bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of acidic pretreatment combined with a silane coupling agent on bonding durability to silicon oxide ceramic
Authors: Foxton Richard M. , Nakajima Masatoshi , Tagami Junji , Miura Hiroyuki 
Published: December 2004

AbstractThis study examined the effect of different acidic treatments and the role of a phosphate monomer in a silane coupling agent on the durability of the dual‐cure resin cement/silicon oxide bond. Ceramic blocks (Vita Celay Blanks) were cut into multiple 3 mm‐thick slices and polished using 600 grit SiC paper. Two pairs were left untreated [controls (CTRL)], two pairs were treated with 40% phosphoric acid and rinsed with water for 30 s (PA), and another two pairs treated with 20% hydrofluoric acid followed by 30 s water rinsing (HF). Half the specimens were silanated with Tokuso Ceramics Primer (TCP) (Tokuyama) and the other half with TCP formulated without phosphate monomer (TCP–NoPM). All the pairs were bonded with Bistite II dual‐cure resin cement (Tokuyama) and light cured. After 24 h water storage at 37°C, 0.7 mm‐thick slabs were serially sectioned. Immediately, after 6 months and after 1 year of water storage, two slabs were randomly selected from each subgroup, and sliced into beams (6 × 0.7 × 0.7 mm) for the microtensile bond strength (μTBS) test. The μTBS data were statistically analyzed using multiple Wilcoxon Signed Rank tests (p < 0.05). Failure modes were determined using a confocal laser‐scanning microscope. Ceramic surface morphology after the different acidic treatments was examined using an SEM. After 1 day, in the case of silane treatment with TCP, there were no significant differences in μTBS between the control and acid‐treated groups (p > 0.05), whereas with TCP–NoPM, the μTBS of the control was significantly lower than the acid‐treated groups (p < 0.05). All the TCP and acid‐treated TCP–NoPM groups exhibited significant reductions in μTBS after 6 months (p < 0.05). After 1 year, the μTBS of the acid‐treated TCP groups were not significantly different from the control TCP group (p > 0.05). There was also no significant difference between the HF‐treated TCP and TCP–NoPM groups (p > 0.05) after 1 year, all exhibiting greater than 10 MPa tensile bond strength. It is suggested that acidic pretreatment of the ceramic surface does not improve the durability of the dual‐cure resin cement/silicon oxide ceramic bond when an acidic phosphate monomer is present as an activator in a ceramic primer. © 2004 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 73B: 97–103, 2005
High α‐amylase activity in the syncytiotrophoblastic cells of first‐trimester human placentas
Authors: Fisher Susan J. , Laine Roger A. 
Published: December 2004

AbstractThe syncytiotrophoblastic brush border of the human placenta forms the maternal‐fetal interface and is an important determinant of placental function. Electron micrographs of fresh brush border preparations isolated from first‐trimester human placentas showed membrane vesicles, open‐ended microvilli, and numerous glycogen particles. Analysis of the microvillar membranes for several plasma and intracellular membrane markers showed a high degree of purification, comparable to the results reported for the isolation of microvilli from full‐term human placentas. The microvillar preparations from first‐trimester placentas, however, also contained the enzymes necessary to synthesize and degrade glycogen. The degradation resulted in the accumulation of maltotriose and maltotetraose, apparently due to the action of a liver‐type α‐amylase. The occurrence of this enzyme and the enzymes for synthesizing glycogen in this brush border fraction is probably associated with the necessity for an extremely active glucose transport and liver‐like storage system within the fetal tissue at this fetal‐maternal membrane interface.
Epidermal growth factor receptors on PC12 cells: Alteration of binding properties by lectins
Authors: Vale Ronald D. , Shooter Eric M. 
Published: December 2004

AbstractThe PC12 cell line displays cell surface receptors for both nerve growth factor (NGF) and epidermal growth factor (EGF). It has been previously shown that the lectin wheat germ agglutinin (WGA) alters the properties of NGF receptors on these cells. We now report that preincubations with either WGA or concanavalin A (Con A) decrease the binding of 125I‐EGF to PC12 cells by greater than 50%. The inhibition of binding occurred at 37°C and 4°C and could be blocked or reversed by the addition of sugars which bind specifically to WGA or Con A. Scatchard analysis revealed that these lectins decreased binding primarily by lowering the affinity of the receptor and to a lesser extent by decreasing receptor number. Succinylalion of Con A (sCon A) produced a derivative that was less effective than the native lectin in decreasing EGF binding; however, addition of an antibody against Con A restored the ability of sCon A to decrease binding. Similar to results obtained with 125I‐NGF binding, WGA but not Con A was found to increase, by scveralfold; the proportion of 125I‐EGF binding that is resistant to solubilization by Triton X‐100 detergent. A potential association of the EGF receptor with cytoskeletal elements is discussed which could account for such results.
Mitochondrial DNA of an African trypanosome
Authors: Stuart Kenneth 
Published: December 2004

