bluuebunny/crossref_metadata_2025 huggingface dataset:
On the Continuous Fermat-Weber Problem
Authors: Fekete Sándor P. , Mitchell Joseph S. B. , Beurer Karin
Published: February 2005

We give the first exact algorithmic study of facility location problems that deal with finding a median for a continuum of demand points. In particular, we consider versions of the “continuous k-median (Fermat-Weber) problem” where the goal is to select one or more center points that minimize the average distance to a set of points in a demand region. In such problems, the average is computed as an integral over the relevant region, versus the usual discrete sum of distances. The resulting facility location problems are inherently geometric, requiring analysis techniques of computational geometry. We provide polynomial-time algorithms for various versions of the L1 1-median (Fermat-Weber) problem. We also consider the multiple-center version of the L1 k-median problem, which we prove is NP-hard for large k.
Stochastic Transportation-Inventory Network Design Problem
Authors: Shu Jia , Teo Chung-Piaw , Shen Zuo-Jun Max
Published: February 2005

We study the stochastic transportation-inventory network design problem involving one supplier and multiple retailers. Each retailer faces some uncertain demand, and safety stock must be maintained to achieve suitable service levels. However, risk-pooling benefits may be achieved by allowing some retailers to serve as distribution centers for other retailers. The problem is to determine which retailers should serve as distribution centers and how to allocate the other retailers to the distribution centers. Shen et al. (2003) formulated this problem as a set-covering integer-programming model. The pricing problem that arises from the column generation algorithm gives rise to a new class of the submodular function minimization problem. In this paper, we show that by exploiting certain special structures, we can solve the general pricing problem in Shen et al. efficiently. Our approach utilizes the fact that the set of all lines in a two-dimension plane has low VC-dimension. We present computational results on several instances of sizes ranging from 40 to 500 retailers. Our solution technique can be applied to a wide range of other concave cost-minimization problems.
An Adaptive Sampling Algorithm for Solving Markov Decision Processes
Authors: Chang Hyeong Soo , Fu Michael C. , Hu Jiaqiao , Marcus Steven I.
Published: February 2005

Based on recent results for multiarmed bandit problems, we propose an adaptive sampling algorithm that approximates the optimal value of a finite-horizon Markov decision process (MDP) with finite state and action spaces. The algorithm adaptively chooses which action to sample as the sampling process proceeds and generates an asymptotically unbiased estimator, whose bias is bounded by a quantity that converges to zero at rate (ln N)/N, where N is the total number of samples that are used per state sampled in each stage. The worst-case running-time complexity of the algorithm is O((|A|N)H), independent of the size of the state space, where |A| is the size of the action space and H is the horizon length. The algorithm can be used to create an approximate receding horizon control to solve infinite-horizon MDPs. To illustrate the algorithm, computational results are reported on simple examples from inventory control.
Order-Based Cost Optimization in Assemble-to-Order Systems
Authors: Lu Yingdong , Song Jing-Sheng
Published: February 2005

We study a multi-item stochastic inventory system in which customers may order different but possibly overlapping subsets of items, such as a multiproduct assemble-to-order system. The goal is to determine the right base-stock level for each item and to identify the key driving factors. We formulate a cost-minimization model with order-based backorder costs and compare it with the standard single-item, newsvendor-type model with item-based backorder cost. We show that the solution of the former can be bounded by that of the latter with appropriately imputed parameters. Starting with this upper bound, the optimal base-stock levels of the order-based problem can be obtained in a greedy fashion. We also show that the optimal base-stock levels increase in replenishment lead times but may increase or decrease in lead-time variability and demand correlation. Finally, we devise closed-form approximations of the optimal base-stock levels to see more clearly their dependence on the system parameters.
Navy Personnel Planning and the Optimal Partition
Authors: Holder Allen
Published: February 2005

One could argue that the Navy's most important resource is its personnel, and as such, workforce planning is a crucial task. We investigate a new model and solution technique that is designed to aid in optimizing the process of assigning sailors to jobs. This procedure attempts to achieve an increased level of sailor satisfaction by providing a list of possible jobs from which a sailor may choose. We show that the optimal partition provided by an interior-point algorithm is particularly useful when designing the job lists. This follows because a strictly complementary solution to the linear programming relaxation observes all possible optimal solutions to the original binary problem. The techniques developed rely on a continuous parametric analysis, and we show that the parameterization provides meaningful information about the structure of the optimal assignments.
On the Asymptotic Optimality of the Gradient Scheduling Algorithm for Multiuser Throughput Allocation
Authors: Stolyar Alexander L.
Published: February 2005

We consider the model where N queues (users) are served in discrete time by a generalized switch. The switch state is random, and it determines the set of possible service rate choices (scheduling decisions) in each time slot. This model is primarily motivated by the problem of scheduling transmissions of N data users in a shared time-varying wireless environment, but also includes other applications such as input-queued cross-bar switches and parallel flexible server systems.

The objective is to find a scheduling strategy maximizing a concave utility function H(u1,…,uN), where uns are long-term average service rates (data throughputs) of the users, assuming users always have data to be served.

