Cooperativity Index Research Articles

Effect of Limited Proteolysis on Phospholipase C-γ1 Kinetics

Phospholipase C-γ1 is a tightly regulated, multidomain protein that generates the second messengers inositol 1,4,5-trisphosphate and diacylglycerol. Kinetic analysis reveals that phospholipase C-γ1 displays apparent allosteric behavior. A previous study determined that proteolytic cleavage of the SH domain region of phospholipase C-γ1 yields an activated form of the enzyme (A. W. Fernald, G. A. Jones, and G. Carpenter Biochem. J. 302, 508, 1994). In this study, we show that activation of phospholipase C-γ1 by proteolysis decreases both the cooperativity and the half-maximal value of the enzyme for substrate. Kinetic analysis revealed that the mole fraction of phosphatidylinositol 4,5-bisphosphate (PIP2) that resulted in half-maximal PIP2 hydrolysis (S0.5) was lower for proteolyzed than uncleaved phospholipase C-γ1 (0.08 mole fraction vs 0.18 mole fraction of PIP2). The cooperativity index was lower for proteolyzed than full-length phospholipase C-γ1 (n = 2.5 vs n = 4). Kinetic analysis also revealed that the estimated dissociation constant was lower for phospholipase C-γ1 that had been subjected to proteolysis (0.1 mM vs 1.0 mM PIP2 for cleaved vs uncleaved phospholipase C-γ1, respectively). It was previously hypothesized that activation of phospholipase C-γ1 requires a conformational change that results in increased accessibility of substrate to the active site and that the SH domain of the enzyme is involved in the activation event. These experiments support the hypothesis that a portion of the protein covers the active site, allosterically inhibiting the enzyme, and that the removal of this “lid” domain activates the enzyme.

Scientific Production in Puerto Rico in Science and Technology during the Period 1990 to 1998

This paper analyses the research activity conducted by Puerto Rican scientists in science and technology in the period 1990 to 1998. The Science Citation Index (SCI) database was used to analyse scientific production by geographic area, type of insittution, document typology, language coverage, visibility of publications, subjects addressed and collaboration between local and international authors and institutions. Scientific production was observed to nearly double over the period studied and found to be concentrated in the academic sector, primarily in the city of San Juan, specifically in the University of Puerto Rico's Rio Piedras, Medical Sciences and Mayaguez campuses. Puerto Rican scientific production in the period studied was greater than in any other Caribbean country and the sixth largest in all of Latin America. Papers are mainly published in highly visible journals and scientific articles are the vehicle most commonly used to reach the scientific community. Co-operation indices between authors and institutions are high and the principal areas in which research is published are Medicine, Chemistry, Life Sciences and Physics.

Empirical validation of a two-state kinetic model for the B-Z transition of double-stranded poly[d(G-m5C)

A formula based on a first-order kinetic equation is derived to evaluate the rate constant of the B-Z transition of a synthetic double-stranded poly[d(G-m5C)] in terms of the salt concentration, the absolute temperature, and the cooperativity index. The validity of the formula was tested using circular dichroism spectroscopy after variation of the type of salt (NaCl, MgCl2), the salt concentration, and the temperature of the polynucleotide solution. A consequence of the proposed function is that in conditions of high salt there is a predictable salt threshold which determines the particular molecular mechanism of the B-Z transition. The paper also describes the way in which this threshold level is temperature dependent. A detailed comparison of our data with the experimental data found by other authors is given. The function agrees quantitatively with the experiments and explains the contrasting results found in the literature about the influence in the B-Z transition of both the temperature and the polymer size.

Transnational linkages of Indian science: A structural analysis

Abstract This study analyzes the pattern of transnational linkages of Indian science in eleven scientific fields (Mathematics, Physics, Chemistry, Biology, Earth & Space Science, Agriculture, Clinical Medicine, Biomedical Research, Engineering & Technology, Computer Science, and Materials Science) during the five-year period: 1990–1994. The following indicators are constructed to examine inter-field and inter-country differences in India’s transnational linkages: Internationalization index, Cooperation index, Cooperation extensiveness index and Affinity index. A four-category typology is proposed to classify the fields according to their propensities for attracting bilateral and multilateral cooperation with foreign countries. The structure of multidimensional system of relationships between India’s thirty-five most significant partner countries and eleven scientific fields is analyzed through correspondence analysis. A series of correspondence analyses are carried out on subsets of the multidimensional ...

