Phase relationships and thermodynamic properties in the Mn-Ni-C system

In the present work, phase relationships in selected phase regions of the Mn-Ni-C system have been investigated at 1073 and 1223 K by use of an equilibration technique. Alloys of Mn-Ni-C were prepared from pure Mn, Ni, and C powders by the powder metallurgy method. The phase identification of the heat-treated samples was carried out by scanning electron microscope (SEM) and transmission electron microscope (TEM). The main phase compositions of the alloys have been analyzed by X-ray diffraction (XRD). The experimental results show that the site fraction of Ni in the metallic sublattice of the carbides M₂₃C₆, M₇C₃, and M₅C₂ is quite low and the value is around 0.02 to 0.03. The thermodynamic activities of manganese in 16 different Mn-Ni-C alloys have been studied by solid-state galvanic cell technique with single-crystal CaF₂ as the solid electrolyte in the temperature range 940 to 1165 K. The results are discussed in light of the available thermochemical information.     

Structural and thermodynamic characteristics of the binding of the lambda N protein to a RNA hairpin

The specific binding of the lambda N protein to a 15 nucleotide RNA oligomer that forms a hairpin structure has been investigated by biophysical methods. Using fluorescence spectroscopy and equilibrium ultra-centrifugation, it was found that the N protein binds specifically to this RNA hairpin as a monomer. Circular dichroism experiments show that both the N protein and the RNA hairpin undergo structural change upon association of the complex.     

Comparison of cannabinoid binding sites in guinea-pig forebrain and small intestine

We have investigated the nature of cannabinoid receptors in guinea-pig small intestine by establishing whether this tissue contains cannabinoid receptors with similar binding properties to those of brain CB1 receptors. The cannabinoids used were the CB1-selective antagonist SR141716A, the CB2-selective antagonist SR144528, the novel cannabinoid receptor ligand, 6'-azidohex-2'-yne-delta8-tetrahydrocannabinol (O-1184), and the agonists CP55940, which binds equally well to CB1 and CB2 receptors, and WIN55212-2, which shows marginal CB2 selectivity. [3H]-CP55940 (1 nM) underwent extensive specific binding both to forebrain membranes (76.3%) and to membranes obtained by sucrose density gradient fractionation of homogenates of myenteric plexus-longitudinal muscle of guinea-pig small intestine (65.2%). Its binding capacity (Bmax) was higher in forebrain (4281 fmol mg(-1)) than in intestinal membranes (2092 fmol mg(-1)). However, the corresponding KD values were not significantly different from each other (2.29 and 1.75 nM respectively). Nor did the Ki values for its displacement by CP55940, WIN55212-2, O-1184, SR141716A and SR144528 from forebrain membranes (0.87, 4.15, 2.85, 5.32 and 371.9 respectively) differ significantly from the corresponding Ki values determined in experiments with intestinal membranes (0.99, 5.03, 3.16, 4.95 and 361.5 nM respectively). The Bmax values of [3H]-CP55940 and [3H]-SR141716A in forebrain membranes did not differ significantly from each other (4281 and 5658 fmol mg(-1)) but were both greater than the Bmax of [3H]-WIN55212-2 (2032 fmol mg(-1)). O-1184 (10 or 100 nM) produced parallel dextral shifts in the log concentration-response curves of WIN55212-2 and CP55940 for inhibition of electrically-evoked contractions of the myenteric plexus-longitudinal muscle preparation, its KD values being 0.20 nM (against WIN55212-2) and 0.89 nM (against CP55940). We conclude that cannabinoid binding sites in guinea-pig small intestine closely resemble CB1 binding sites of guinea-pig brain and that 0-1184 behaves as a cannabinoid receptor antagonist in the guinea-pig myenteric plexus-longitudinal muscle preparation.     

Chiral PAF agonists: synthesis, theoretical analysis of their stereoelectronic properties and structure activity relationships

A series of chiral PAF agonists were synthesized. Modifications at the PAF structure were undertaken as far as the C2 substituents and the onium head groups are concerned. In parallel, molecular modelling studies including a MOPAC geometry optimization and the analysis of the electrostatic potential were performed on the newly synthesized and on already known PAF agonists, in order to gain a better insight into the stereoelectronic features required for interaction with the PAF receptor.     

