings are based upon the analysis of a corpus of more than 6,000 German slips of the tongue. It is shown that the same trends emerge in both data sets, thereby confirming the ecological validity of the experimental, and the reliability of the naturalistic, results. Secondly, the question arises as to the reasons for error correction and its occasional failure. Two working hypotheses are explored. Speakers fail to correct their errors because they have not detected them or because they assume that the error does not interfere with the listener's decoding process. The former reason is understood as a productive, the latter as a perceptual, constraint on the correction of self-produced errors. The empirical analysis discloses a large overlap between the effects of perceptual and productive constraints. However, whereas perceptual constraints can be subsumed under productive ones, the reverse is not possible. On the basis of this outcome it is argued that productive constraints are primary, and perceptual constraints secondary, reference points for error correction. Although the empirical data do not require the postulation of perceptual constraints, it is suggested that both speaker- and listener-based aspects form part of a highly integrated processing system.

Attention↗
PubMed1992

Load transfer by a maxillary distal-extension removable partial denture with cap and ring extracoronal attachments.

This study photoelastically compared the stress distribution characteristics of maxillary, bilateral, distal-extension removable partial dentures retained by light and heavy ERA extracoronal attachments. One prosthesis included supporting rests and the other had no rests. Both designs were tested with and without abutment splinting. The most favorable stress distributions were obtained with light retention elements, supporting rests, and splinting of the abutments. In this configuration the attachment prosthesis compared favorably in stress distribution with the maxillary I-bar retained removable partial denture in a previous study that used a comparable maxillae model.

Dental Prosthesis Retention↗
PubMed1992

Comparison of load transfer by maxillary distal extension removable partial dentures with a spring-loaded plunger attachment and I-bar retainer.

This study photoelastically compared the stress distribution characteristics of two maxillary bilateral distal-extension removable partial denture designs, one using I-bar retention and the other using a semiprecision spring-loaded plunger attachment. Each prosthesis was subjected to vertical and horizontal extension-base loads. Comparisons were made from photographic recordings of isochromatic fringe distributions. The two retention designs produced comparable stresses with splinting of abutments for the plunger attachment. The attachment-retained prosthesis proved less stable with some loadings. Stress patterns followed three trajectories in the maxilla. A basis for stress distribution comparisons to other maxillary removable partial denture attachments is established.

Analysis of Variance↗
PubMed1992

Phonological harmony as a processing problem.

This investigation focuses upon an outstanding aspect of child phonology--that of consonant harmony, relabelled 'phonological harmony'--and inquires whether representational or processing deficits are responsible for its occurrence. A detailed analysis of the oral output of one German-speaking girl (2;7.15-2;11) supports the contention that the Imperfect Processing Model fares much better in accounting for her harmony strategy than the Incomplete Representation Model. It is established that bilabial harmony is the only type of assimilation she has recourse to, and that this process is mainly used to cope with difficult sounds, although it also implicates consonants which do not pose a production problem. The difficult sounds are arguably not absent from the child's system because they can be uttered in some positions though not in others. The harmonizing tendency is interpreted within the interactive activation model of language production and is claimed to emanate from two particularities of her processing system. She has represented even the difficult elements as network nodes, but some connections between the segment and the feature level are ill developed. As a result, activation cannot spread smoothly between these levels and the relevant units cannot be made available for production. In addition, an excessive linkage strength has been built up among the node [bilabial] and all its associates at the segment level. This puts bilabial consonants into a state of hyperactivation and allows them even to intrude upon those segments which have been perfectly mastered. It is finally shown why these two mechanisms are very unlikely to become permanent features of the child's processing system.

Child Development↗
PubMed1992

Immunohistochemical localization of rat submandibular gland esterase B (homologous to the RSKG-7 kallikrein gene) in relation to other serine proteases of the kallikrein family.