Modulating the oxygen affinity of human fetal haemoglobin with synthetic allosteric modulators.

Improving the delivery of oxygen to the tissues by decreasing the oxygen affinity of haemoglobin has been a major aim of several laboratories over recent years because this may reduce the consequences of anaemia and/or improve tissue oxygenation in cases of decreased blood perfusion. Within the same context, lowering the oxygen affinity may prove valuable in the application of native or recombinant haemoglobin solutions as a blood substitute. The shift of the oxygen equilibrium curve to the right is obtained by various modulators. Among them, the bezafibrate derivatives are considered as a most interesting group. These principles are of the utmost importance in thalassaemia and other haemoglobinopathies where the beneficial effects of the compensatory synthesis of fetal haemoglobin are diminished by the increased oxygen affinity of this pigment. In this paper we present the results of a study initiated to determine whether a potent oxygen affinity modifier, RSR-4, could satisfactorily decrease the oxygen affinity of fetal haemoglobin, thus improving tissue oxygenation. The experiments were carried out on whole blood and on purified haemoglobin solutions and showed that the effector markedly decreased the oxygen affinity of HbF (from 18.7 to 3.73 mmHg in whole blood). At the same time the cooperativity index (n50) and the oxygen saturation levels remained within normal limits under the conditions of the main experiment. These observations have important implications for the potential application of oxygen affinity modifiers in vivo.

Entropy-Driven Intermediate Steps of Oxygenation May Regulate the Allosteric Behavior of Hemoglobin

When the oxygen binding isotherms of human, bovine and fallow deer (Dama-Dama) hemoglobins are measured at different temperatures either by optical or calorimetric techniques, analyses according to the Adair’s formalism show that at least one of the intermediate steps of ligation has a positive enthalpy change, i.e., absorbs rather than emitting heat, indicating that it is entropy rather than enthalpy driven (Bucci, E., et al. 1991. Biochemistry. 30:3195–3199; Bucci, E., et al. 1993. Biochemistry. 32:3519–3526; Johnson, C., et al. 1992. Biochemistry. 31:10074–10082; Johnson, C., et al. 1995. Biophys. Chem. 59:107–117). This phenomenon is confirmed in systems in which the β82 lysines of human hemoglobin are covalently cross-linked by acylation with dicarboxylic acids of increasing length, namely the fumaryl (four-carbon-long), adipoyl (six-carbon-long), and sebacoyl (10-carbon-long) residues. Consistently in all of the systems here reported, the enthalpy excursions are masked by compensatory entropy changes, which keep the free energy of ligand binding constant for the first three steps of oxygenation. Furthermore, the cooperativity index and the overall oxygen affinity seem to be correlated to the positive enthalpy excursions of the intermediate steps of ligation. Fumaryl-Hb (hemoglobin cross-linked with a fumaryl residue, four carbons) with the lowest absorption of heat has the highest affinity and lowest cooperativity index. Adipoyl-Hb (hemoglobin cross-linked with an adipoyl residue, six carbons) has the highest absorption of heat and the highest cooperativity index. It appears that nonuniform heat release by the intermediates of oxygenation is part of the allosteric phenomena in hemoglobin systems. There is not enough information that would allow assigning these phenomena to the interplay of the various conformations described for hemoglobin besides the classic T (Fermi et al. 1984. J. Mol. Biol. 175:159–174) and R (Shanaan. 1983. J. Mol. Biol. 171:31–59), as listed at the end of the Discussion. The possibility cannot be excluded that entropy-driven steps characterize new conformational transitions still to be described.

Calcium modulation of ligand affinity in the cyclic GMP-gated ion channels of cone photoreceptors.