A study on the effect of deoxynivalenol on serotonin receptor binding in pig brain membranes

Central serotoninergic (5-hydroxytryptamine, 5HT) pathways are believed to be involved in the mechanisms of anorexia and/or emesis evoked by the trichothecene mycotoxin deoxynivalenol (DON). Using an in vitro membrane receptor binding assay, the competitive potency of DON was investigated against several radioactive ligands that have a high affinity for selective 5HT receptor subgroups. Receptor site densities and displacement profiles in twelve selected regions of pig brain were investigated. Overall, DON possessed only minimal efficacy to competently block any of the 5HT-ligands tested. IC50 values (50% inhibitory concentration) of at least 5 mM DON were required to inhibit binding, and in certain regions concentrations of 100 mM were ineffective. In comparison, several standard 5HT-antagonists showed 10(3)-10(5) times greater capability than DON to displace binding of these ligands. Because these results indicated DON possesses only weak affinity for the 5HT-receptor subtypes investigated here, this suggested that in vivo, unless relatively high concentrations of the toxin are present, its pharmacological effects may be mediated by mechanisms other than a functional interaction with serotoninergic receptors at the central level.     

Chaperone activity and structure of monomeric polypeptide binding domains of GroEL

The chaperonin GroEL is a large complex composed of 14 identical 57-kDa subunits that requires ATP and GroES for some of its activities. We find that a monomeric polypeptide corresponding to residues 191 to 345 has the activity of the tetradecamer both in facilitating the refolding of rhodanese and cyclophilin A in the absence of ATP and in catalyzing the unfolding of native barnase. Its crystal structure, solved at 2.5 A resolution, shows a well-ordered domain with the same fold as in intact GroEL. We have thus isolated the active site of the complex allosteric molecular chaperone, which functions as a "minichaperone." This has mechanistic implications: the presence of a central cavity in the GroEL complex is not essential for those representative activities in vitro, and neither are the allosteric properties. The function of the allosteric behavior on the binding of GroES and ATP must be to regulate the affinity of the protein for its various substrates in vivo, where the cavity may also be required for special functions.     

Neuropeptide FF receptors of mouse olfactory bulb: binding properties and stimulation of adenylate cyclase activity

Neuropeptide FF (NPFF) receptors have been characterized in mouse olfactory bulb membranes by using [125I][1DMe]Y8Fa. The specific binding of this NPFF analogue was time and concentration dependent, reversible, saturable, and of high affinity (Kd = 0.022 nM, Bmax = 56.4 fmol/mg protein). In olfactory bulb membranes, NaCl increased the affinity of [125I][1DMe]Y8Fa by decreasing the dissociation rate constant (k-1). In contrast, the nonhydrolyzable analogue of GTP, Gpp[NH]p, decreased the maximal number of binding sites suggesting a coupling of NPFF receptors to a G-protein. In mouse olfactory bulb and spinal cord membranes, NPFF analogues stimulated adenylate cyclase activity in a time- and dose-dependent manner, whereas in the cerebellum, which does not possess NPFF receptors, low cAMP production was stimulated by NPFF. Our data are consistent with guanine nucleotide binding protein regulation of NPFF receptors positively coupled to adenylate cyclase.     

Controlling insulin-like growth factor activity and the modulation of insulin-like growth factor binding protein and receptor binding

The insulin-like growth factors (IGF) and insulin perform seemingly unique roles by causing the same metabolic effect: cellular hypertrophy. Although overlapping, there are different consequences to cellular hypertrophy induced by IGF and that induced by insulin. The IGF enhance the cell hypertrophy that is requisite for cell survival, hyperplasia, and differentiation, and insulin enhances cell hypertrophy primarily as a means to increase nutrient stores. The effects of IGF and insulin are controlled by the segregation of their receptors between different cell types. A model is discussed that describes the need for three hormones (IGF-I, IGF-II, and insulin) to control nutrient partitioning. Insulin receptor localization, as well as an episodic mode of secretion, evolved to perform the short-term action of clearing excess nutrients from the circulation. In contrast, a complex and interactive set of factors ensure that maximal IGF activity occurs only when conditions are optimal for growth. A relatively invariant rate of secretion and the IGF binding proteins serve to maintain a large mutable pool of IGF. This pool exists to ensure a constant supply of IGF to maintain the basal metabolic rate and to ensure that, once a cell begins to proliferate or differentiate, adequate exposure is available to complete the process even after severe short-term physiological insults. The IGF concentrations only change in response to prolonged differences in protein and energy availabilities, environmental and body temperatures, and external stress. Also, evidence is now emerging that describes a discrete role for trace nutrients in the regulation of IGF activity. In this latter regard, zinc has the notable role of targeting IGF binding proteins to the cell surface. New data are presented showing that zinc also changes the affinity of the type 1 IGF receptor and cell-associated IGF binding proteins to optimize IGF activity.     