We prove asymptotic optimality of the gradient scheduling algorithm (which generalizes the well-known proportional fair algorithm) for our model, which, in particular, allows for simultaneous service of multiple users and for discrete sets of scheduling decisions. Analysis of the transient dynamics of user throughputs is the key part of this work.
Selecting Attributes to Measure the Achievement of Objectives
Authors: Keeney Ralph L. , Gregory Robin S.
Published: February 2005

The foundation for any decision is a clear statement of objectives. Attributes clarify the meaning of each objective and are required to measure the consequences of different alternatives. Unfortunately, insufficient thought typically is given to the choice of attributes. This paper addresses this problem by presenting theory and guidelines for identifying appropriate attributes. We define five desirable properties of attributes: they should be unambiguous, comprehensive, direct, operational, and understandable. Each of these properties is discussed and illustrated with examples, including several cases in which one or more of the desirable properties are not met. We also present a decision model for selecting among the different types of natural, proxy, and constructed attributes.
Chiral stationary phase covalently bound with a chiral pseudo‐18‐crown‐6 ether for enantiomer separation of amino compounds using a normal mobile phase
Authors: Hirose Keiji , Yongzhu Jin , Nakamura Takashi , Nishioka Ryota , Ueshige Tetsuro , Tobe Yoshito
Published: February 2005

In order to apply the excellent chiral recognition ability of chiral pseudo‐18‐crown‐6 ethers that we developed to chiral separation, we prepared a chiral stationary phase (CSP) by immobilizing a chiral pseudo‐18‐crown‐6‐type host on 3‐aminopropyl silica gel. A chiral column was prepared by the slurry‐packing method in a stainless steel HPLC column. A liquid chromatography system using this CSP combined with the detection by mass spectrometry was used for enantiomer separation of amino compounds. A normal mobile phase can be used on this CSP as opposed to conventional dynamic coating‐type CSPs. Enantiomers of 18 common natural amino acids were efficiently separated. The chiral separation observed for amino acid methyl esters, amino alcohols, and lipophilic amines was fair using this HPLC system. In view of the correlation between the enantiomer selectivity observed in chromatography and the complexion in solution, the chiral recognition in host–guest interactions might contribute to this enantiomer separation. Chirality 17:142–148, 2005. © 2005 Wiley‐Liss, Inc.
Maintenance of gene expression patterns
Authors: Brock Hugh W. , Fisher Cynthia L.
Published: February 2005

In development, cells pass on established gene expression patterns to daughter cells over multiple rounds of cell division. The cellular memory of the gene expression state is termed maintenance, and the proteins required for this process are termed maintenance proteins. The best characterized are proteins of the Polycomb and trithorax Groups that are required for silencing and maintenance of activation of target loci, respectively. These proteins act through DNA elements termed maintenance elements. Here, we re‐examine the genetics and molecular biology of maintenance proteins. We discuss molecular models for the maintenance of activation and silencing, and the establishment of epigenetic marks, and suggest that maintenance proteins may play a role in propagating the mark through DNA synthesis. Developmental Dynamics 232:633–655, 2005. © 2005 Wiley‐Liss, Inc.
A structural basis of light energy and electron transfer in biology
Authors: Huber Robert
Published: February 2005

Aspects of intramolecular light energy and electron transfer will be discussed for three protein cofactor complexes, whose three-dimensional structures have been elucidated by x-ray crystallography: Components of light harvesting cyanobacterial phycobilisomes, the purple bacterial reaction centre, and the blue multi-copper oxidases. A wealth of functional data is available for these systems which allow specific correlations between structure and function and general conclusions about light energy and electron transfer in biological materials to be made.
Membrane-Membrane contact: Involvement of interfacial instability in the generation of discrete contacts
Authors: Coakley W. T. , Gallez D.
Published: February 2005

The classical approach to understanding the closeness of approach of two membranes has developed from consideration of the net effect of an attractive van der Waals force and a repulsive electrostatic force. The repulsive role of hydration forces and stereorepulsion glycocalyx forces have been recently recognized and an analysis of the effect of crosslinking molecules has been developed. Implicit in these approaches is the idea of an intercellular water layer of uniform thickness which narrows but retains a uniform thickness as the cells move towards an equilibrium separation distance. Most recently an attempt has been made to develop a physical chemical approach to contact which accommodates the widespread occurrence of localized spatially separated point contacts between interacting cells and membranes. It is based on ideas drawn from analysis of the conditions required to destabilize thin liquid films so that thickness fluctuations develop spontaneously and grow as interfacial instabilities to give spatially periodic contact. Examples of plasma membrane behaviour which are consistent with the interfacial instability approach are discussed and experiments involving polycation, polyethylene glycol, dextran and lectin adhesion and agglutination of erythrocytes are reviewed.
The effect of extracellular calcium elevation on morphology and function of isolated rat osteoclasts
Authors: Datta Harish K. , MacIntyre Iain , Zaidi Mone
Published: February 2005

Osteoclasts are large multinucleate cells unique in their capacity to resorb bone. These cells are exposed locally to high levels of ionised calcium during the process of resorption. We have therefore examined the effect of elevated extracellular calcium on the morphology and function of freshly disaggregated rat osteoclasts. Cell size and motility were quantitated by time-lapse video recording together with digitisation and computer-centred image analysis. In order to assess the resorptive capacity of isolated osteoclasts, we measured the total area of resorption of devitalised cortical bone by means of scanning electron microscopy and computer-based morphometry. The results show that elevation of the extracellular calcium concentration causes a dramatic reduction of cell size, accompanied by a marked diminution of enzyme release and abolition of bone resorption. We propose that ionised calcium might play an important role in the local regulation of osteoclastic bone resorption.
Effects of taxol and nocodazole on insulin secretion from isolated rat islets of Langerhans
Authors: Howell S. L. , Hii C. S. , Shaikh S. , Tyhurst M.
Published: February 2005

