bluuebunny/crossref_metadata_2025_split huggingface dataset:
Flow rate defective boundary conditions in haemodynamics simulations
Authors: Veneziani A. , Vergara C. 
Published: December 2004

AbstractIn the numerical simulation of blood flow problems it might happen that the only available physical boundary conditions prescribe the flow rate incoming/outgoing the vascular district at hand. In order to have a well‐posed Navier–Stokes (NS) problem, these conditions need to be completed. In the bioengineering community, this problem is usually faced by choosing a priori a velocity profile on the inflow/outflow sections, that should fit the assigned flow rates. This approach strongly influences the accuracy of the numerical solutions. A less perturbative strategy is based on the so‐called ‘do‐nothing’ approach, advocated in Heywood et al. (Int. J. Num. Meth. Fluids 1996; 22:325–352). An equivalent approach, however, easier from the numerical discretization viewpoint, has been proposed in Formaggia et al. (SIAM J. Numer. Anal. 2002; 40(1):376–401). It is based on an augmented formulation of the problem, in which the conditions on the flow rates are prescribed in a weak sense by means of Lagrangian multipliers. In this paper we extend this analysis to the unsteady augmented NS problem, proving a well‐posedness result. Moreover, we present some numerical methods for solving the augmented problem, based on a splitting of the computation of velocity and pressure on one side and the Lagrangian multiplier on the other one. In this way, we show how it is possible to solve the augmented problem resorting to available NS solvers. Copyright © 2004 John Wiley & Sons, Ltd.
Comparative kinetics of phosphomannosyl receptor‐mediated pinocytosis of fibroblast secretion acid hydrolases and glycopeptides prepared from them
Authors: Fischer H. David , Creek Kim E. , Strisciuglio Pietro , Sly William S. 
Published: December 2004

AbstractIn a previous report we demonstrated that phosphorylated oligosaccharides isolated from acid hydrolases were subject to pinocytosis by phosphomannosyl receptors present on the cell surface of human fibroblasts [9]. However, limiting quantities of oligosaccharides precluded detailed comparison of the kinetics of pinocytosis of these phosphorylated oligosaccharides to those of the acid hydrolases from which they were derived. In this report we present studies comparing the kinetics of pinocytosis of acid hydrolases from NH4Cl‐induced fibroblast secretions with those of concanavalin A‐binding glycopeptides prepared from them by pronase digestion. The uptake of both secretion acid hydrolases and 125I‐labeled glycopeptides was linear for at least 3 hr, saturable, inhibited competitively by mannose 6‐phosphate, and destroyed by prior treatment of the ligand with alkaline phosphatase. The inhibition constants of excess unlabeled glycopeptide for the uptake of 125I‐labeled glycopeptides (Ki of 1.5 × 10−6 M) and for the uptake of secretion acid hydrolases (Ki of 2.2 × 10−6 M) were remarkably similar. Furthermore, the Ki for mannose 6‐phosphate inhibition of pinocytosis of glycopeptide uptake (3 × 10−5 M) compares closely to that previously determined for the pinocytosis of intact “high‐uptake” acid hydrolases (3–6 × 10−5 M).“High‐uptake” fractions of both ligands were prepared and quantified by affinity chromatography on immobilized phosphomannosyl receptors purified from bovine liver. Only 10% of the concanavalin A‐binding glycopeptides bound to the immobilized phosphomannosyl receptors, while 80% of the acid hydrolases from which they were prepared bound and were eluted with 10 mM mannose 6‐phosphate. However, the fraction of each type of ligand that binds to the immobilized phosphomannosyl receptors accounts for all the uptake activity of that ligand. The pinocytosis rates (% of added ligand internalized/mg protein/hr) of the “high‐uptake” fraction of both intact acid hydrolase (12%/mg/hr) and glycopeptide (6%/mg/hr) differed by only twofold. The apparent Kuprake for both ligands was of the same order of magnitude. The similarity in the kinetics of pinocytosis of the secreted acid hydrolases and of the phosphomannose‐bearing glycopeptides prepared from them suggests that the structural information which confers high‐affinity binding to the phosphomannosyl receptor is contained in the glycopeptide units themselves. No additional information from the intact protein backbone appears essential for phosphomannosyl receptor‐mediated pinocytosis.
Rotaviruses code for two types of glycoprotein precursors
Authors: Ericson Brad L. , Petrie Betty L. , Graham David Y. , Mason Bruce B. , Estes Mary K. 
Published: December 2004