The rat submandibular gland contains several members of the kallikrein family. In the present study we purified and raised an antiserum against one of these enzymes, i.e., esterase B, which was first described by Khullar et al. in 1986. N-terminal amino acid analysis revealed complete homology between esterase B and the kallikrein family gene RSKG-7. For characterization of the antiserum, flat-bed isoelectrofocusing with immunoblotting was superior to immunoelectrophoresis and double immunodiffusion in detecting and identifying crossreacting proteins. This was due to the fact that kallikrein-like enzymes were readily separated by isoelectrofocusing, and immunoreactivity was easily detected by the sensitive peroxidase-anti-peroxidase staining after blotting onto nitrocellulose membrane. Immunohistochemical controls were carried out accordingly, including homologous as well as crossreacting antigens. In the submandibular gland, esterase B was detected exclusively in all granular convoluted tubular cells, co-localized with tissue kallikrein and tonin. Some staining was also observed in striated duct cells; however, this staining reaction was induced by cross-reactivity with kallikrein, since staining was abolished by addition of kallikrein as well as esterase B to the primary antiserum. It was therefore concluded that like tonin and antigen gamma, but unlike kallikrein, esterase B was not detected in the striated ducts of the submandibular, parotid, or sublingual glands. This separation in anatomic distribution between esterase B and kallikrein may indicate that prokallikrein activation is not the only biological function of esterase B.

Amino Acid Sequence↗
PubMed1992

Role of liver endothelial and Kupffer cells in clearing low density lipoprotein from blood in hypercholesterolemic rabbits.

The role of liver endothelial and Kupffer cells in the hepatic uptake of cholesterol-rich low density lipoprotein (LDL) was studied in rabbits fed a diet containing 2% (w/w) cholesterol for 3 weeks. 125I-labeled tyramine cellobiose-labeled cholesterol-rich LDL was injected intravenously into rabbits, and parenchymal and nonparenchymal liver cells were isolated 24 h after injection. The hepatic uptake was 9 +/- 3% of injected dose in cholesterol-fed rabbits 24 h after injection, as compared to 36 +/- 9% in control-fed rabbits (n = 6 in each group; significant difference, P less than 0.005). Endothelial and Kupffer cells took up 2.7 +/- 0.5% and 1.2 +/- 0.8% of injected dose in the hypercholesterolemic rabbits, as compared to 1.9 +/- 0.8% and 0.8 +/- 0.3% in control animals. The amount accounted for by the parenchymal cells was markedly reduced in the cholesterol-fed rabbits to 7.3 +/- 2.7% of injected dose, as compared to 32.8 +/- 7.6% in controls (P less than 0.02). On a per cell basis, the nonparenchymal cells of cholesterol-fed rabbits took up as much LDL as the parenchymal cells (0.6 +/- 0.2, 0.7 +/- 0.1, and 0.6 +/- 0.4% of injected dose per 10(9) parenchymal, endothelial, and Kupffer cells, respectively). This is in marked contrast to the control animals, in which parenchymal cells took up about 6 times more LDL per cell than endothelial and Kupffer cells (3.2 +/- 0.9, 0.7 +/- 0.3, and 0.5 +/- 0.1% of injected dose per 10(9) cells). Thus, 30% of the hepatic uptake of LDL in the cholesterol-fed rabbits took place in nonparenchymal cells, as compared to 6% in controls. Consistent with these data, the concentrations of cholesteryl ester in endothelial and Kupffer cells in rabbits fed the high cholesterol diet were about twofold higher than in parenchymal cells (428 +/- 74 and 508 +/- 125 micrograms/mg protein, respectively, vs. 221 +/- 24 micrograms/mg protein in parenchymal cells). In contrast to cells from normal rabbits, Kupffer and endothelial cells from cholesterol-fed rabbits accumulated significant amounts of Oil Red O-positive material (neutral lipids). Electron microscopic examination of these cells in situ as well as in culture revealed numerous intracellular lipid droplets. Slot blot hybridization of RNA from liver parenchymal, endothelial, and Kupffer cells showed that cholesterol feeding reduced the level of mRNA specific for the apoB,E receptor to a small and insignificant extent in all three cell types (to 70-80% of that observed in control animals).(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1991

T-kininogenase activity of the rat submandibular gland is predominantly due to the kallikrein-like serine protease antigen gamma.