Taxol, a promotor of microtubule polymerization, and nocodazole, which induces microtubule depolymerization, used at concentrations known to be specific for these effects in other cell types, were each shown to inhibit glucose-stimulated insulin secretion from isolated rat islets of Langerhans. These findings suggest that the dynamic regulation of microtubule polymerization-depolymerization in pancreatic B ceils may be important for insulin secretion via the microtubule-microfilamentous system.
Rat-liver fatty-acid-synthesizing complex
Authors: Gillevet P. M. , Dakshinamurti K.
Published: February 2005

Under conditions favoring lipogenesis, a high-molecular-weight species of acetyl-CoA carboxylase was isolated that did not co-sediment with the in vitro polymerized enzyme. Assays for ATP-citrate lyase, acetyl-CoA carboxylase, and fatty acid synthetase indicated that all three enzymes were associated together as a high-molecular-weight complex and that under low-lipogenic conditions the level of these enzymes decreased. Phosphorylation of the isolated complex shifted it toward a lower molecular weight.
Detection of TRH extended peptides in rat hypothalamus using an antibody raised to pGluHisProGlyLys
Authors: Cockle S. M. , Smyth D. G.
Published: February 2005

An antibody was raised to the synthetic pentapeptide pGluHisProGlyLys which, in radioimmunoassay (RIA), could detect the pentapeptide at a level of 10 fmole per tube and exhibited <0.5 per cent cross reactivity with a series of related peptides. The RIA was used to demonstrate the presence of C-terminally extended forms of thyrotropin releasing hormone (TRH) in rat hypothalamus. After extraction, the endogenous peptides were resolved by gel exclusion chromatography and TRH-extended peptides were revealed by trypsin digestion to release the pentapeptide. The TRH extended peptides occurred in substantial quantity, approximately 11 pmoles/g, indicating that only partial processing of the gene duplicated prohormone takes place.
Enzyme linked immunosorbent assay (ELISA) for the determination of protein-A
Authors: Considine P. J. , Duggan P. , Eadie A.
Published: February 2005

A competitive ELISA for the determination of protein-A concentration in culture supernatants is described. The sensitivity of the assay is 50 ng/ml and it may be used to determine concentrations of protein-A up to 1000 ng/ml. The assay is specific, rapid and suitable for routine screening of protein-A producing microorganisms.
Transcriptional induction of cellular gene expression during lytic infection with herpes simplex virus
Authors: Kemp L. M. , Brickell P. M. , La Thangue N. B. , Latchman D. S.
Published: February 2005

Herpes simplex virus Type 2 causes a severe repression of host cell biosynthesis at a number of levels. We show that despite this, non-viral cDNA clones derived from cellular RNA species which accumulate to high levels after infection can be isolated using differential screening techniques. By using nuclear run-off assays, we have shown that this RNA accumulation is mediated by transcriptional induction of the corresponding cellular genes.
Glucose-induced reduction of the sodium content in β-cell-rich pancreatic islets
Authors: Wesslén Nils , Bergsten Peter , Hellman Bo
Published: February 2005

The sodium contents of β-cell-rich pancreatic islets from ob/ob-mice were measured with an integrating flame photometer. After washing to an apparent steady state with different types of ice-cold media, islets incubated in the absence of glucose contained 79–108 mmol sodium kg−1 dry weight. Exposure to glucose resulted in 25 % reduction of the islet content of sodium. This effect became manifest in the presence of 5 mM glucose, there being no additional reduction with a further increase of glucose to 20 mM. Depression of Na+ activity may partially explain why glucose, under certain conditions, can lower cytoplasmic Ca2+ and even inhibit insulin release.
Species variations amongst proteinases in liver lysosomes
Authors: Béchet Daniel , Obled Alain , Deval Christiane
Published: February 2005

Cathepsin B, H, L and D activities in liver lysosomes were compared between species. Although cathepsin B and D were detected in bovine, pig, chicken and rat liver, striking species differences were evident for cathepsin H and L. Cathepsin L activity was particularly high in chicken lysosomal extracts, but could not be detected in bovine and pig extracts. Whereas there was no significant cathepsin H activity in bovine extracts, rat liver lysosomal extracts contained large amounts of cathepsin H activity.
The response of muscle protein synthesis to nutrient intake in postabsorptive rats: The role of insulin and amino acids
Authors: Preedy V. R. , Garlick P. J.
Published: February 2005

In 12 h fasted rats, rates of muscle protein synthesis were stimulated by refeeding for 1 h and by intragastric or intravenous infusion of an amino acid plus glucose mixture for 1 hr, but not by intravenous infusion of amino acids alone for 1 h. Intravenous injection of anti-insulin serum suppressed the response to feeding and to intragastric infusion, but not to intravenous infusion. It is concluded that the response of muscle protein synthesis to food intake is mediated by both insulin and amino acids acting in concert.
Dilatation of Golgi vesicles by monensin leads to enhanced accumulation of sugar nucleotides
Authors: Cecchelli Roméo , Cacan René , Porchet-Hennere Eliane , Verbert André
Published: February 2005