Chromatographic indexes on immobilized artificial membranes for local anesthetics: relationships with activity data on closed sodium channels

PURPOSE: To elucidate the effectiveness of the different parameters for the prediction of biological activity, the n-octanol/buffer partition coefficients and theoretical calculated lipophilicity parameters of thirteen local anesthetic drugs (LAs), including two beta-blockers, were compared to the affinity values for phospholipids, calculated by a recent technique. METHODS: Interactions with phospholipids were measured by high performance liquid chromatography on a stationary phase made up of phospholipids, the so-called "Immobilized Artificial Membrane" (IAM). Reference lipophilicity parameters were measured by shake-flask method between n-octanol and buffer phases. RESULTS: Interactions with phospholipids were predicted from log P for all compounds except tocainide, which also showed additive polar extra-interactions. Moreover, when the retention on Immobilized Artificial Membrane (IAM) phase was mainly lipophilicity-based, a unique scale included the correlation between log kwIAM and log P values, for both LAs (bases) and the structurally unrelated (nonionizable and acidic) compounds previously studied. IAM interaction values for LAs were predictive of the partition measures on liposome membranes already reported in literature. The half-blocking doses for closed sodium channel, corrected for ionization at pH 7.4, were successfully correlated with the respective IAM values for eleven compounds while procaine and tetracaine, which are ester-linked compounds and have a p-amino group as well, gave more potent results than predicted by phospholipid interactions. CONCLUSIONS: The IAM chromatographic parameters were much more effective than reference lipophilicity values in describing partition on model membranes and in predicting pharmacological potency on closed sodium channels.     

High-resolution structure of a polyomavirus VP1-oligosaccharide complex: implications for assembly and receptor binding

The crystal structure of a recombinant polyomavirus VP1 pentamer (residues 32-320) in complex with a branched disialylated hexasaccharide receptor fragment has been determined at 1.9 A resolution. The result extends our understanding of oligosaccharide receptor recognition. It also suggests a mechanism for enhancing the fidelity of virus assembly. We have previously described the structure of the complete polyomavirus particle complexed with this receptor fragment at 3.65 A. The model presented here offers a much more refined view of the interactions that determine carbohydrate recognition and allows us to assign additional specific contacts, in particular those involving the (alpha2,6)-linked, branching sialic acid. The structure of the unliganded VP1 pentamer, determined independently, shows that the oligosaccharide fits into a preformed groove and induces no measurable structural rearrangements. A comparison with assembled VP1 in the virus capsid reveals a rearrangement of residues 32-45 at the base of the pentamer. This segment may help prevent the formation of incorrectly assembled particles by reducing the likelihood that the C-terminal arm will fold back into its pentamer of origin.     

Independent variation of beta-adrenergic receptor binding and catecholamine-stimulated adenylate cyclase activity in rat erythrocytes

The pharmacokinetics, following i.v. administration of (+)-propranolol (40 mg) have been compared to in vitro measurement of protein binding and biochemical parameters of liver function in six normal subjects and twenty patients with stable chronic liver disease. The clearance of (+)-propranolol decreased with evidence of increasing severity of impairment of liver function correlating significantly with a fall in serum albumin, a rise in bilirubin and a prolongation in prothrombin index. The clearance of (+)-propranolol correlated with and was numerically similar to the clearance of indocyanine green in normal subjects and also in patients with chronic liver disease. Protein binding was decreased in chronic liver disease, but this change was not related to changes in plasma proteins. In normal subjects and patients without ascites the volume of distribution increased with decreases in protein binding. Ascites was associated with a further increase in the volume of distribution. The considerable variation in half-life largely depends on changes in liver blood flow, the degree of protein binding and the plasma protein pool size.     

Preparation of mouse monoclonal antibodies to okadaic acid and their binding activity in organic solvents

Seven of 20 mouse monoclonal antibodies to OA, OA8-2, OA10-8, OA22-22, OA227-11, OA296-1, OA423-3, and OA958-2, were studied as to their binding to OA in organic solvents. OA423-3 (IgG1-kappa) and OA958-2 (IgG1-kappa) in 90-100% methanol retained their binding activities with both immobilized and free antibodies. Whereas OA8-2 (IgG2a-kappa), OA10-8 (IgG1-kappa), OA22-22 (IgG2a-kappa), OA227-11 (IgG1-kappa), and OA296-1 (IgM-kappa) did not bind to OA in over 50-60% methanol. The results of a non-competitive inhibition assay for OA indicated that in a methanolic or ethanolic solution, the binding ability of immobilized OA423-3 decreased as the concentration of each alcohol increased. The concentration of OA at the midpoint between the upper and lower plateaus of the inhibition curve was 0.18 ng/ml in 0% methanol and 570 ng/ml in 100%, respectively. In 0-50% of each of acetone, diethyl ether, and benzene in methanol, the binding ability of OA423-3 remained at the level in 100% methanol. OA958-2 showed similar binding properties to OA423-3. No relationship between the subclass of the immunoglobulin and the binding activity of the antibody in organic solvents was observed. These results indicate that the OA423-3 and OA958-2 antibodies are useful for the development of a new ELISA method for OA in organic solvents.     