AbstractRotaviruses are nonenveloped viruses that code for two glycoproteins: a structural glycoprotein (VP7) and a nonstructural glycoprotein (NS29). The precursor to VP7 (37K) was shown to contain a 1.5K cleavable signal sequence. The 37K precursor was authentically processed (signal sequence cleaved and the polypeptide “core” glycosylated) when synthesized in a cell‐free system supplemented with dog pancreatic microsomes. Similar experiments were performed with the nonstructural glycoprotein precursor (20K); however, the 20K precursor contained an integral (noncleavable) signal sequence. Both precursors were inserted into membranes cotranslationally and both glycosylated products underwent post‐translational oligosaccharide processing. The results suggest a morphogenetic scheme for the simian rotavirus SA11.
A simian virus 40‐encoded protein of Mr 74,000 daltons is structurally related to the capsid proteins of the virus
Authors: Krippl Bernd , Dreiseikelmann Brigitte , Werchau Hermann 
Published: December 2004

AbstractWe have demonstrated the synthesis of a 74,000‐dalton protein (74K protein) in African green monkey kidney cells infected with simian virus (SV)40. The 74K protein was detected late during the lytic cycle. Its synthesis was inhibited by arabinosyl cytosine as was the synthesis of the capsid proteins. Monospecific antibodies raised against VP1 and VP3 precipitated the structural proteins and the 74K protein. The 74K protein was not found in purified virions. Tryptic peptide analysis demonstrated that the 74K protein shares methionine‐ and serine‐containing peptides with VP1 and VP3 and thus is structurally related to the capsid proteins.
Cell cycle and cyclic AMP‐dependent phosphorylation of plasma membrane proteins p14 and p24: Defects in smooth surface transformed cells
Authors: Boman Bruce M. , Zschunke Michael A. , Scott Robert E. 
Published: December 2004

AbstractTwo proteins which are localized to the cytoplasmic surface of the plasma membrane, p14 and p24, undergo cyclic AMP‐dependent phosphorylation in rapidly growing nontransformed murine embryo cells. In this cell system, growth arrest in the G1 phase of the cell cycle induced by growth factor deprivation is associated with the reversible loss in ability to phosphorylate these substrates. By contrast Simian virus 40 and methylcholanthrene transformed cells show both defective G1 growth control and defects in their ability to phosphorylate p14 and p24 under all tested growth conditions. These data suggested a correlation between defects in the physophorylation of p14 and p24 and defects in the ability of transformed cells to G1 growth arrest. The results of the current studies by contrast show that 3T3 T proadipocytcs which have been transformed by the smooth surface tumorigenesis method show different characteristics. They retain the ability to G1 growth arrest in serum‐deficient medium. They show cyclic AMP‐dependent phosphorylation of p14 and p24 during exponential growth. They do not, however, down regulate p14 and p24 phosphorylation in association with G1 growth arrest. These observations suggest that neoplastic transformation is not necessarily associated with absolute defects in the ability to phosphorylate p14 and p24. Rather, the results of the current study suggest that the inability to modulate the cyclic AMP‐dependent phosphorylation of plasma membrane p14 and p24 proteins during the G1 phase of the cell cycle may be more tightly associated with neoplastic transformation.
A model for the structure of fumarate reductase in the cytoplasmic membrane of escherichia coli
Authors: Weiner Joel H. , Lemire Bernard D. , Jones Robert W. , Anderson Wayne F. , Scraba Douglas G. 
Published: December 2004

AbstractBy a recombinant DNA approach we have prepared Escherichia coli cytoplasmic membranes that are highly enriched in the terminal electron transfer enzyme fumarate reductase. This enzyme is composed of four nonidentical subunits in equal molar ratio. A 69,000‐dalton covalent flavin‐containing subunit and a 27,000‐dalton nonheme iron‐containing subunit make up a membrane extrinsic catalytic domain. Two very hydrophobic subunits of 15,000 and 13,000 daltons make up the hydrophobic membrane anchor domain. Electron microscopy of negatively stained membranes shows a characteristic knob‐and‐stalk‐type structure composed of the catalytic domain. The anchor polypeptides have been analyzed for hydrophobic segments and α‐helical content and a model for their organization within the lipid bilayer is presented. The results reviewed in this paper suggest a model for the fumarate reductase complex in the cytoplasmic membrane
Light regulation of photosynthetic membrane structure, organization, and function
Authors: Melis Anastasios 
Published: December 2004