Incubation of mouse thymocytes with 10μM monensin for 1 hour induces morphological alterations characterized by the extensive dilatation and vacuolization of the Golgi complex. This effect is used to study the transport and utilization of labelled sugar nucleotides into intracellular vesicles by using thymocytes whose plasma membrane has been permeabilized by ammonium chloride treatment. It is demonstrated that monensin stimulates the incorporation of labelled sialyl, fucosyl, galactosyl, and N-acetylglucosaminyl residues. This enhanced incorporation is not due to a direct effect of monensin on glycosyltransferase activities themselves but is a consequence of a higher entry and accumulation of labelled sugar nucleotides in the dilated vesicles.
Modulation of membrane surface curvature by peptide-lipid interactions
Authors: Batenburg A. M. , de Kruijff B.
Published: February 2005

Recent reports on the interaction of cardiotoxin and melittin with phospholipid model membranes are reviewed and analyzed. These types of peptide toxins are able to modulate lipid surface curvature and polymorphism in a highly lipid-specific way. It is demonstrated that the remarkable variety of effects of melittin on the organization of different membrane phospholipids can be understood in a relatively simple model, based on the shape-structure concept of lipid polymorphism and taking into account the position of the peptide molecule with respect to the lipids. Based on the strong preference of the peptides for negatively charged lipids and the structural consequences thereof, and on preliminary studies of signal peptide-lipid interaction, a role of inverted or concave lipid structures in the process of protein translocation across membranes is suggested.
Isolation and native characterization of cysteine-rich collagens from bovine placental tissues and uterus and their relationship to types IV and V collagens
Authors: Abedin M. Z. , Ayad Shirley , Weiss Jacqueline B.
Published: February 2005

A simplified procedure for the fractionation and purification of different collagen types from various tissues is described which is particularly efficient in separating type-V from type-IV collagen, and highmol.-wt. (HMW) aggregates from 7 S collagen. Uterus and maternal villi contain 2 forms of type-V collagen −{α1(V)}2α2(V) and {α1(V)2α2(V)α3(V)}–which have been separated on DEAE-cellulose. Uterus however appears to be the richest source of both HMW aggregates and the {α1(V)2α2(V)α3(V)} collagen, and a probable relationship between these collagens is discussed.
The primary prostaglandin-inactivating enzyme of human placenta is a dimeric short-chain dehydrogenase
Authors: Mak Oi Tong , Jörnvall Hans , Jeffery Jonathan
Published: February 2005

The native form of NAD-dependent 15-hydroxyprostaglandin dehydrogenase of human placenta has a mol. wt. of about 50 0002 while the subunit tool. wt. is around 2g 0002 suggesting a dimeric quaternary structure. These propertie% the amino acid composition, insensitivity to EDTA, and inhibition patterns show general similarities to other short-chain dehydrogenases. Several hormones tested did not influence the activity of 15-hydroxyprostaglandin dehydrogenase2 but an unusual activation by two anti-depressant drugs was found and may relate to the existence of a natural regulatory factor.
Alpha1-antitrypsin: Structure, function and molecular biology of the gene
Authors: Kalsheker N.
Published: February 2005

Alpha1-antitrypsin (AAT) deficiency is one of the commonest inherited disorders in white Caucasians. This association has provided major insights into the pathogenesis of chronic lung disease. The three dimensional structure of the protein and the structure of the gene have been determined. Some of the signals required for regulation of expression and tissue-specificity have been defined. Genetic manipulation of active site residues may provide a new generation of biological compounds with potential therapeutic applications.
Biosynthesis of sulfated proteoglycans in amphibian embryonal cells
Authors: Løvtrup-Rein Huguette
Published: February 2005

The synthesis of sulfated proteoglycans in small explants from various parts of late blastulae from Ambystoma mexicanum or Xenopus laevis was investigated by incorporation of radioactive sulfate or glucosamine and galactosamine in media of low, normal or high tonicity. The explants differentiated into ciliated aggregates or fibroblast-like cells, or remained undifferentiated depending upon their origin in the embryo. High tonicity induces the explants to dissociated and prevents morphological differentiation, while low tonicity hardly affects this process. Yet, both types of media decrease the incorporation into glycosaminoglycans to various degrees, ranging from 40 to 80%, depending upon the species. In Xenopus, the uptake of sulfate is inhibited by as much as 90% in high tonicity media. The rate of incorporation of label is approximately twice as much in mesodermal as in animal or vegetal aggregates, which do not differ significantly. Animal aggregates from Ambystoma, however, revealed an exceptionally high uptake of sulfate. The relative distribution of chondroitin sulfates and heparan sulfates is not affected by changes in tonicity, except in Xenopus where high tonicity severely suppresses the synthesis of heparan sulfates, and is independent of the type of aggregate. The relationship between the synthesis of sulfated proteoglycans and processes involved in cell differentiation, especially cell adhesion, is discussed.
Effects of phenoxybenzamine on insulin secretion from isolated rat islets of Langerhans
Authors: Chan Susan L. F. , Morgan Noel G.
Published: February 2005

