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PubMed2003

The binding of beta- and gamma-cyclodextrins to glycogen phosphorylase b: kinetic and crystallographic studies.

A number of regulatory binding sites of glycogen phosphorylase (GP), such as the catalytic, the inhibitor, and the new allosteric sites are currently under investigation as targets for inhibition of hepatic glycogenolysis under high glucose concentrations; in some cases specific inhibitors are under evaluation in human clinical trials for therapeutic intervention in type 2 diabetes. In an attempt to investigate whether the storage site can be exploited as target for modulating hepatic glucose production, alpha-, beta-, and gamma-cyclodextrins were identified as moderate mixed-type competitive inhibitors of GPb (with respect to glycogen) with K(i) values of 47.1, 14.1, and 7.4 mM, respectively. To elucidate the structural basis of inhibition, we determined the structure of GPb complexed with beta- and gamma-cyclodextrins at 1.94 A and 2.3 A resolution, respectively. The structures of the two complexes reveal that the inhibitors can be accommodated in the glycogen storage site of T-state GPb with very little change of the tertiary structure and provide a basis for understanding their potency and subsite specificity. Structural comparisons of the two complexes with GPb in complex with either maltopentaose (G5) or maltoheptaose (G7) show that beta- and gamma-cyclodextrins bind in a mode analogous to the G5 and G7 binding with only some differences imposed by their cyclic conformations. It appears that the binding energy for stabilization of enzyme complexes derives from hydrogen bonding and van der Waals contacts to protein residues. The binding of alpha-cyclodextrin and octakis (2,3,6-tri-O-methyl)-gamma-cyclodextrin was also investigated, but none of them was bound in the crystal; moreover, the latter did not inhibit the phosphorylase reaction.

Animals↗
PubMed1983

Cooperative immunoassays: ultrasensitive assays with mixed monoclonal antibodies.

Mixtures of certain monoclonal antibodies appear to bind human chorionic gonadotropin in a "cooperative" fashion because they form circular complexes with the hormone. Experiments illustrate how this property might be exploited to develop very sensitive immunoassays for human chorionic gonadotropin or any other antigen. Since the assays are not based on competitive inhibition between radiolabeled and unlabeled antigen, they are much more sensitive than a traditional radioimmunoassay in which either one of the same antibodies is used alone.

Antibodies, Monoclonal↗
PubMedDate not supplied

What's wrong with strategy?

Why is it that successful strategies are rarely developed as a result of formal planning processes? What is wrong with the way most companies go about developing strategy? Andrew Campbell and Marcus Alexander take a common sense look at why the planning frameworks managers use so often yield disappointing results. Companies often fail to distinguish between purpose (what an organization exists to do) and constraints (what an organization must do in order to survive), the authors say. Many executives mistakenly believe, for example, that satisfying stakeholders is an objective that drives thinking about strategy. In fact, it's a constraint, not an objective. Companies that don't win the loyalty of stakeholders will go out of business. Strategy is not about plans but about insights, the authors add. Strategy development is the process of discovering and understanding insights and should not be confused with planning, which is about turning insights into action. Furthermore, because executives develop most of their insights while actually doing the real work of running a business, it is important for companies not to separate strategy development from implementation. Is there a better way? The answer is not new planning processes or more effort. Instead, managers must understand two fundamental points: the benefit of having a well-articulated, stable purpose and the importance of discovering, understanding, documenting, and exploiting insights about how to create value.

Commerce↗
PubMed1985

Solid-phase enzyme-receptor assay (SPERA): a competitive-binding assay for glycopeptide antibiotics of the vancomycin class.