To investigate modulation of the activation of cGMP-gated ion channels in cone photoreceptors, we measured currents in membrane patches detached from the outer segments of single cones isolated from striped bass retina. The sensitivity of these channels to activation by cGMP depends on the history of exposure to divalent cations of the membrane's cytoplasmic surface. In patches maintained in 20 microM Ca++ and 100 microM Mg++ after excision, the current amplitude dependence on cGMP is well described by a Hill equation with average values of K1/2, the concentration necessary to activate half the maximal current, of 86 microM and a cooperativity index, n, of 2.57. Exposing the patch to a solution free of divalent cations irreversibly increases the cGMP sensitivity; the average value of K1/2 shifts to 58.8 microM and n shifts to 1.8. Changes in cGMP sensitivity do not affect other functional parameters of the ion channels, such as the interaction and permeation of mono- and divalent cations. Modulation of cGMP activation depends on the action of an endogenous factor that progressively dissociates from the channel as Ca++ concentration is lowered below 1 microM. The activity of the endogenous modulator is not well mimicked by exogenously added calmodulin, although this protein competes with the endogenous modulator for a common binding site. Thus, the modulation of cGMP affinity in cones depends on the activity of an unidentified molecule that may not be calmodulin.

Cooperation Indices and Weighted Shapley Values

The weighted Shapley values are extended to situations defined by a cooperative game and a cooperation index. Two main axiomatic characterizations for the modified values are provided. We also develop further axiomatizations of the classical values and discuss two examples.

The stimulation of capsaicin-sensitive neurones in a vanilloid receptor-mediated fashion by pungent terpenoids possessing an unsaturated 1,4-dialdehyde moiety.

1. The irritant fungal terpenoid isovelleral caused protective eye-wiping movements in the rat upon intraocular instillation and showed cross-tachyphylaxis with capsaicin, the pungent principle in hot pepper. 2. Isovelleral induced a dose-dependent calcium uptake by rat dorsal root ganglion neurones cultured in vitro with an EC50 of 95 nM, which was fully inhibited by the competitive vanilloid receptor antagonist capsazepine. 3. Isovelleral inhibited specific binding of [3H]-resiniferatoxin (RTX), an ultrapotent capsaicin analogue, to rat trigeminal ganglion or spinal cord preparations with an IC50 of 5.2 microM; in experiments in which the concentration of [3H]-RTX was varied, isovelleral changed both the apparent affinity (from 16 pM to 37 pM) and the co-operativity index (from 2.1 to 1.5), but not the Bmax. 4. The affinity of isovelleral for inducing calcium uptake or inhibiting RTX binding was in very good agreement with the threshold dose (2.2. nmol) at which it provoked pungency on the human tongue. 5. For a series of 14 terpenoids with an unsaturated 1,4-dialdehyde, a good correlation was found between pungency on the human tongue and affinity for vanilloid receptors on the rat spinal cord. 6. The results suggest that isovelleral-like compounds produce their irritant effect by interacting with vanilloid receptors on capsaicin-sensitive sensory neurones. Since these pungent diterpenes are structurally distinct from the known classes of vanilloids, these data provide new insights into structure-activity relations and may afford new opportunities for the development of drugs targeting capsaicin-sensitive pathways.

Bibliometric indicators of production and usage of Archivos de Bronchoneumologia

We studied the bibliometric indexes referring to production and scientific output published in ARCHIVOS de BRONCONEUMOLOGIA. All issues published between 1993 and 1994 were studied with the exception of monógraphic or supplementary numbers. For each article we recorded article type, number of authors, authors' place of work, specialty, time until acceptance, time until publication, type of references, language of references, journal and year of references. For each year we calculated the productivity index and the cooperation index, or index of signers per work. We also determined the citation period for references, the Price index, and the insularity index. Productivity index was 1.97 in 1993 and 2.05 in 1994. The cooperation index for the two years reached 4.5 +/- 1.9 (1-10). Authors were widely distributed by provinces and by specialties, although "nuclei" of production could be identified. The citation half-life period was 5.67 years for references in 1993 and 5.94 years in 1994, and the Price index surpassed 40%. The insularity index was very low at 7.76%. In conclusion, the bibliometric indicators for production, readership and obsolescence for the two years analyzed indicate that ARCHIVOS de BRONCONEUMOLOGIA occupies an intermediate position in the ranking of Spanish medical journals.