In isolated rat islets the α2-adrenergic antagonist phenoxybenzamine was found to be only partially effective at relieving the inhibition of glucose-induced insulin secretion mediated by noradrenaline. Further experiment revealed a direct inhibitory effects of phenoxybenzamine itself on the secretory response to glucose. At concentrations above 1 μM the antagonist inhibited insulin secretion in a dose-dependent manner, with greater than 50% inhibition at 50 μM. The inhibition of secretion developed rapidly in perifused islets, and was not altered when islets were also incubated with idazoxan or benextramine, suggesting that it did not reflect binding of phenoxybenzamine to the α2-receptor. Paradoxically phenoxybenzamine significantly increased the basal secretion rate in the presence of 4 mM glucose. The results demonstrate that phenoxybenzamine can exert direct effects on insulin secretion which are unrelated to its α-antagonist properties.
Regulation of hepatic cholesterogenesis by polar steroids accumulated after cholesterol feeding
Authors: Aguilera Juan A. , García-Molina Virginia , Arce Victor , García-Peregrín Eduardo
Published: February 2005

The incorporation of mevalonate into nonsaponifiable lipids by chick liver in vivo strongly increased between 1–18 days after hatching. Cholesterol feeding (2%) inhibited this. Synthesis of cholesterol was strongly inhibited, whereas the intermediates isolated by TLC accumulated. Most of the polar nonsaponifiable lipids that accumulated in liver 90 minutes after mevalonate administration to 18-day-old cholesterol-fed chicks were identified as lanosterol derivative. 3-Hydroxy-3-methylglutaryl-CoA reductase activity, as well as acetate and mevalonate incorporation into nonsaponifiable lipids, was inhibited by the presence of these compounds. To our knowledge, this is the first report of such inhibition; this confirms the physiological function of polar steroids in the regulation of cholesterogenesis in vivo.
A sensitive procedure for quantifying the phagocytic competence of blood granulocytes
Authors: Spangenberg P. , Crawford N.
Published: February 2005

The phagocytic activity of blood granulocytes can be quantitatively assayed by ingestion of opsonised paraffin oil droplets containing the dye “Oil Red-O” (Stossel, T. P., Mason, R. J., Hartwig, J., and Vaughan, M. (1972) J. Clin. Invest.51:615–624). We have modified this assay by incorporating [3H]glycerol into the oil droplets which allows a more sensitive and reproducible measurement of the phagocytic competence of blood granulocytes even at very low cell counts. Comparative studies after one day storage of the blood at 4°C is feasible since they retain 84 % of the phagocytic capacity measured when isolated from fresh blood.
The structure of a cDNA clone corresponding to mouse cardiac muscle actin mRNA
Authors: Leader David P. , Gall Irene , Campbell Paul C.
Published: February 2005

A cDNA library was constructed from mouse cardiac muscle mRNA, and a clone corresponding to part of the mRNA for the cardiac muscle isoform of actin was isolated from this library. The nucleotide sequence of the cloned insert was determined and was found to contain almost the complete amino acid coding region for actin (only codons for the first two amino acids, absent from the mature protein, were lacking) and a substantial portion derived from the 3′ untranslated region of the mRNA. Comparison of the latter with the corresponding region in cardiac actin mRNA from man and rat showed that this 3′ untranslated region has been subject to conservational pressure during evolution. However a comparison with the corresponding region in skeletal muscle actin mRNAs indicated that the pattern of conservation is quite different in the two striated muscle actin isoforms.
Chromatin structure of genes during the cell cycle
Authors: Jing-de Zhu , Paul John
Published: February 2005

K562 ceils were separated by centrifugal elutriation into 5 fractions each of which had a unique distribution of ceils at different phases of the cell cycle. A study of DNAseI sensitivity of the e- and γ-globin genes, which are expressed in these cells, and the λ light chain immunoglobulin gene, which is not expressed, in nuclei from each of the 5 fractions was undertaken. There was no detectable difference in the arrangement of DNAseI-hypersensitive sites (DHS) in chromatin of each of the three genes in the different fractions.
Angiotensin as a model for hormone – receptor interactions
Authors: Moore Graham J. , Matsoukas John M.
Published: February 2005

Proton magnetic resonance and chemical reactivity studies have demonstrated the presence of a tyrosine charge relay system in angiotensin which is analogous to the serine charge relay system present at the active site of serine proteases. Receptor activation by angiotensin can be explained by electronic effects deriving from an interaction of the charge relay system with stacking of the histidine and phenylalanine rings. Experiments with serine protease inhibitors suggest the possibility that mechanistic features of the interaction of angiotensin with its receptors may apply to other ‘phenoxyl’ hormones including certain peptides, steroids and catecholamines.
Effect of bilateral adrenalectomy on VIP receptor/effector system in rat intestinal epithelial cells
Authors: Fernández-Moreno M. D. , Carrero I. , Arilla E. , Prieto J. C.
Published: February 2005

The number of vasoactive intestinal peptide (VIP) receptors and the efficiency of VIP in the stimulation of cyclic AMP accumulation in rat jejunal epithelial cells increased after bilateral adrenalectomy. However, this condition increased neither receptor affinity nor VIP potency. In addition, jejunal VIP levels followed a parallel increase. These changes reversed to control conditions after glucocorticoid replacement with dexamethasone indicating that adrenalectomy modifies the intestinal VIP receptor/effector system and suggest a relationship between corticosteroids and VIP in the functions of intestinal epithelium.
Diabetes is not associated with a change in the elemental composition of the pancreatic B cell in diabetic C57BL KsJ-db/db mice
Authors: Juntti-Berggren Lisa , Lindh Ulf , Berggren Per-Olof , Berglund Ove , Frankel Barbara J.
Published: February 2005