T-kininogen, the major kininogen in rat plasma, releases Ile-Ser-bradykinin (T-kinin) when incubated with trypsin, but is not a substrate for tissue kallikrein. Enzymes able to release T-kinins from T-kininogen have been found in the rat submandibular gland, but precise identification of these enzymes and their possible relationship to kallikrein-like enzymes has not been established. We studied T-kininogenase activity in fractionated submandibular gland homogenate. The main T-kininogen catalytic enzyme was purified and characterized, and found to be identical to antigen gamma, a kallikrein-like enzyme which we have previously characterized. Of other identified kallikrein-like enzymes only tonin showed weak T-kininogenase activity, which was about 0.25% of that of antigen gamma. No other T-kininogen catalytic enzymes were observed. Antigen gamma released a kinin which was identified as T-kinin by reverse-phase h.p.l.c. The T-kininogenase activity of antigen gamma had a Km of 29 +/- 4 microM and a kcat/Km of 140 M-1.s-1, and was comparable with its high and low molecular mass-kininogenase activity (7.4 and 10 micrograms of kinin/h per mg respectively). In contrast, tissue kallikrein released 0.2 and 42,200 micrograms of kinin/h per mg respectively. Thus antigen gamma is a weak kininogenase. The isoelectric point of antigen gamma, but not its molecular mass, differed from that of other kallikrein-like enzymes. Isoelectrofocusing in flat-bed gels combined with immunostaining was therefore a convenient method for identification. The kallikrein-like nature of antigen gamma was demonstrated by its immunological similarity to tissue kallikrein and tonin and by 91% and 87% amino acid sequence similarity with tonin and kallikrein respectively (67 amino acids sequenced). Complete identity was also not observed with other sequenced kallikrein genes, mRNAs or proteins.

Amino Acid Sequence↗
PubMed1991

Interactions of ricin with sinusoidal endothelial rat liver cells. Different involvement of two distinct carbohydrate-specific mechanisms in surface binding and internalization.

We have investigated the interactions of the plant toxin ricin with sinusoidal endothelial rat liver cells (EC). In these cells, ricin can be bound and internalized via either cell surface galactosyl residues or mannose receptors. Binding and uptake via galactosyl residues and mannose receptors was studied in the presence of mannan (1 mg/ml) and lactose (50 mM) respectively. Whereas most of the ricin binding was accounted for by cell surface galactosyl residues, uptake of ricin via mannose receptors was much more efficient than uptake via galactosyl residues. Internalized ricin is subject to extensive retroendocytosis (recycling to the cell surface from an early endocytic compartment). Retroendocytosis occurs after internalization of ricin via either pathway and to a much greater extent than for other glycoproteins taken up via mannose receptors of the EC. Hyperosmolarity (150 mM-sucrose), which is known to inhibit endocytosis from coated pits, strongly inhibited ricin uptake via mannose receptors, but had less effect on uptake via galactosyl residues. This suggests that only part of the galactose-specific uptake takes place from coated pits. Protein synthesis in EC was very sensitive to ricin [concn. causing half-maximal inhibition (IC50) = 1.3 x 10(-13) M]. Mannan was slightly more effective than lactose in protecting the EC protein synthesis from ricin toxicity.

Animals↗
PubMed1991

Parotid secretion of fluid, amylase and kallikrein during reflex stimulation under normal conditions and after acute administration of autonomic blocking agents in man.