AbstractThe maxicircles of African trypanosome kDNA are the genetic equivalent of other mitochondria! DNAs, but the function of minicircles is unknown. The maxicircle of Trypanosoma brucei 164 encodes conventional mitochondrial gene products and is largely but not completely transcribed. Nucleotide sequence analysis of a region not found to be transcribed revealed numerous translation termination codons in all three reading frames of both strands and numerous inverted repeats, suggesting that this segment does not have polypeptide‐coding function. This segment may encode a t‐RNA and has a sequence resembling a consensus sequence found in mitochondrial introns, thus implying that transcript processing occurs in trypanosome mitochondria. While several cloned minicircles had distinct restriction maps reflecting T brucei minicircle heterogeneity, one segment of the minicircle contained a sequence that was conserved by minicirclcs from other trypanosome strains and species. Of nine mutants unable to grow as the respiring procyclic forms, seven were devoid of kDNA. The other two mutants retained normal amounts of all maxicircle restriction fragments and normal amounts of those minicircle sequences tested. Minicircle alterations probably occur in these mutants, since the kDNA docs not stain with Giemsa and bands at an altered density in cesium chloride/ethidium bromide density gradients.
Killing of Giardia lamblia trophozoites by normal human milk
Authors: Gillin Frances D. , Reiner David S. , Wang Chi‐Sun 
Published: December 2004

AbstractThe clinical course of giardiasis is variable, and serum antibodies do not appear to be protective. We propose that natural factors either produced by intestinal tissue, transported into the intestine, or ingested (ie, by breast‐fed babies) might promote resistance to this disease. Human milk is very rich in secretory IgA (S‐IgA) antibodies, as well as nonspecific antibacterial factors (eg, lactoferrin, lysozyme).Previous studies showed that Giardia lamblia trophozoites were killed by nonimmune human milk (NHM) in a time‐ and concentration‐dependent manner. Removal of >99% of the S‐IgA from NHM did not decrease its Giardia‐cidal activity. Thus, the killing was not antibody dependent. This is the first demonstration of nonimmune antiparasitic defenses in human milk.The present studies show that in the presence of NHM, trophozoites lost motility, swelled, and lysed. The Giardia‐cidal activity (GCA) may be specific to human milk, since unhcated cow's and goat's milk were virtually devoid of activity. Much, but not all, of the GCA was lost when NHM was heated or reacted with diisopropylfluorophosphate (DIFP), a specific esterase inhibitor. Activity of the major human milk lipase (BSL, bile salt‐stimulated lipase, a fatty acid esterase) was lost after heat or DIFP treatment and was absent from cow's or goat's milk. The parasites were also killed by pure BSL. These studies suggest that BSL may be a heat‐labile Giardia‐cidal component of NHM.
Interaction of high‐density lipoprotein with Trypanosoma brucei: Effect of membrane stabilizers
Authors: Rifkin M. R. 
Published: December 2004

AbstractThe specific lysis of bloodstream trypanosomes by serum from a nonpermissive mammalian host is the result of interaction between the serum trypanocidal factor (high‐density lipoprotein) and the trypanosome surface. The studies described in this paper attempt to define further the mode of action of this cytotoxic lipoprotein. The binding of high‐density lipoprotein to Trypanosoma brucei was instantaneous at 4°C and readily reversible. Binding was not mediated by the surface glycoprotein as removal of the surface coat enhanced binding at 4°C, and no stable glycoprotein‐lipoprotein complex could be detected. Pretreatment of trypanosomes with the cross linker dimethylsuberimidate rendered cells resistant to lysis. Addition of membrane‐stabilizing drugs, such as cytochalasins C, D, and E, and local anesthetics (dibucaine, tetracaine, and procaine), also inhibited high‐density lipoprotein‐induced cell lysis. The data presented support the idea that at 37°C lateral diffusion of the variant surface glycoprotein, an integral membrane protein, allows maximal high‐density lipoprotein‐cell interaction in serum‐sensitive cells, and that altered properties of the plasma membrane induced by low temperature or the addition of cytochalasins, local anesthetics, or zinc inhibit this interaction, possibly by increasing the shielding of the plasma membrane by more rigidly anchored surface glycoprotein molecules.
The light‐dependent control of chloroplast development in barley (Hordeum vulgare L)
Authors: Apel Klaus , Gollmer Ingrid , Batschauer Alfred 
Published: December 2004