Freeze-dried pancreas sections from 7-, 17-and 27-week-old genetically diabetic (db/db) and normal (±/±) mice were subjected to proton bombardment and the concentrations of 15 elements in B cells and exocrine pancreas were calculated from the characteristic X-rays emitted. In the 7-week-old diabetic animals, B cells contained significantly above-normal levels of Na and S, while exocrine pancreas contained subnormal levels of Ca, and excess Mn. The B cells from the 17-week-old diabetic animals contained subnormal levels of Cu and the exocrine pancreas of the 27-week-old diabetic animals was deficient in Cd. The 7-, 17- and 27-week-old, genetically diabetic (db/db) mice were hyperglycemic, hyperinsulinemic and heavier than age-matched normal (±/±) mice. Although significant changes were found in elemental composition when comparing both B cells and exocrine pancreas at different ages, the changes were not consistent. Therefore, it appears as if the measured elemental changes were random and not related to the onset of diabetes.
Mechanism of cystine reaccumulation by cystinotic fibroblasts in vitro
Authors: Forster Susan , Scarlett Lynne , Lloyd John B.
Published: February 2005

It is well established that when cystine-depleted cystinotic cells are cultured in cystine-containing medium, they reaccumulate cystine within their lysosomes more rapidly than when cultured in cystine-free medium. This has been a puzzling result, since the lysosome membrane of cystinotic cells is impermeable to cystine. To probe the mechanism of cystine reaccumulation, we have measured reaccumulation in the presence of colchicine, an inhibitor of pinocytosis, or of glutamate, a competitive inhibitor of cystine transport into human fibroblasts. Colchicine had no effect, thus eliminating pinocytosis as a putative mechanism for cystine translocation from the culture medium to the lysosomes. Glutamate, however, strongly inhibited cystine reaccumulation. It is concluded that the true mechanism is as follows. 1. Exogenous cystine crosses the plasma membrane on the cystine-glutamate porter. 2. Cystine is reduced in the cytoplasm by GSH. 3. The cysteine that is generated enters the lysosome, where it becomes cystine by participating in the reduction of cystine residues during intralysosomal proteolysis, or by autoxidation.
“Calcium receptors” on eukaryotic cells with special reference to the osteoclast
Authors: Zaidi Mone
Published: February 2005

There is a growing list of cells that are capable of detecting and responding to changes in the concentration of extracellular calcium. The two classic examples of this behaviour are the calcitonin-secreting parafollicular cells of the thyroid and parathyroid hormone-secreting chief cells of the parathyroid gland. A more recent addition to this list is the renin-secreting juxtaglomerular cell of the kidney. Particularly intriguing has been independently the discovery by two laboratories, that the resorptive cell of bone, the osteoclast, is capable of detecting changes in ambient calcium. A common theme amongst all these so called “calcium-responsive” cells is that extracellular calcium increases elevate intracellular calcium levels, and this intracellular signal is either stimulatory or inhibitory to the functional response. But how these cells detect changes in the concentration of extracellular calcium, and how these recognition events are subsequently transformed into intracellular signals that regulate cell function are somewhat less clear. The commentary reveals some recent developments that seemingly provide insights into these mechanisms, with special reference to the osteoclast.
“In vivo” amplification of biological activity of tetragastrin by amino acid hydroxamates
Authors: Bali J. P. , Mattras H. , Previero A. , Coletti-Previero M. A.
Published: February 2005

Rat blood was shown to contain an aminopeptidase which rapidly hydrolyses short peptides containing an aromatic amino acid as N-terminal residue. Using tetragastrin (Trp-Met-Asp-PheNH 2) as substrate, we showed that some amino acid hydroxamates inhibit rat aminopeptidase activity ‘in vitro’ in the following order: HTrpNHOH > HPheNHOH ≫ HAIaNHOH. The same hydroxamates markedly enhanced the biological activity of tetragastrin ‘in vivo’. The amplification of the secretory effect, correlated with the amount of the hydroxamate used, strongly suggests that these compounds can stabilize a number of active peptides in vivo by inhibiting their proteolytic degradation.
Activation of the cAMP-generating system by vasoactive intestinal polypeptide (VIP) in the human laryngeal malignant cell line HEp-2
Authors: Prost Annie , Emami Shahin , Rosselin Gabriel , Gespach Christian
Published: February 2005

In the presence of 3-isobutyi-l-methylxanthine, VIP produced a dose-related (3 × 10−9 − 10−7 M) increase (g-fold) in cAMP production in isolated HEp-2 cells incubated at 15°C in KRP buffer. Among the peptides structurally related to VIP, including secretin (10−7 M), pancreatic glucagon (10−6 M), PHI, somatostatin-14 (10−6 M), hpGRF (10−8 − 4 × 10−M), GIP (2 × 10−7 M), only PHI (3 × 10−7 M and above) is able to activate the cAMP-generating system in HEp-2 cells, but at 102 times lower potency. Under the same conditions, histamine (10−3 M) was also ineffective, while PGE 2 (10−7 − 10−4 M) increased (0-fold) basal cAMP levels in HEp-2 cells. The VIP effect is related to the interaction os the peptide on VIP recognition sites (12SI-VIP-binding capacity), coupled to the membrane-bound adenylate cyclase. The results indicate that the transformed laryngeal cell line HEp-2 possessesa receptor-cAMP system preferentially activated by VIP (relative potencies: VIP > PHI ≫ other peptides of the secretin family), and suggest that this neuropeptide could modulate biological functions in normal laryngeal epithelia in man.
Immunocytochemical localization on β-hexosaminidase and electron-microscopic characterization of human fibroblasts following treatment with monensin and nigericin
Authors: Vladutiu Georgirene D.
Published: February 2005