The purpose of this work was to study the effect of graded mechanical and gustatory stimulation on the secretion of the acinar products fluid and amylase and the ductal product kallikrein from the human parotid gland (n = 9). The involvement of parasympathetic and sympathetic nerves in the salivary reflexes was subsequently examined using receptor blocking agents (n = 4). Chewing elevated the secretion of all products as compared to rest (P less than 0.013). When increasing the length of the chewing object, secretion of fluid (P less than 0.013), but not enzymes, further increased. The shift from mechanical to gustatory stimulation with 0.5% citric acid enhanced significantly the secretion of amylase and kallikrein (P less than 0.009), while application of 5.0% citric acid increased the secretion of both acinar products (P less than 0.009) more than kallikrein. A differentiated reflex control of salivation both with regard to input and output was thereby indicated. The muscarinic-cholinergic antagonist oxyphencyclimin reduced median fluid secretion between 54 and 76% depending on the stimuli. During citric acid stimulation, but not during chewing, fluid secretion was reduced about 40% by the beta 1-adrenergic antagonist metoprolol, and about 20% by the alpha 1-adrenergic antagonist prazosin. Median amylase secretion was reduced 30% during chewing and 75% during gustatory stimulation by metoprolol. It was concluded that the masticatory-salivary reflex mainly activated parasympathetic pathways producing saliva of low protein content.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1991

Lysosomal and endosomal heterogeneity in the liver: a comparison of the intracellular pathways of endocytosis in rat liver cells.

Air-filled albumin microspheres, asialoorosomucoid and formaldehyde-treated serum albumin are selectively taken up by endocytosis in rat liver Kupffer cells, parenchymal cells and endothelial cells, respectively. Intracellular transport and degradation of endocytosed material were studied by subcellular fractionation in sucrose and Nycodenz gradients after intravenous injection of the ligand. By using ligands labeled with 125I-tyramine-cellobiose, the subcellular distribution of labeled degradation products can be studied because they are trapped at the site of formation. The results show that the kinetics of intracellular transport are different in hepatic parenchymal, endothelial and Kupffer cells. In endothelial cells, the ligand is associated with two types of endosomes during the first minutes after internalization and then is transferred rapidly to the lysosomes. In parenchymal cells, 125I-tyramine-cellobiose-asialoorosomucoid was located in a relatively slowly sedimenting vesicle during the first minute after internalization and subsequently in denser endosomes. Degradation of 125I-tyramine-cellobiose-asialoorosomucoid in parenchymal cells started later than that of 125I-tyramine-cellobiose-formaldehyde-treated serum albumin in endothelial cells. Furthermore, the ligand seemed to be transferred relatively slowly from endosomes to lysosomes, and most of the undegraded ligand was in the endosomes. The rate-limiting step of proteolysis in parenchymal cells is probably the transport from endosomes to lysosomes. In Kupffer cells, most 125I-tyramine-cellobiose-microspheres are found as undegraded material in very dense endosomes up to 3 hr after injection. After 20 hr, most of the ligand is degraded in lysosomes distributed at a lower density than the endosomes in Nycodenz and sucrose gradients.

Albumins↗
PubMed1990

Transport and storage of vitamin A.

The requirement of vitamin A (retinoids) for vision has been recognized for decades. In addition, vitamin A is involved in fetal development and in the regulation of proliferation and differentiation of cells throughout life. This fat-soluble organic compound cannot be synthesized endogenously by humans and thus is an essential nutrient; a well-regulated transport and storage system provides tissues with the correct amounts of retinoids in spite of normal fluctuations in daily vitamin A intake. An overview is presented here of current knowledge and hypotheses about the absorption, transport, storage, and metabolism of vitamin A. Some information is also presented about a group of ligand-dependent transcription factors, the retinoic acid receptors, that apparently mediate many of the extravisual effects of retinoids.

Animals↗
PubMed1990

Receptor-mediated endocytosis of ovalbumin by two carbohydrate-specific receptors in rat liver cells. The intracellular transport of ovalbumin to lysosomes is faster in liver endothelial cells than in parenchymal cells.