A solid-phase enzyme-receptor assay (SPERA) has been developed for glycopeptide antibiotics of the vancomycin class such as teicoplanin, vancomycin, ristocetin, avoparcin, actaplanin, A-47934, A-41030, and A-35512-B. The assay exploits the mechanism of most action of these antibiotics, which is based on their interaction with acyl-D-alanyl-D-alanine, a constituent of the walls of most growing bacterial cells. The antibiotics and enzyme-labeled teicoplanin compete for a synthetic analog of the biological receptor, albumin-epsilon-aminocaproyl-D-alanyl-D-alanine. The various antibiotics produced different competition curves, 50% displacement being obtained with antibiotic concentrations ranging from 0.04 to 4 mg/L, vancomycin and actaplanin being the weakest and strongest competitors, respectively. For teicoplanin in human serum the intra-assay CV was 7.2%, the interassay CV was 11.2%, and the analytical recovery 94%. Teicoplanin concentrations obtained by SPERA (chi) correlated well with those obtained by microbiological assay (y): y = 1.03 chi + 0.053 (r = 0.943; n = 60). We conclude that SPERA is a powerful tool for identification and quantitative detection of glycopeptide antibiotics, even in complex media.

Anti-Bacterial Agents↗
PubMed2004

Structures of the Escherichia coli PutA proline dehydrogenase domain in complex with competitive inhibitors.

Proline dehydrogenase (PRODH) catalyzes the first step of proline catabolism, the flavin-dependent oxidation of proline to Delta(1)-pyrroline-5-carboxylate. Here we present a structure-based study of the PRODH active site of the multifunctional Escherichia coli proline utilization A (PutA) protein using X-ray crystallography, enzyme kinetic measurements, and site-directed mutagenesis. Structures of the PutA PRODH domain complexed with competitive inhibitors acetate (K(i) = 30 mM), L-lactate (K(i) = 1 mM), and L-tetrahydro-2-furoic acid (L-THFA, K(i) = 0.2 mM) have been determined to high-resolution limits of 2.1-2.0 A. The discovery of acetate as a competitive inhibitor suggests that the carboxyl is the minimum functional group recognized by the active site, and the structures show how the enzyme exploits hydrogen-bonding and nonpolar interactions to optimize affinity for the substrate. The PRODH/L-THFA complex is the first structure of PRODH with a five-membered ring proline analogue bound in the active site and thus provides new insights into substrate recognition and the catalytic mechanism. The ring of L-THFA is nearly parallel to the middle ring of the FAD isoalloxazine, with the inhibitor C5 atom 3.3 A from the FAD N5. This geometry suggests direct hydride transfer as a plausible mechanism. Mutation of conserved active site residue Leu432 to Pro caused a 5-fold decrease in k(cat) and a severe loss in thermostability. These changes are consistent with the location of Leu432 in the hydrophobic core near residues that directly contact FAD. Our results suggest that the molecular basis for increased plasma proline levels in schizophrenic subjects carrying the missense mutation L441P is due to decreased stability of human PRODH2.

Bacterial Proteins↗
PubMed2004

Genomics in environmental health research--opportunities and challenges.

Environmental health research impacts both environmental health regulatory policy and the practice of medicine. However, this area of medical research has not garnered public support and attention of medical researchers because of its emphasis on prevention and public health. Also, the pervasiveness of a scientific culture wedded to old problems and outdated technologies and models systems has not been helpful in generating enthusiasm for the field. While the emphasis on prevention is both laudable and appropriate, the adoption of cutting-edge technologies to exploit the new scientific opportunities, made possible by the nation's investment in genomics, is essential if the discipline expects to be competitive with other highly deserving programs. The new 'omics' era of environmental health research, ushered in over the past decade, characterized by the linkage of genomics, proteomics and metabolomics to conventional toxicology and pathology databases, holds great promise for elucidating mechanisms of gene-environment interaction in human health and disease. These combined approaches will allow one to monitor multiple molecular events, pathways and interactive networks simultaneously-a requirement for elucidating toxic mechanisms. But, before embracing the 'omics' technologies as the 'be all-end all;' they need to be validated for their predictive capacities in large-scale multi-institutional studies, such as those described in this article.

Animals↗
PubMed2004

Some drugs more equal than others: pseudo-generics and commercial practice.