Immunocytochemical localization of 8-hexosaminidase in cultured human skin fibroblasts was performed in the presence or absence of the Na+/K+ ionophores monensin and nigericin. In the presence of monensin, β-hexosaminidase accumulated in the periphery of swollen vesicles in the paranuclear region of fibroblasts from normaI individuals and from patients with mucolipidosis II. Nigericin-treated cells had more extensive vacuolization of the cytoplasm and the localization of the enzyme was more diffuse within these vacuoles. Morphological studies at the ultrastructral level indicated that a perturbation of the Golgi region occurred during ionophore treatment. These findings suggest that β-hexosaminidase in ionophore-treated fibroblasts is trapped in a time- and dose-dependent manner in the paranuclear region presumed to be the swollen cisternae of the Golgi region, or adjacent vesicles derived from the Golgi region. Furthermore, fibrobiasts are more sensitive to perturbation by nigericin than by monensin at similar concentrations and exposure times. These data support biochemical findings that the two ionophores differentially inhibit the transport of lysosomal enzymes in the Golgi region.
Dissimilar effects of L and D amino acids on the growth of Tetrahymena
Authors: Darvas Zsuzsa , Nozawa Y. , Csaba G.
Published: February 2005

Of the L and D configurations of four amino acids (phenylalanine, valine, tryptophan, tyrosine) tested for influence on the growth rate of Tetrahymena, only L-tyrosine was able to induce imprinting in Tetrahymena pyriformis Zeuthen. D-valine stimulated the division of T.pyriformis NT-1, but failed to induce imprinting. The experiments have substantiated the selectivity of the amino acid receptors of Y.pyriformis, and the extraordinary imprinting potential of tyrosine as well, as judged by its influence on the growth rate.
Changes in thermogenesis and brown fat activity in response to tumour necrosis factor in the rat
Authors: Coombes R. C. , Rothwell N. J. , Shah P. , Stock M. J.
Published: February 2005

A single intravenous injection of recombinant human tumour necrosis factor (TNF) resulted in significant, but transient (24–48 hr) reductions in food intake and body weight, and increases in rectal temperature, resting oxygen consumption (VO2) and brown adipose tissue (BAT) thermogenic activity (mitochondrial GDP-binding). The increased VO2 was inhibited by β-adrenergic blockade (propranolol), and activation of BAT was prevented by denervation of the tissue. In adult (4-month old) animals, TNF induced greater reductions in food intake and body weight, caused general malaise and some fatalities, but did not significantly alter VO2 or BAT activity. However, the reduction in VO2 following β-adrenergic blockade was greater in TNF-treated rats and BAT activity was enhanced when compared to pair-fed controls. Injection of adult rats with gamma-interferon induced small changes in body weight and temperature which were slightly potentiated when injected with a low dose of TNF. The results indicate that TNF stimulates sympathetic outflow to BAT. This effect may be partly responsible for the increases in body temperature and metabolic rate associated with TNF treatment and with cancer cachexia.
Endopeptidases and prohormone processing
Authors: Darby N. J. , Smyth D. G.
Published: February 2005

Peptide hormones and peptide transmitters are generated from polypeptide precursors by specific cleavage reactions which take place principally at sites formed by single or paired basic residues. Not all the possible cleavage sites are utilised, however, and the degree of processing of many propeptides has been found to vary according to the tissue of origin. The restricted nature of processing reactions could point to the existence of a series of enzymes with stringent specificities, recognising regions of structure in addition to the single or paired basic residues. Alternatively the action of processing enzymes may be directed by conformation of the pro-peptide which could focus the action of a protease onto or away from a particular site. In addition certain post-translational modifications such as glycosylation or phosphorylation may influence the accessibility of a site to the approach of a processing enzyme. In this review we describe recent advances that have been made in the characteristisation of proteolytic processing enzymes, we examine the relevance of the various factors that could account for restricted processing and discuss new approaches that may lead to better understanding of the mechanisms involved.
Carbohydrate recognition systems in avian sinusoidal liver cells
Authors: Dini Luciana , Mattioli Palma
Published: February 2005

We studied the carbohydrate recognition systems on liver sinusoidal cells of adult chicken and 20-day-old embryos. We localized and quantified the binding sites for glycoproteins exposing terminal N-acetylglucosamine (GlcNAc), mannose and galactose (Gal) residues. Sinusoidal liver cells from animals of both ages express on their cell surfaces binding sites for GlcNAc, mannose and galactose residues, while hepatocytes bind glycoproteins with GlcNAc resiudes. The gold particles distribution on Kuffer cells depend on the binding sites and the age considered. Binding sites for GlcNAc and Gal residues are generally present as clusters of gold granules, while mannose-specific binding sites are always as single gold granules. Ligand-gold complexes bound on endothelial cells are always present on the coated regions of the cell surface. The number of GlcNAc and Gal-specific receptors expressed on the cell surface of Kupffer cells undergoes modifications between embryonal and adult life.
GTPγS-induced calcium transients and exocytosis in human neutrophils
Authors: Nüße Oliver , Lindau Manfred
Published: February 2005