AbstractThe light environment during plant growth determines the structural and functional properties of higher plant chloroplasts, thus revealing a dynamically regulated developmental system. Pisum sativum plants growing under intermittent illumination showed chloroplasts with fully functional photosystem (PS) II and PSI reaction centers that lacked the peripheral chlorophyll (Chi) a/b and Chl a light‐harvesting complexes (LHC), respectively. The results suggest a light flux differential threshold regulation in the biosynthesis of the photosystem core and peripheral antenna complexes. Sun‐adapted species and plants growing under far‐red‐depleted illumination showed grana stacks composed of few (3–5) thylakoids connected with long intergrana (stroma) thylakoids. They had a PSII/PSI reaction center ratio in the range 1.3–1.9. Shade‐adapted species and plants growing under far‐red‐enrichcd illumination showed large grana stacks composed of several thylakoids, often extending across the entire chloroplast body, and short intergrana stroma thylakoids. They had a higher PSII/PSI reaction center ratio, in the range of 2.2–4.0. Thus, the relative extent of grana and stroma thylakoid formation corresponds with the relative amounts of PSII and PSI in the chloroplast, respectively. The structural and functional adaptation of the photosynthetic membrane system in response to the quality of illumination involves mainly a control on the rate of PSII and PSI complex biosynthesis.
The detergent solubility properties of a malarial (Plasmodium knowlesi) variant antigen expressed on the surface of infected erythrocytes
Authors: Howard Russell J. , Barnwell John W. 
Published: December 2004

AbstractFour detergents have been compared for identification of the Plasmodium knowlesi variant antigen on infected erythrocytes by immunoprecipitation analysis. Erythrocytes infected with late trophozoite and schizont forms of cloned asexual parasites were labeled by lactoperoxidase‐catalyzed radioiodination and extracted either with the anionic detergents sodium dodecyl sulfate (SDS) or cholate, the neutral detergent Triton X‐100, or the zwitterion 3‐[(3‐cholamidopropyl)di‐methylammonio]‐1‐propane sulfonate (CHAPS). After addition of Triton X‐100 to SDS and cholate extracts, parallel immunoprecipitations of the four extracts were performed using rhesus monkey antisera of defined agglutinability. Identical results were obtained with clone Pkl(A+ ), which has 125I‐variant antigens of Mr 210,000 and 190,000, and with clone Pkl(B+)l+, which hasvariant antigens of Mr 200,000–205,000. SDS yielded maximal levels of immunoprecipitated 125I‐variant antigens. Variant‐specific immunoprecipitation was detected in some experiments with Triton X‐100 and cholic acid but with significantly lower recovery than with SDS. CHAPS extraction did not yield the variant antigens on immunoprecipitation. The variant antigens could also be identified in Triton X‐100‐insoluble material by subsequent extraction with SDS, indicating that failure to recover these proteins in the Triton X‐100‐soluble fraction is due to failure of this detergent to extract the variant antigens rather than to degradation during extraction. We suggest that the 125I‐variant antigens either have a structure that renders them intrinsically insoluble in Triton X‐100, cholate, or CHAPS, or that they are associated in some way with host cell membrane components that also resist solubilization by these detergents.
Detergent dissociation of bovine liver phosphomannosyl binding protein
Authors: Mitchell Diane C. , Maler Thomas , Jourdian George W. 
Published: December 2004

AbstractWe have reported previously the isolation and partial characterization of a 215‐kilodalton (Kd) phosphomannosyl binding protein from bovine liver membranes [3,9]. In the present studies evidence is presented that the binding protein is an aggregate. Four N‐terminal amino acids were detected, and the complex could be dissociated into subunits.Bovine liver membranes were extracted with the detergent, Zwittergent, in the presence of protease inhibitors. The extract was subjected to affinity chromatography on phosphomannan‐Sepharose 4B, and proteins with apparent Mr values of 215 and 57 Kd were eluted with mannose 6‐phosphate. As reported previously, extraction with Triton X‐100 yielded only the higher molecular weight material. When the binding protein was incubated at 4°C in the presence of Zwittergent TM 3‐14 the 215‐Kd form slowly dissociated into smaller subunits; after two months, the major species had an apparent Mr of 57 Kd. The subunits derived from the binding protein were recognized by antiserum raised against purified binding protein. Dissociation of the binding protein by Zwittergent was enhanced by incubation at 37°C, the presence of dithiothreitol, and low pH values. The subunit mixture enriched in the 57‐Kd subunit had a lowered ability to bind ligands containing the phosphomannosyl recognition marker. Binding was partially restored (>48% of the initial value) when dissociated receptor was back exchanged with Triton X‐100.
Stimulation by glutamine of the formation of N6‐hydroxylysine in a cell‐free extract from aerobacter aerogenes 62‐1
Authors: Jackson G. E. D. , Parniak M. A. , Murray G. J. , Viswanatha T. 
Published: December 2004