Male genital modification

By modifying the body in meaningful ways, human beings establish their identity and social status. Lip plugs, ear plugs, penis sheaths, cosmetics, ornaments, scarification, body piercings, and genital modifications encode and transmit messages about age, sex, social status, health, and attractiveness from one individual to another. Through sociocultural sexual selection, male genital modification plays an important role as a sociosexual signal in both male competition and female mate choice. The reliability of the signal correlates with the cost of acquiring the trait. Women use a variety of cues to assess male quality. Male genital modification is one way that some women assess their mates. Extreme male genital modifications not only honestly advertise status, sexual potency, and ability to provide sexual satisfaction, they may provide a reliable index of male-female cooperation through the male's commitment to endure pain and risk.

A novel agonist, phorbol 12-phenylacetate 13-acetate 20-homovanillate, abolishes positive cooperativity of binding by the vanilloid receptor

Capsaicin binds to a specific recognition site, referred to as the vanilloid receptor, which it shares with the natural, ultrapotent agonist resiniferatoxin and with the competitive antagonist capsazepine. Upon binding to its receptor, capsaicin opens a cation channel leading to Ca 2+ influx. The binding of capsaicin or resiniferatoxin by the vanilloid receptor follows a sigmoidal saturation curve, indicative of positive cooperativity. The biological significance of this positive cooperative behaviour is unknown, as is the mechanism responsible for it. We have developed a novel ligand, phorbol 12-phenylacetate 13-acetate 20-homovanillate (PPAHV), which binds to cultured rat sensory neurons (with a K i of 3.1 ± 0.4 μM), and induces Ca 2+ uptake by them (with an ED 50 of 1.8 ± 0.3 μM) with similar affinities and in a non-cooperative manner (Hill coefficients are 0.99 and 1.06 for binding and Ca 2+ uptake, respectively). The behaviour of PPAHV thus contrasts with resiniferatoxin or capsaicin not only in the lack of cooperativity but also in the relative potencies for resiniferatoxin binding versus Ca 2+ uptake (resiniferatoxin is less potent and capsaicin is more potent for induction of Ca 2+ uptake than for binding). In further experiments in which the concentration of [ 3H]resiniferatoxin was varied, 1 μM PPAHV likewise reduced the cooperativity index that characterizes resiniferatoxin binding to rat spinal cord membranes from 2.3 ± 0.1 to 1.1 ± 0.2; in parallel experiments, neither capsaicin nor capsazepine (both at a concentration of 2 μM) affected binding cooperativity. Moreover, PPAHV (1 μM) turned the bi-phasic dissociation curve of resiniferatoxin into a monophasic curve, eliminating the second, slow-dissociation phase. The present results suggest that positive cooperativity is a ligand-induced feature rather than an inherent property of vanilloid receptors. A comparison of the spectrum of biological activity of ligands which bind to vanilloid receptors with different degrees of cooperativity may provide an approach to explore the functional significance of this binding behaviour.

Binding of neuroleptic drugs (trifluoperazine and rimcazole) to vanilloid receptors in porcine dorsal horn