Exocytosis and intracellular free calcium ([Ca2+]in) were simultaneously recorded in single human neutrophils using patch-clamp capacitance measurements and the fura-2 fluorescence ratio method. Intracellular application of guanosine-5′-O(3-thiotriphosphate) (GTPγS) stimulates both exocytosis and a calcium transient. The calcium transient starts to develop after a lag phase of ∼40s and normally appears to trigger the onset of exocytosis indicated by the beginning of the capacitance increase. After this delay [Ca2+]in increases from ∼150 nM to ∼600 nM with a sigmoidal time course. The peak concentration is reached within ∼30 s but the main increase occurs during ∼ 3s. [Ca2+]in subsequently decays within 1–2 min to a level which is close to the resting value. This calcium transient is due to calcium release from inositoltrisphosphate-sensitive intracellular stores. Exocytosis also occurs if the calcium transient is abolished by intracellular EGTA but the lag phase is markedly prolonged. The GTPγS-induced calcium transient is very similar to that observed after stimulation with N-formyl-methionyl-leucyl-phenylalanine. The interplay between guanine nucleotides, [Ca2+]in and exocytosis in neutrophils closely resembles previous results obtained in mast cells suggesting a similar regulation of exocytosis in both cell types.
In vitro and in vivo effect of chloropromazine, imipramine and lithium chloride on monoamine oxidase activity in rat brain mitochondria
Authors: Nag Maitreyi , Nandi Namita
Published: February 2005

Chloropromazine (CPZ) and imipramine at a concentration of 1×10−3 M inhibit rat brain mitochondrial monoamine oxidase activity in vitro by 70 and 55% respectively, while lithium, even at a concentration of 0.05 M, inhibits the activity of this enzyme very negligibly (4%). In vivo, these drugs at a dose level of 56 mg CPZ, 76 mg Jimipramine and 76 mg lithium chloride/Kg body wt., did not cause any observable variation from normal in brain mitochondrial monoamine oxidase activity.
Interaction of diphtheria toxin fragment A and of elongation factor 2 with Cibacron blue
Authors: Rambelli Fioretta , Brigotti Maurizio , Sperti Simonetta , Montanaro Lucio
Published: February 2005

Diphtheria toxin fragment A interacts with Cibacron blue in solution, although it is not retained by blue Sepharose columns. Difference spectral titration of fragment A with the dye gives a dissociation constant of the order of 10−5 M and a 1:1 stoichiometry for the complex. In equilibrium dialysis experiments Cibacron blue behaves as a competitive inhibitor of the binding of NAD to diphtheria toxin fragment A. The dye inhibits in a non-competitive way the fragment A-catalysed transfer of ADP-ribose from NAD to elongation factor 2 (EF2). By affinity chromatography on blue Sepharose a binding of EF2 and of ADP-ribosyl-EF2 with the dye is also demonstrated. GDP, GTP and GDP(CH2)P are able to displace EF2 from blue Sepharose.
Glucagon treatment of rats inhibits the accumulation of lysophospholipids by liver mitochondria during preparation and subsequent incubation
Authors: Armston Annie E. , Halestrap Andrew P.
Published: February 2005

1) Rat liver mitochondria isolated from rats exposed to32Pi for 24 h and treated with glucagon for 15 min before sacrifice contained less lysophosphatidylcholine and lysophosphatidylethanolamine than those from control animals. 2) Incubation of the mitochondria at 37°C for 15 min increased the lysophosphatidylcholine concentration of control mitochondria but not of those from glucagon-treated animals. 3) Lysophosphatidylethanolamine showed little change during in vitro incubation of mitochondria and this was not affected by glucagon treatment. 4) These results are discussed in relation to the effects of glucagon treatment on mitochondrial function in situ and in vitro.
Preparation of a cell-free translation system from a wild-type strain of Neurospora crassa and translation of pyruvate kinase messenger RNA
Authors: Devchand M. , Kapoor M.
Published: February 2005

A cell-free in vitro translation system exhibiting high activity has been developed from wild-type Neurospora crassa mycelium. The isolation is simple and fast, and the homogenization does not appear to affect the activity of mycelial proteases and nucleases. This system is capable of supporting efficient translation of exogenously added homologous RNA as demonstrated by the experiments with PK-specific mRNA. In addition, it translates heterologous RNA efficiently, shown by the translation of globin mRNA. We did not examine the Neurospora lysate for post-translational modification activity. The procedure used for the preparation of Neurospora cell-free extracts should be readily applicable to the other filamentous fungi.
Factors affecting the metabolic control of cytosolic and lysosomal glycogen levels in the liver
Authors: Geddes Robert , Taylor Jacqueline A.
Published: February 2005

Rats with a gentic deficiency of phosphorylase kinase have been treated with the 1,4-α-glucosidase inhibitor, Acarbose. Lysosomal glycogen metabolism has been markedly altered and the results support the concept of a feedback control mechanism operating on the uptake mechanism into the lysosomal compartment.