1. The uptake of ovalbumin (OVA) in rat liver parenchymal cells (PC) and non-parenchymal cells was studied in vivo and in vitro in order to compare the cellular expression of glycoprotein receptors and the kinetics of intracellular transport of ligand endocytosed by these receptors. 2. Ovalbumin was labelled with 125I or with 125I-tyramine-cellobiose (125I-TC). By using 125I-TC-OVA the labelled degradation products were trapped in the cells. 3. 125I-TC-OVA was rapidly cleared from blood mainly by receptor-mediated uptake in the liver. At 30 min after injection, 50% of the ligand was recovered in the liver. The endothelial cells (EC) and the PC were the predominant cell types responsible for uptake. 4. The uptake in PC was strongly inhibited by asialo-orosomucoid (AOM), but not by mannan, indicating that the uptake in these cells was mediated by the galactose receptor and not by the mannose receptor. This finding is compatible with the observation that a proportion of the OVA contains terminal galactose residues in the carbohydrate moiety. 5. In vitro uptake of OVA in cultured EC was saturable and inhibited by mannan, mannose, fructose, N-acetylglucosamine, EDTA or monensin, but not by galactose or AOM. The uptake of OVA in these cells was therefore mediated by the mannose receptor. 6. To label the organelles involved in endocytosis in PC and EC, 125I-TC-OVA was injected intravenously together with an excess of either AOM or mannan. In this way the labelled ligand could be directed selectively to EC or PC respectively. Subcellular fractionation of total liver in sucrose and Nycodenz gradients revealed that in EC the intracellular transport of OVA is so fast that endocytosed ligand accumulates and thus increases the density of the lysosomes. Conversely, in PC transfer of ligand is slower, with the result that accumulation of undegraded ligand in the lysosomes does not occur. These findings are interpreted to mean that in EC the rate-limiting step of handling of endocytosed ligand is intralysosomal degradation, whereas in PC the rate-limiting step is transport of ligand to the lysosomes. 7. Altogether, these findings suggest that endocytosis of OVA by the liver EC and PC is mediated by mannose and galactose receptors respectively, and that the kinetics of intracellular transport of OVA differ in the two cell types.

Animals↗
PubMed1990

Intracellular transport of endocytosed proteins in rat liver endothelial cells.

1. Receptor-mediated endocytosis of mannose-terminated glycoproteins in rat liver endothelial cells has been followed by means of subcellular fractionation and by immunocytochemical labelling of ultrathin cryosections after intravenous injection of ovalbumin. For subcellular-fractionation studies the ligand was labelled with 125-tyramine-cellobiose adduct, which leads to labelled degradation products being trapped intracellularly in the organelle where the degradation takes place. 2. Isopycnic centrifugation in sucrose gradients of a whole liver homogenate showed that the ligand is sequentially associated with three organelles with increasing buoyant densities. The ligand was, 1 min after injection, recovered in a light, slowly sedimenting vesicle and subsequently (6 min) in larger endosomes. After 24 min the ligand was recovered in dense organelles, where also acid-soluble degradation products accumulated. 3. Immunocytochemical labelling of ultrathin cryosections showed that the ligand appeared rapidly after internalization in coated vesicles and subsequently in two larger types of endosomes. In the 'early' endosomes (1 min after injection) the labelling was seen closely associated with the membrane of the vesicle; after 6 min the ligand was evenly distributed in the lumen. At 24 min after injection the ligand was found in the lysosomes. 4. A bimodal distribution of endothelial cell lysosomes with different buoyant densities was revealed by centrifugation in iso-osmotic Nycodenz gradients, suggesting that two types of lysosomes are involved in the degradation of mannose-terminated glycoproteins in liver endothelial cells. Two populations of lysosomes were also revealed by sucrose-density-gradient centrifugation after injection of large amounts of yeast invertase. 5. In conclusion, ovalbumin is transferred rapidly through three endosomal compartments before delivering to the lysosomes. The degradation seems to take place in two populations of lysosomes.

Animals↗