This article analyses the impact of the Department of Health and Ageing's brand price premium policy for some products listed on the Pharmaceutical Benefits Scheme. The policy, introduced in 1990, allows pharmaceutical companies to charge patients an out-of-pocket expense for post-patent brands of pharmaceuticals. One of the policy's intended goals was to increase consumer awareness of price differentials between competing brands, with a view to encouraging greater use of cheaper generic products. More than fourteen years since its introduction, it is debatable whether the policy has achieved this aim. This article looks at how the brand price premium policy can be exploited by global pharmaceutical giants to entrench big-name brands in the Australian pharmaceutical market and, in some cases, prevent 'true' competition from generic pharmaceuticals. This is being done through the establishment of 'pseudo-generics' that are sourced from the same factory floor as the original product.

Australia↗
PubMed1997

The myth of managed care. Moving beyond managing costs to really managing care.

Today's managed care manages costs, not care. Care is lopsided with costly physician and provider control of the information, decision-making and treatment processes that are built on outdated fee-for-service incentives. Fast moving providers who exploit opportunities to redesign care, shifting more responsibility and control to non-physician providers and to patients will gain a major competitive advantage. These providers are much more likely to stand out from their peers, enabling them to attract patients and contracts.

Costs and Cost Analysis↗
PubMed1978

Binding interactions of glycoproteins with lectins.

Since plant lectins were used to help define differences between normal and transformed cell surfaces (reviewed in References 1-4), they have been employed in many other situations where their sugar-recognition specificities could be used to advantage. One of these applications has been the purification and characterization of enzymes and other proteins; this work is reviewed here in order to define some of the variables that affect binding of glycoproteins to lectins, as well as to demonstrate how this technique has been profitably exploited for isolation of purified glycoproteins, and for their better understanding.

Binding, Competitive↗
PubMed2002

Invasion of vacant niches and subsequent sympatric speciation.

An individual-based simulation study was conducted to examine the population dynamics of 'invasion of a vacant niche' and subsequent speciation (by reproductive isolation) when food resources are randomly distributed spatially within the habitat and the frequencies of different food types are bimodally distributed (i.e. smaller and larger sizes of food being most abundant). The initially vacant niche was that of unused larger sizes of food. When phenotypic variation for resource use (i.e. food sizes) was small in the initial population, and each female could choose a mate from anywhere in the habitat, the population could not invade the vacant niche. But when the dispersal distance of the offspring and the area within which a female could choose a mate were small (i.e. the genetic neighbourhood size was small), the population could, in most cases, evolve to use both smaller and larger food sizes and form sister species sympatrically, with each species utilizing one of the two niches (small and large sizes of food). When phenotypic variation in resource use in the initial population was large, the population could, in most cases, invade the vacant niche by evolving to use both smaller and larger sizes of food. The probability of speciation increased as the dispersal distance of offspring decreased. The results indicate that populations whose individuals have small Wright's genetic neighbourhoods may often exploit a vacant niche and diversify sympatrically in the process.

Animals↗
PubMed2004

The evolving science of quality measurement for hospitals: implications for studies of competition and consolidation.

The literature on hospital competition and quality is young; most empirical studies have focused on few conditions and outcomes. Measures of in-hospital mortality and complications are susceptible to bias from unmeasured severity and transfer/discharge practices. Only one research team has evaluated related process and outcome measures, and none has exploited chart-review or patient survey-based data. Prior studies have generated inconsistent findings, suggesting the need for additional research. We describe the strengths and limitations of various approaches to quality measurement, summarize how quality has been operationalized in studies of hospital competition, outline three mechanisms by which competition may affect hospital quality, and propose measures appropriate for testing each mechanism.

Economic Competition↗
PubMed2001

Costs of intraspecific and interspecific host sharing in acanthocephalan cystacanths.