AbstractGlutamine may serve as an activator and/or regulator of the N6‐hydroxylase (E.C. 1.14.99) of Aerobacter aerogenes 62‐1. Activation and stabilization of N6‐hydroxylase activity was observed both in vivo and in vitro. Growth in a glutamine‐supplemented medium resulted in (1) maximum N6‐hydroxylase activity at an earlier stage of growth and (2) higher N6‐hydroxylase activity and continued aerobactin synthesis into stationary phase. Storage of P2 in the presence of L‐glutamine (1 mM) significantly increased the lifetime of the labile N6‐hydroxylase activity. Inclusion of L‐glutamine in the incubation mixture typically resulted in a 2‐3‐fold activation of the hydroxylase activity. The stimulatory effect of glutamine was independent of and additive to the enhancement of N6‐hydroxylation by the active component(s) in the supernatant, S2 fraction. Glutamic acid‐γ‐semihydrazide activated slightly in the absence of glutamine but activation of the system by glutamine was decreased by this compound. Azaserine was shown to be an uncompetitive inhibitor with respect to lysine and this inhibition was not reversed by glutamine.
Characterization of thermotropic structural transitions of the erythrocyte membrane: A biochemical and electron‐paramagnetic resonance approach
Authors: Minetti Maurizio , Ceccarini Marina , Maria Anna , Di Stasi M. 
Published: December 2004

AbstractThe relationship between membrane structural properties and functions has been generally inferred from observed thermotropic phenomena. By the use of 16‐dinyloxyl stearic acid spin probe we investigated the red blood cell membrane components involved in three characteristic thermotropic structural transitions occurring at 8, 20, and 40°C. The transition at 8°C is removed by chymotrypsin treatment at the cytoplasmic membrane layer. The 20°C phase transition is unmodified after chymotrypsin treatment and occurs at 15°C after complete proteolysis of intramembranc chymolrypsin insensitive peptides. Liposomes from the total lipid extract of RBC show only one thermotropic transition at 15°C. The 40°C phase transition is absent in vesicles free of skeletal proteins, in vesicles obtained after RBC storage, and in low‐ionic‐strength resealed ghosts. Transitions at 8°C and 40°C appear to be due to the interactions of cytoplasmic exposed proteins with membrane, whereas the 20°C transition is intrinsic to the lipid component.
Amino acid pools in cultured muscle cells
Authors: Low Robert B. , Stirewalt William S. , Rittling Susan R. , Woodworth Robert C. 
Published: December 2004

AbstractCompartmentalization of cellular amino acid pools occurs in cultures of cardiac and skeletal muscle cells, but the factors involved in this are not clear. We have further defined this problem by analyzing the intracellular free leucine and the transfer‐RNA‐(tRNA)‐bound leucine pool in cultures of skeletal and cardiac muscle incubated with 3H‐leucine in the presence and absence of serum and amino acids. Withdrawal of nitrogen substrates caused substantial changes in leucine pool relationships–in particular, a change in the degree to which intracellular free leucine and tRNA‐leucine were derived from the culture medium. In separate experiments, the validity of our tRNA measurements was confirmed by measurements of the specific activity of newly synthesized ferritin after iron induction. We discuss the implications of these findings with regard‐to factors involved in the control of amino acid flux through the cell, as well as with regard to design of experiments using isotopic amino acids to measure rates of amino acid utilization.
Oncogenes: Growth regulation and the papovaviruses polyoma and SV40
Authors: Smith Alan E. 
Published: December 2004

AbstractCellular oncogenes and their activated and retrovirus‐coded counterparts play an important role in cellular regulation. Here the relationship between such oncogenes and the genes coding for the transforming proteins of the papovaviruses, polyoma viruses, and simian virus 40 (SV40) is discussed. It is concluded that polyoma virus may transform established cells by a mechanism involving activation of a cellular oncogene product, whereas SV40 may transform by a mechanism involving a previously little studied cytoplasmic form of the transforming protein.
Phosphorylation of the solubilized insulin receptor by the gene product of the Rous sarcoma virus, pp60src
Authors: White Morris F. , Kahn C. Ronald , Werth Diane K. , Pastan Ira 
Published: December 2004