Neuroleptic drugs were reported to modulate [ 3H]resiniferatoxin binding to vanilloid receptors in the spinal cord, with marked differences between rat and man. In the present study, we have used a [ 3H]resiniferatoxin binding assay using porcine dorsal horn membranes to explore further species differences in the interaction of neuroleptic drugs at spinal vanilloid receptors. Specific binding of 13 pM [ 3H]resiniferatoxin to porcine dorsal horn membranes (corresponding to a 7% fractional receptor occupancy) was affected by trifluoperazine in a bi-phasic fashion, with an initial 90% enhancement of binding preceding inhibition: a fit to the modified Hill equation yielded a cooperativity index of 1.8 and a K i of 5 μM. Under similar conditions, rimcazole, by contrast, had a monophasic effect: it enhanced but, up to 100 μM, did not inhibit [ 3H]resiniferatoxin binding. These results are in accord with previous findings in human spinal cord but contrast with those in the rat. In experiments in which the concentration of [ 3H]resiniferatoxin was varied, 20 μM trifluoperazine reduced the B max by 33% (from 181 ± 9 fmol/mg protein to 121 ± 5 fmol/mg protein) without a measurable change in affinity or cooperativity. In parallel experiments, by contrast, neither capsaicin nor capsazepine (both at a concentration of 10 μM) affected the B max or cooperativity but, as expected, reduced the affinity from 61 ± 8 pM to 120 ± 11 pM or to 101 ± 7 pM, respectively. Whereas vanilloid receptor agonists (resiniferatoxin and capsaicin) affected [ 3H]resiniferatoxin binding at low (approximately 7%) fractional receptor occupancies by the radioligand in a bi-phasic fashion, the competitive vanilloid receptor antagonist capsazepine failed to induce the initial binding enhancement. Thus, capsazepine appears to bind to vanilloid receptors in a non-cooperative fashion, or at least with much reduced positive cooperativity in this system. The mechanism by which neuroleptic drugs modulate resiniferatoxin binding is yet to be clarified and is clearly complicated as well as species-dependent; nonetheless, the reduced B max at higher concentrations suggests that it may at least in part be non-competitive.

Erythrocyte Na+–H+ exchanger kinetics and Na+–Li+ countertransport activity in essential hypertensive patients

The authors measured Na(+)-H+ exchanger kinetics together with Na(+)-Li+ countertransport V(max) in the erythrocytes of 21 subjects with essential hypertension and 16 normotensive control subjects. Na(+)-H+ exchange V(max) appeared to be increased in patients with essential hypertension, while the Na(+)-H+ exchanger affinity for intracellular proton sites (K50%) proved to be unchanged and the index of cooperativity among intracellular proton binding sites as measured by Hill's coefficient (Hill's n) decreased as compared with normotensive control subjects. Na(+)-Li+ countertransport V(max) appeared to be higher in patients with essential hypertension than in control subjects. The authors were unable to find any correlations between Na(+)-H+ exchanger kinetic parameters and metabolic variables such as parameters of insulin resistance and plasma lipids. On the basis of the data obtained, erythrocyte Na(+)-H+ exchanger activity was found to be abnormal in two kinetic variables in essential hypertensive patients and showed no simple linear correlations with the main variables of glucose metabolism, plasma lipids, renin or aldosterone.

Games and cooperation indices

We provide a model for quantitatively restricted cooperation. It leads to a modification of both the game and the Shapley value whose properties are studied, giving rise to an axiomatic characterization. An individually rational extension of the Myerson value is included, as well as a description of several former restriction methods that are shown to be generalized by our model.

Resiniferatoxin binding to vanilloid receptors in guinea pig and human airways.

We have used the [3H]resiniferatoxin (RTX) binding assay to characterize for the first time a vanilloid (capsaicin) receptor in tracheobronchial tissues of the guinea pig. Membranes obtained from the trachea and the main bronchi bound RTX with an affinity of 1 nM; the cooperativity index was close to unity, indicating noncooperative binding. Specific [3H]RTX binding was fully inhibited by capsaicin (Ki = 500 nM) and capsazepine (Ki = 100 nM), but it was not inhibited at all by the inactive RTX structural analog resiniferonol 9, 13, 14-orthophenylacetate (10 microM), confirming the specificity of the binding. Neither was RTX binding inhibited by the functional vanilloid antagonist ruthenium red (100 microM). The density of specific RTX binding sites was similar in the trachea (Bmax = 150 fmol/mg protein) and the bronchi (Bmax = 170 fmol/mg protein). In keeping with the marked resistance of hamsters to capsaicin actions, no specific RTX binding could be detected in the airways of this species. By contrast, we have been able to demonstrate specific RTX binding sites in human bronchi: the estimated affinity for RTX, 2 nM, was similar to that (7 nM) determined in guinea pig bronchi. We conclude that (1) the [3H]RTX binding assay affords a novel biochemical marker for vanilloid-sensitive nerves in the airways, and (2) this binding assay may be a useful tool to explore species-related differences in the expression and pharmacologic profile of vanilloid receptors in the airways.