Larval helminths often share individual intermediate hosts with other larval worms of the same or different species. In the case of immature acanthocephalans capable of altering the phenotype of their intermediate hosts, the benefits or costs of host sharing can be evaluated in terms of increased or decreased probability of transmission to a suitable definitive host. Competitive interactions among the immature stages of acanthocephalans within the intermediate host could create additional costs of host sharing, however. The effects of intraspecific and interspecific interactions were measured in 3 sympatric species of acanthocephalans exploiting a population of the amphipod Echinogammarus stammeri in the River Brenta, Italy. The strength of interactions was assessed from differences in the size achieved by infective cystacanths in the intermediate host. The size of Pomphorhynchus laevis cystacanths was not correlated with host size, whereas the size of Acanthocephallus clavula and Polymorphus minutus cystacanths increased with host size. Reductions in cystacanth size caused by intraspecific competition were only detected in P. laevis, but may also occur in both A. clavula and P. minutus. When co-occurring in the same amphipod with cystacanths of A. clavula, cystacanths of P. laevis attained a smaller size than when they occurred on their own. This effect was not reciprocal, with the size of A. clavula cystacanths not being affected. This supports earlier suggestions that it is adaptive for A. clavula to associate with P. laevis in amphipod intermediate hosts, with both species going to the same fish definitive hosts. In contrast, cystacanths of P. laevis achieved their largest size when they co-occurred in an amphipod with a cystacanth of P. minutus, which has a different definitive host (i.e. birds). These findings suggest that the net benefits of sharing an intermediate host can only be estimated by taking into account both the effects on transmission success and the consequences for cystacanth development.

Acanthocephala↗
PubMed2000

Competition and dental services.

Dental services for adults are different from all other Norwegian health services in that they are provided by private producers (dentists) who have full freedom to establish a practice. They have had this freedom since the end of World War II. A further liberalization of the market for dental services occurred in November 1995, when the so-called normal tariff was repealed. The system changed from a fixed fee system to a deregulated fee system. In principle, the market for dental services for adults operates as a free competitive market, in which dentists must compete for a market share. The aim of this study was to study the short-term effects of competition. A comprehensive set of data on fees, practice characteristics, treatment profiles and factors that dentists take into account when determining fees was analysed. The main finding was that competition has a weak effect. No support was found for the theory that the level of fees is the result of monopolistic competition or monopoly. The results also provided some evidence against the inducement hypothesis. At this stage, it is interesting to notice that dentists do not seem to exploit the power they have to control the market. One explanation, which is consistent with the more recent literature, is that physicians' behaviour to a large extent is influenced by professional norms and caring concerns about their patients. Financial incentives are important, but these incentives are constrained by norms other than self-interest. The interpretation of the results should also take into account that the deregulation has operated for a short time and that dentists and patients may not yet have adjusted to changes in the characteristics of the market.

Adult↗
PubMed1993

Synthesis and applications of phosphonoacetic derivatives.

In this paper, the synthesis of new phosphonoacetic acid derivatives and their applications in fields of biotechnological interest are discussed. Phosphonoacetic acids are competitive inhibitors of alkaline phosphatase, an enzyme widely used in diagnostics, as colorimetric detection tool. The phosphonoacetic acid's inhibition activity has been exploited by us for the obtainment of an innovative technique for non-radioactive DNA probes detection, the last being based on DNA labeling with the enzyme inhibitor, followed by detection by means of the chromogenic enzyme and substrate. Moreover, we have found a further application of phosphonoacetic acids, by the preparation of an affinity chromatography support that has been revealed to be very effective in the purification of alkaline phosphatase. Finally, phosphonoacetic acid derivatives have been tested also for their antiviral activity. Some of them, examined in preliminary in vitro experiments, have been found very active against Herpes simplex virus.

Antiviral Agents↗
PubMed1992

Anthroylcholine bromide: a fluorescent ligand for the muscarinic receptor.