AbstractBoth the insulin receptor and the gene product of the Rous sarcoma virus, pp60src, are protein kinases which phosphorylate themselves and other proteins on tyrosinc residues. Addition of the solubilized insulin receptor to purified pp60src increased the phosphorylation of the β‐subunit of the insulin receptor. Phosphorylation of the insulin receptor by pp60src occurred both in the absence and presence of insulin but did not alter the insulin dose response for autophosphorylation of the receptor. Increasing concentrations of pp60src increased the phosphorylation of the receptor and at high concentrations equaled the maximal effect produced by insulin. Our observations suggest a possible mechanism by which the metabolically regulated insulin receptor tyrosine kinase could be altered by other tyrosine kinases such as that associated with pp60src. Further studies will be required to determine if the insulin receptor is phosphorylated by pp60src in Rous sarcoma virus‐infected cells.
Studies on the biosynthesis of cartilage proteoglycan in a model system of cultured chondrocytes from the Swarm rat chondrosarcoma
Authors: Kimura James H. , Lohmander L. Stefan , Hascall Vincent C. 
Published: December 2004

AbstractBiosynthesis of cartilage proteoglycan was examined in a model system of cultured chondrocytes from a transplantable rat chondrosarcoma. Extensive modification with the addition of chondroitin sulfate glycosaminoglycan, N‐linkcd oligosac‐charide, and O‐linked oliogosaccharide is required to convert a newly synthesized core protein precursor into a proteoglycan. Kinetic analyses revealed the presence of a large pool of core protein precursor (t1/2 ∼ 90 min) awaiting completion into proteoglycan. The large t1/2 of this pool allowed kinetic labeling experiments with a variety of radioactive precursors to distinguish between early biosynthetic events associated primarily with the rough endoplasmic reticulum from late events associated primarily with the Golgi apparatus. The results of a series of experiments indicated that the addition of N‐linked oligosaccharide chains occurs early in the biosynthetic process in association with the rough endoplasmic reticulum, whereas the initiation and completion of O‐linked oligosaccharides occurs much later, at about the same time as chondroitin sulfate synthesis. This also indicated that keratan sulfate chains, when present in the completed molecule, are added in the Golgi apparatus, as they are probably built on oligosaccharide primers closely related to the O‐oligosaccharide chains. Furthermore, when 3H‐glucose was used as the precursor, the entry of label into xylose, the linkage sugar between the core protein and the chondroitin sulfate chain, was found to occur within 5 min of the entry of label into galactose and galactosamine in the remainder of the chondroitin sulfate chain. This indicated that the initiation and completion of the chondroitin sulfate chain occurs late in the pathway probably entirely in the Golgi apparatus. Thus, proteoglycan synthesis can be described as occurring in two stages in this system, translation and N‐glycosylation of a core protein precursor which has a long half‐life in the rough endoplasmic reticulum, followed by extensive rapid modification in the Golgi complex in which the majority of glycosaminoglycan and oligosaccharide chains are added to the core protein precursor with subsequent rapid secretion into the extracellular matrix.
Metabolic properties of an azaguanine‐resistant variant of Chinese hamster ovary cells (azarts) with normal levels of hypoxanthine‐guanine phosphoribosyltransferase activity
Authors: Plagemann Peter G. W. , Wohlhueter Robert M. 
Published: December 2004

AbstractAzarts Chinese hamster ovary cells were 20 to 50 times more resistant to 8‐amaguanine and 50 to 10 times more resistant to both 6‐thioguanine and 6‐mercaptopurine than wild‐type cells. Resistance correlated with a failure of azarts cells to incorporate 8‐amaguanine into the nucleotide pool and into nucleic‐acids. The uptake of hypoxanthine and guanine, on the other hand, was about the same in both types of cells and the hypoxanthine‐guanine phosphoribosyltransferase of the azarts cells as measured in cell lysates was unaltered both in concentration and kinetic properties with hypoxanthine as well as 8‐azaguanine as substrate. Plasma membrane permeability to 8‐azaguanine and the regulation of intracellular pH were also not altered in azarts cells and there was no significant degradation of 8‐azaguanine or azaguanine nucleotides. We conclude therefore that in azarts cells the phosphoribosylation of 8‐azaguanine per se is specifically blocked but that this effect is abolished upon cell lysis.