Vascular endothelial growth factor: crystal structure and functional mapping of the kinase domain receptor binding site

Vascular endothelial growth factor (VEGF) is a homodimeric member of the cystine knot family of growth factors, with limited sequence homology to platelet-derived growth factor (PDGF) and transforming growth factor beta2 (TGF-beta). We have determined its crystal structure at a resolution of 2.5 A, and identified its kinase domain receptor (KDR) binding site using mutational analysis. Overall, the VEGF monomer resembles that of PDGF, but its N-terminal segment is helical rather than extended. The dimerization mode of VEGF is similar to that of PDGF and very different from that of TGF-beta. Mutational analysis of VEGF reveals that symmetrical binding sites for KDR are located at each pole of the VEGF homodimer. Each site contains two functional "hot spots" composed of binding determinants presented across the subunit interface. The two most important determinants are located within the largest hot spot on a short, three-stranded sheet that is conserved in PDGF and TGF-beta. Functional analysis of the binding epitopes for two receptor-blocking antibodies reveal different binding determinants near each of the KDR binding hot spots.     

In vitro platelet-activating factor receptor binding inhibitory activity of pinusolide derivatives: a structure-activity study

Pinusolide, a labdane-type diterpene lactone isolated from Biota orientalis, was found to be a potent platelet-activating factor (PAF) receptor binding antagonist. To investigate the structure-activity relationship and find derivatives with improved pharmacological profiles, 17 pinusolide derivatives were prepared and tested for their ability to inhibit the PAF receptor binding. The results demonstrated that the carboxymethyl ester group at C-19, the integrity of the alpha,beta-unsaturated butenolide ring, and the exocyclic olefinic function of pinusolide are all necessary for its maximum PAF receptor binding inhibitory activity. Among the derivatives, the 17-nor-8-oxo derivative 8 was found to be as potent as pinusolide. The results also suggested that several derivatives warrant further pharmaceutical and pharmacological studies due to their improved water solubility (8 and 11) and apparent lack of susceptibility to Michael-type nucleophilic addition (13 and 18).     

Synthesis of structural analogues of leukotriene B4 and their receptor binding activity

Structural analogues of leukotriene B4 (LTB4) were designed based on the plausible conformation of LTB4 (1). Joining C-7-C-9 of the conformer A or B into an aromatic ring system led to the discovery of benzene analogues 2, 4 and 6a. Joining C-4-C-9 of the conformer C or D into an aromatic ring system led to the discovery of analogues 3, 5 and 7. The compounds examined in this study were evaluated as to their inhibition of [3H] LTB4 binding to human neutrophils, and by a secondary intact human neutrophil functional assay for agonist/antagonist activity. The first analogues prepared, compounds 2-7, demonstrated moderate potency in the LTB4 receptor binding assay. The modification of these compounds by the introduction of another substituent into the aromatic ring produced a marked increase in receptor binding (28c, IC50 = 0.020 microM; 38c, IC50 = 0.020 microM; 52a, IC50 = 0.020 microM; 52b, IC50 = 0.018 microM). Most of these structural analogues of LTB4 demonstrated agonist activity. Of the analogues prepared in this study, only compound 57 demonstrated weak LTB4 receptor antagonist activity, at 10 microM.     

Distribution of cholecystokinin immunoreactivity in the BALB/c mouse forebrain: an immunocytochemical study

The present study describes cholecystokinin (CCK) immunoreactivity (CCK-IR) distribution in the brains of control and colchicine-treated mice. In the brains of control mice, the CCK-IR strongly revealed numerous axons and terminals. Perikarya exhibiting a faint to moderate immunoreactivity were also observed in areas such as cortices, hippocampus, amygdala, septum, and thalamus. The colchicine treatment did not seem to notably affect the brain CCK-IR innervation, but resulted in profound changes of the perikaryal staining. Indeed, the regions, which contained numerous moderately stained perikarya in the control animals, exhibited after colchicine treatment immunoreactive perikarya intensely stained but only in moderate number. This feature obviously appeared in the cortex in which, in addition to strongly stained perikarya, colchicine induced the appearance of numerous CCK-IR hillocks. In the lateral amygdala and thalamus of colchicine-treated animals, the somatic immunoreactivity was considerably decreased. The regions, such as paraventricular hypothalamic nucleus and bed nucleus of the stria terminalis, which in the control animals did not exhibit any stained perikaryon, showed a high number of strongly stained cell bodies after colchicine treatment. This study, mapping the mouse forebrain CCK-IR, demonstrated a wide distribution of this peptide. Moreover, CCK-IR is spontaneously visible in neurons of untreated mouse in some brain areas previously shown in the rat to exhibit CCK mRNA, but no clear perikaryal CCK-IR even after colchicine treatment.