The action of anthroylcholine bromide, a new fluorescent probe, has been studied at the cellular (contraction of intestinal muscle) and subcellular levels (binding of 3H-quinuclidinyl benzilate to brain cortex membranes, fluorescence and enzyme activity) with the following results: 1. Anthroylcholine bromide competitively antagonized the contractile effect of acetylcholine in isolated rat duodenum (pA2 = 6.12), but had no effect either on the concentration response curves to histamine or to noradrenaline in isolated guinea pig ileum and rat vas deferens. 2. Anthroylcholine bromide displaced competitively 3H-quinuclidinyl benzilate from brain cortex membranes (Ki = 0.77 mumol/l). 3. Direct binding to the muscarinic site could be measured by exploiting the fluorescence properties of the probe. Binding displaceable by atropine (approximately 20% change in fluorescence) had an apparent affinity constant similar to that found with indirect methods. In contrast, d-tubocurarine did not displace the probe from its site, and atropine- or d-tubocurarine-sensitive binding of anthroylcholine bromide to Torpedo marmorata electric organ membranes, rich in nicotinic receptors, was not observed. These properties suggest the applicability of the probe to study the distribution, structure and/or kinetic properties of the muscarinic receptor.

Acetylcholine↗
PubMed1999

Combination of vaccination and competitive exclusion to prevent Salmonella colonization in chickens: experimental studies.

Vaccination and competitive exclusion (CE) represent accepted prophylactic measures to control Salmonella infections in chickens. To use the advantages of both the CE technique and vaccination with live Salmonella vaccines the combination of these methods was studied. In three experiments, SPF chickens were pre-treated using combined or unique administration of CE and vaccination with a live Salmonella typhimurium strain on days 1 and 2 of life and challenged with the antibiotic resistant, but otherwise isogenic mutant of this Salmonella typhimurium strain on days 3, 15 or 40 of life. The caecal colonization of both the vaccine and the challenge strain and the antibody response after infection were examined to evaluate the protective effects of the different combinations. The exclusion effect of CE cultures against Salmonella infection could be seen in very young chicks and was still considerable on day 40 of life of the birds. The Salmonella wild-type strain used as vaccine alone also resulted in a substantial protective effect against homologous challenge. The combined administration of competitive exclusion and immunization using the Salmonella wild-type strain as vaccine resulted in a considerable additional protective effect above the level of the respective exclusive application of these prophylactic measures. Administration of the Salmonella vaccine strain prior to or simultaneously with the CE culture produced the best protective effect, because such combinations ensure an adequate persistence of the vaccine strain as prerequisite for the expression of colonization inhibition effects and a strong immune response. The full exploitation of this potential using attenuated live Salmonella vaccines will require the presence of high inhibitory and immunogenic properties in the vaccine strain after attenuation of a selected parent strain. The combination of competitive exclusion and vaccination as a new measure in integrated control programmes against Salmonella infection in poultry could result in a considerable increase of protection in both very young and older chickens.

Animals↗
PubMed2005

Nutrient-limited food webs with up to three trophic levels: feasibility, stability, assembly rules, and effects of nutrient enrichment.

Community structure is controlled, among multiple factors, by competition and predation. Using the R* rule and graphical analysis, we analyse here the feasibility, stability and assembly rules of resource-based food webs with up to three trophic levels. In particular, we show that (1) the stability of a food web with two plants and two generalist herbivores does not require that plants' resource exploitation abilities trade-off with resistance to the two herbivores, and (2) food webs with two plants and either one generalist herbivore and a carnivore or two generalist herbivores and two generalist carnivores are not feasible because of cascade competition between top consumers. The relative strength of species interactions and the relative impacts of plants and herbivores on factors which control their growth also play a critical role. We discuss how community structure constrains assembly rules and yields cascades of extinctions in food webs.

Animals↗
PubMed2006

Molecular diversity and evolution of the Siglec family of cell-surface lectins.

Sialic acids are a family of acidic sugars with a 9-carbon backbone, prominently expressed in animals of deuterostome lineage. Siglecs are the largest family of vertebrate endogenous receptors that recognize glycoconjugates containing sialic acids. Although a few Siglecs are well-conserved throughout vertebrate evolution and show similar binding preference regardless of the species of origin, most others, particularly the CD33-related subfamily of Siglecs, show marked inter-species differences in repertoire, sequence, and binding preference. The diversification of CD33-related Siglecs may be driven by direct competition against pathogens, and/or by necessity to catch up with the changing landscape of endogenous glycans, which may in turn be changing to escape exploitation by other pathogens.

Animals↗