AbstractThe light‐induced greening of etiolated barley plants is used as a model to study the light‐dependent control of plastid development. Upon illumination a rapid transformation of etioplasts to chloroplasts is induced. The effect of illumination docs not only include the light‐dependent chlorophyll synthesis but also the appearance or decline of specific proteins within the plastid membrane fractions. So far two of these proteins have been studied in detail. The light‐harvesting chlorophyll a/b protein (LHCP) is one of the major protein constituents of the thylakoid membrane of chloroplasts. However, this protein is not detectable among the membrane polypeptides of etioplasts. Illumination of dark‐grown bar‐Icy plants induces a massive insertion of the LHCP, The appearance of the protein is controlled by the cooperation of at least two distinct photoreceptors: protochlorophyllide and phytochrome. In dark‐grown barley plants not only the LHCP but also its mRNA is not detectable. The light‐dependent appearance of mRNA activity for the LHCP is under the control of phytochrome (Pfr). Even though the appearance of mRNA activity is induced via Pfr by a single red light pulse, the assembly of the complete LHCP takes place only under continuous illumination, which allows chlorophyll synthesis. The second protein analyzed so far is the NADPH‐prolochlorophyllide‐oxidoreductase. This enzyme catalyzes the light‐dependent reduction of protochlorophyllide to chlorophyllide and thus controls one of the first detectable light‐dependent reactions during the greening period. It is generally assumed that this enzyme is responsible for the overall chlorophyll synthesis and accumulation during the greening period. In contrast to this hypothesis, we found a rapid decline of the enzyme during illumination. In addition to the decrease of the enzyme protein, the translatable mRNA coding for the enzyme also declines rapidly under the influence of light. Also this effect is mediated by phytochrome. Using cloned cDNA as hybridization probes we have demonstrated that the light‐induced changes of the two translatable mRNAs for the NADPH‐protochlorophyllide oxidoreductase and the LHCP are both paralleled by corresponding changes in the steady‐state concentration of the mRNA sequences. Thus, it seems likely that one major point of control at which phytochrome regulates the development of chloroplasts is the expression of genes at the level of transcription.
Substrate and phospholipid specificity of the purified mannitol permease of Escherichia coli
Authors: Jacobson Gary R. , Tanney Laura E. , Kelly Dori M. , Palman Karin B. , Corn Stephen B. 
Published: December 2004

AbstractD‐Mannitol is transported and phosphorylated by a specific enzyme II of the phosphotransferase system of Escherichia coli. This protein was purified previously in detergent solution and has been partially characterized. As one approach in understanding the structure and mechanism of this enzyme/pcrmease, we have tested a number of sugar alcohols and their derivatives as substrates and/or inhibitors of this protein. Our results show that the mannitol permease is highly, but not absolutely, specific for D‐mannitol. Compounds accepted by the enzyme include those with substitutions in the C‐2 (= C‐5) position of the carbon backbone of the natural substrate as well as D‐mannonic acid, one heptilol and one pentitol. All of these compounds were both inhibitors and substrates for the mannitol permease except for D‐mannoheptilol, which was an inhibitor but was not phosphorylated by the enzyme. No compound examined, however, exhibited an affinity for the enzyme as high as that for its natural substrate. We have also investigated the phospholipid requirements of the mannitol permease using phosphotipids purified from E coli. The purified protein was significantly activated by phosphatidylethanolamine, but little activation was observed with phosphatidylglycerol or cardioli‐pin. These observations partially delineate requirements for interaction of sugar alcohols and phospholipids with the mannitol permease. They suggest approaches for the design of specific active site probes for the protein, and strategies for stabilizing the enzyme's activity in vitro.
Granulocyte macrophage‐colony stimulating factor stimulates the synthesis of membrane and nuclear proteins in murine neutrophils
Authors: Stanley I. J. , Burgess A. W. 
Published: December 2004