Cooperation indices and coalitional value

We introduce an allocation rule for situations defined by a TUgame, a cooperation index and a coalition structure, and characterize it axiomatically. This rule is an extension of Owen's coalitional value; in fact, a variety of previously studied game situations is shown to be embodied and unified by our model.

Differential scanning calorimetric studies on binding of N-acetyl- d-glucosamine to lysozyme

Differential scanning calorimetric (DSC) measurements were performed on the thermal denaturation of lysozyme and lysozyme complexed with N-acetyl- d-glucosamine (GlcNAc) at pH 5.00 (acetate buffer), 4.25 and 2.25 (Gly-HCl buffer). DSC data have been analyzed to obtain denaturation temperature T d, enthalpy of denaturation ΔH d, heat capacity of denaturation ΔC pd and cooperativity index η. From these thermodynamic parameters, the binding constant K L and enthalpy of binding ΔH L, for the weak binding of lysozyme with GlcNAc have been determined. The values of K L and ΔH L at pH 5.00 and 298 K are 42 ± 4 M −1 and −24 ± 4 kJ mol −1, respectively, and agree very well with the experimentally determined values from equilibrium and other studies. The binding constant has also been estimated by simulating the DSC curve with varying values of K L ( T d) until it matches the experimental curve.

MATHEMATICAL MODELLING OF CELLULAR RESPONSES TO EXTERNAL SIGNALS

An empirical mathematical model is proposed to describe the response (growth rate, metabolic activity etc.) of a cell population to various intensities of an external signal (hormone, antibody, pharmacon etc.). The model is based on the assumption that the signal causes the target system to pass consecutively through i=1, …, N distinct population states having response coefficients Ri. Describing the interaction of the system with the signal according to the rules of chemical kinetics by two phenomenological parameters (k - sensitivity, n - cooperativity index) one arrives at a series expansion for Ri which is linear in the Ri’s but nonlinear with respect to k and n (“R-decomposition”). The pattern of expansion coefficients Ri is characteristic of a given signal and can be used to reveal similarities in the responses of the cell population to various signals. A user-friendly microcomputer program has been developed to fit the model equation to experimental data by means of constraint nonlinear regression analysis and to determine all characteristic curve parameters (number and location of extremal values, inflection points etc.). The robustness and benefit of the model is demonstrated by applications to various types of “exotic” dose-reponse-curves obtained from a neutral-red assay of fibroblasts. Similarities between response curves are studied.

Erythrocyte Na+‐H+ exchanger and Na+‐Li+ countertransport activity in primary aldosteronism

Several authors have described increased Na-H exchanger activity in essential hypertension but no data are available in secondary forms of hypertension such as primary aldosteronism. We measured Na-H exchanger kinetics together with Na-Li countertransport Vmax in the erythrocytes of eight patients with primary aldosteronism and in 15 normotensive control subjects. Plasma aldosterone, plasma renin and plasma potassium were also evaluated. Na-H exchanger Vmax appear to be increased in patients with primary aldosteronism and Hill's n, an index of co-operativity amongst intracellular proton binding sites, was significantly lower in patients than in controls. No statistically significant differences were found between affinity for intracellular protons (K50%) and for Na-Li countertransport Vmax between the two groups studied. We were unable to find any correlations between Na-H exchanger Vmax and Na-Li countertransport Vmax in the two groups considered as a whole. From the present data Na-H exchanger overactivity would not appear to be a specific feature of essential hypertension but seems to be characteristic in patients with primary aldosteronism.