AbstractThe effect of granulocyte macrophage‐colony stimulating factor (GM‐CSF), a well‐characterized hemopoietic regulator, on protein synthesis in murine bone marrow neutrophils is described. Bone marrow neutrophils in excess of 95% purity were obtained by fluorescence‐activated cell sorting.While GM‐CSF did not appear to slow the rate of dying of peritoneal exudate neutrophils or thymus cells, the viability of bone marrow neutrophils after 17 hr was enhanced (40%) by GM‐CSF. GM‐CFS had no effect on total 35S‐methionine incorporation by thymocytcs or peritoneal exudate neutrophils over a 17‐hr incubation period; however, bone marrow neutrophils showed increased incorporation (approximately 10%) at all times between 5–17 hr. As viability and 35S‐methionine incorporation of bone marrow neutrophils at 5 hr,were minimally affected by GM‐CSF, this time point was chosen to study the effect of GM‐CSF on the synthesis of particular proteins. Two‐dimensional polyacrylamide gels of 35S‐methionine‐labelled lysates were prepared from whole cells, isolated nuclei, and membranes. Quantitative analysis of the fluorograms obtained from the two‐dimensional electropherograms by a computer‐linked optical data digitiser indicated that out of a total of 180 proteins, the amount of label contained in 11 proteins was significantly higher in the presence of GM‐CSF, while.three proteins, apparently of cytoplasmic origin, contained less label than control cells. Eight of these proteins were identified as nuclear, and one was membrane derived. Attempts have been made to identify some of the inducible proteins and to correlate results with other studies of normal hemopoietic and Icukcmic cells. The significance and multiple functions of GM‐CSF in hemopoiesis are discussed.
The ubiquitin‐mediated proteolytic pathway and mechanisms of energy‐dependent intracellular protein degradation
Authors: Ciechanover Aaron , Finley Daniel , Varshavsky Alexander 
Published: December 2004

AbstractIn this review we briefly describe the lysosomal system, consider the evidence for multiplicity of protein degradation pathways in vivo, discuss in detail the ubiquitin‐mediated pathway of intracellular ATP‐dependent protein degradation, and also the possible significance of ubiquitin‐histone conjugates in chromatin. For detailed discussions of the various characteristics and physiological roles of intracellular protein breakdown, the reader is referred to earlier reviews [1–7] and reports of recent symposia [8–10]. Information on the ubiquitin system prior to 1981 was described in an earlier review [11]. Hershko has briefly reviewed more recent information [12].
Hepatocyte receptors for antithrombin III‐proteinase complexes
Authors: Fuchs Herbert E. , Shifman Mark A. , Michalopoulos George , Pizzo Salvatore V. 
Published: December 2004

AbstractThe in vivo clearance of antithrombin III‐proteinase complexes occurs via a specific and saturable pathway located on hepatocytes. We now report studies of the catabolism of antithrombin III‐proteinase complexes in vitro using rat hepatocytes in primary culture. Antithrombin III‐thrombin and trypsin complexes were prepared and purified to homogeneity. Ligand uptake by hepatocytes was concentration, temperature, and time dependent. Initial rate studies were performed to characterize the maximum rate of uptake, V, and apparent Michaelis constant Kapp. These studies yielded a V of 12.8 fmol/mg cell protein/min and a Kapp of 144 nM for antithrombin‐trypsin complexes. Competition experiments with antithrombin III, antithrombin III‐proteinase complexes, α2‐macroglobulin‐methylamine, asialoorosomucoid and the neoglycoproteins, fucosyl‐bovine serum albumin (BSA), N‐acetylglucosammyl‐BSA, and mannosyl‐BSA indicated that only antithrombin III‐proteinase complexes were recognized by the hepatocyte receptor. Uptake studies were performed at 37°C with 125I‐antithrombin III‐trypsin and analyzed by sodium dodecyl sulfate‐polyacrylamide gel electrophoresis (SDS‐PAGE) in conjunction with autoradiography. These studies demonstrate time‐dependent uptake and degradation of the ligand to low molecular weight peptides. In addition, there was a time‐dependent accumulation of a high molecular weight complex of ligand and a cellular protein. This complex disappeared when gels were performed under reducing conditions.
Secretion and degradation of mutant leucine‐specific binding protein molecules containing C‐terminal deletions
Authors: Landick Robert , Duncan James R. , Copeland Bruce R. , Nazos Penelope M. , Oxender Dale L. 
Published: December 2004

AbstractThe leucine‐specific binding protein (LS‐BP), a periplasmic component of the Escherichia coli high‐affinity leucine transport system, is initially synthesized in a precursor form with a 23 amino acid N‐terminal leader sequence that is removed during secretion of the protein into the periplasm. Using in vitro mutagenesis, deletion mutants of the LS‐BP gene have been constructed with altered or missing amino acid sequences in the C‐terminal portion of the protein. These altered binding proteins exhibited normal processing and secretion but were rapidly degraded in the periplasmic space. In the presence of an uncoupler of the transmembrane potential (CCCP) the precursor forms accumulated in the membrane and were protected from degradation. The altered binding proteins also were secreted by spheroplasts of E coli, after which they were easily detected.
Characterization of a 140Kd cell surface glycoprotein involved in myoblast adhesion
Authors: Chapman Ann E. 
Published: December 2004

AbstractTwo monoclonal antibodies that cause changes in the morphology of cultured chick myogenic cells have been described previously [8]. In this paper, these antibodies are shown to interact with the same 140Kd protein. The 140Kd protein has been further characterized as a cell‐surface glycoprotein by lactoperoxidase‐catalyzed iodinations and lectin affinity chromatography. The protein is resistant to digestion by trypsin and collagenase and has been shown to be unrelated to fibronectin by immunoprecipitation studies and by peptide mapping. A second protein, of approximately 170Kd MW; is also immunoprecipitated by the monoclonal antibodies. This protein is probably unrelated to the 140Kd protein since the peptide maps are quite distinct.
Replacement perfusion of cultured eucaryotic cells: A method for the accurate measurement of the rates of growth, protein synthesis, and protein turnover
Authors: Spanier Arthur M. , Clark William A. , Zak Radovan 
Published: December 2004

AbstractThe fractional rates of protein synthesis (ks) and degradation (kp) were studied in the myeloma cell line SP2/0‐AG14 grown at different rates (kg). Cells in spinner flask suspension cultures were maintained at constant cellular density for prolonged periods by replacement perfusion of labeling medium at a rate equivalent to the rate of growth. Total protein synthesis was calculated from the specific‐radioactivity of labeled L‐leucine in the precursor (medium) and cellular protein. Fractional synthesis rates determined by approach to equilibrium labeling were the same as those determined by equilibrium‐pulse labeling kinetics and pulse‐chase kinetics. The rate of protein degradation was determined from the established relationship kg = ks – kp. Protein synthesis rates remained constant over a threefold range in the rate of cell growth. At relatively slow growth rates (kg = 0.017/hr) turnover represented a major fraction of total synthesis (kp = 0.032/hr = 0.65ks). At rapid growth rates (kg = 0.058/hr) the value of kp was less than 0.005/hr. No major difference was observed between the ks determined for individual cellular proteins (separated by SDS‐polyacrylamide (7.5%) gel electro‐phoresis) from rapid‐ and slow‐growing cultures. Thus, with an invariable ks, any change in growth rate is due to an inverse change in the rate of turnover. Since turnover is the balance between synthesis and degradation and since synthesis is unchanging then changes in the growth rate of SP2/0‐AG14 should be due to changes in the rate of protein degradation. Experiments were therefore performed to determine the origin of the degradative machinery, ie, cytosolic or lysosomal; autolysis of prelabeled cellular protein (in vitro) was observed only at acidic pH (4.2) and WUS totally inhibited by addition of lcupcptin (10 μM) and pepstatin (2 μM), the specific inhibitors of lysosomal cathepsins B (L) and D, respectively. Since growth rate appears to be regulated by the alterations in the rate of protein degradation and degradation (in vitro) in SP2/0‐AG14 appearsto be lysosomal, then one should be able to alter the rate of cellular growth by interfering with rate of lysosomal proteolysis. Indeed, when the lysosomotropic amine NH 4Cl (10 mM) is added to cells growing with a kg of 0.018/hr ± 0.001 (ks = 0.050/hr ± 0.002) the growth rate increased to 0.051/hr ± 0.002 without change in the rate of protein synthesis (ks = 0.049/hr ± 0.003). It is suggested from our data that the cellular growth rate of SP2/0‐AG14 is regulated by the lysosomal apparatus; whether this regulation is itself regulated by either a specific compartmentalization of the lysosomal proteinases and/or their substrates or by endogenous protease inhibitors, should prove to be an exciting area for future investigation.