(1/8610) Activity in saline of phthalylated or succinylated derivatives of mycobacterial water-soluble adjuvant.
A water-soluble fraction (WSA) of the cell wall can substitute for mycobacterial cells in Freund complete adjuvant. However, when WSA is administered in saline instead of in a water-in-oil emulsion, its adjuvant activity is very weak, and under certain experimental conditions it can even inhibit the humoral immune response. The data reported in the present study show that after treatment by phthalic or succinic anhydride the adjuvant activity of WSA was markedly changed, since high levels of circulating antibodies were produced when these derivatives were administered with an antigen in an aqueous medium. Moreover, the antigenic determinants of WSA were modified and acylated WSA had no tuberculin-like activity. (+info)
(2/8610) Calorimetric studies on the stability of the ribosome-inactivating protein abrin II: effects of pH and ligand binding.
The effects of pH and ligand binding on the stability of abrin II, a heterodimeric ribosome-inactivating protein, and its subunits have been studied using high-sensitivity differential scanning calorimetry. At pH7.2, the calorimetric scan consists of two transitions, which correspond to the B-subunit [transition temperature (Tm) 319.2K] and the A-subunit (Tm 324.6K) of abrin II, as also confirmed by studies on the isolated A-subunit. The calorimetric enthalpy of the isolated A-subunit of abrin II is similar to that of the higher-temperature transition. However, its Tm is 2.4K lower than that of the higher-temperature peak of intact abrin II. This indicates that there is some interaction between the two subunits. Abrin II displays increased stability as the pH is decreased to 4.5. Lactose increases the Tm values as well as the enthalpies of both transitions. This effect is more pronounced at pH7.2 than at pH4.5. This suggests that ligand binding stabilizes the native conformation of abrin II. Analysis of the B-subunit transition temperature as a function of lactose concentration suggests that two lactose molecules bind to one molecule of abrin II at pH7.2. The presence of two binding sites for lactose on the abrin II molecule is also indicated by isothermal titration calorimetry. Plotting DeltaHm (the molar transition enthalpy at Tm) against Tm yielded values for DeltaCp (change in excess heat capacity) of 27+/-2 kJ.mol-1.K-1 for the B-subunit and 20+/-1 kJ.mol-1.K-1 for the A-subunit. These values have been used to calculate the thermal stability of abrin II and to surmise the mechanism of its transmembrane translocation. (+info)
(3/8610) Treating the syndrome of inappropriate ADH secretion with isotonic saline.
It has been widely accepted that there is little use for saline treatment in the syndrome of inappropriate secretion of ADH (SIADH). However, having observed that most SIADH patients increased their plasma sodium (PNa) after 2 l isotonic saline over 24 h, we investigated whether urine osmolality or the sum of urinary sodium and potassium (UNa + K) predicted this response, in 17 consecutive patients with chronic SIADH. The initial measure of urinary sodium plus potassium (UNa + K t0) was weakly correlated to the change in PNa (DPNa) after infusion (r = -0.51; p < 0.05), while initial urine osmolality (UOSM t0) was a much better predictor (y = -0.024x + 12.90; r = -0.81; p < 0.001). The lack of predictive value for UNa + K t0 was probably because urine electrolyte concentrations were not maximal for the corresponding initial UOSM. This reflects differences in salt intake between the patients. The theoretical maximal value for UNa + K t0 (th max UNa + K t0) for a given USOM t0, was as good a predictor as UOSM t0 (th max UNa + K vs. DPNa: r = -0.81; p < 0.001). A theoretical model describing the effect of 2 l isotonic saline infusion on DPNa as a function of UNa + K, produced values comparable to those observed in our patients. Only 6/17 patients, those with UOSM > 530 mOsm/kg, had their hyponatraemia aggravated by 2 l isotonic saline. Many SIADH patients have lower UOSM; in most such patients, 2 l of isotonic saline will improve PNa. (+info)
(4/8610) H5 Histone and DNA-relaxing enzyme of chicken erythrocytes. Interaction with superhelical DNA.
The interaction of closed circular duplex DNA with the lysine-rich H5 histone fraction of avian erythrocytes has been studied. H5, like H1 histone, interacts preferentially with superhelical DNA. The extent of interaction increases with increasing negative or positive superhelicity. Salt-extracted lysine-rich histones show the same specificity for interaction with superhelices as do acid-extracted preparations. Chicken erythrocyte nuclei contain DNA-relaxing enzyme. This enzyme is extracted from the nuclei at lower salt concentrations than those required to extract H1 and H5 histones and is, therefore, probably a function of a protein distinct from H1 and H5 histones. (+info)
(5/8610) Aggregation of deoxyhemoglobin S at low concentrations.
The self-association of deoxyhemoglobin S was measured in dilute solutions (0 to 5 g/dl) by Rayleigh light scattering at 630 nm and osmometry in 0.05 M potassium phosphate buffer (pH 7.35). Weight and number average molecular weights (Mw and Mn, respectively) and the second or higher virial coefficients, B' were determined. No experimentally significant differences were observed between oxy- and deoxy-Hb S up to the concentration of 2 g/dl; their apparent average molecular weights were within experimental error. Above that concentration, both Mn and Mw of deoxy-Hb S were significantly different from that of oxy-Hb S. The negative second viral coefficent of deoxy-Hb S, observed by both techniques, is consistent with the self-association of this protein. The lack of effect of 0.4 M propylurea on the state of aggregation and the significant influence of 0.1 M NaCl suggests that polar interactions are involved in formation of these aggregates. (+info)
(6/8610) Characterization of nuclear structures containing superhelical DNA.
Structures resembling nuclei but depleted of protein may be released by gently lysing cells in solutions containing non-ionic detergents and high concentrations of salt. These nucleoids sediment in gradients containing intercalating agents in a manner characteristic of DNA that is intact, supercoiled and circular. The concentration of salt present during isolation of human nucleoids affects their protein content. When made in I-95 M NaCl they lack histones and most of the proteins characteristic of chromatin; in 1-0 M NaCl they contain variable amounts of histones. The effects of various treatments on nucleoid integrity were investigated. (+info)
(7/8610) Electrostatic interactions during activation of coagulation factor IX via the tissue factor pathway: effect of univalent salts.
Interaction between the Gla-domain of coagulation proteins and negatively charged phospholipid membranes is essential for blood coagulation reactions. The interaction is calcium-dependent and mediated both by electrostatic and hydrophobic forces. This report focuses on the electrostatic component of factor IX activation via the extrinsic pathway. Effective charges during the reaction are measured by ionic titration of activity, according to the Debye-Huckel and Gouy-Chapman models. Rates of activation decrease with ionic strength independently of the type of monovalent salt used to control ionic strength. Moreover, the effect of ionic strength decreases at concentrations of charged phospholipid approaching saturation levels, indicating that membrane charges participate directly in the ionic interaction measured. The effective charge on calcium-bound factor IX during activation on phospholipid membranes is 0.95+/-0.1. Possible sites mediating contacts between the Gla-domain and membranes are selected by geometrical criteria in several metal-bound Gla-domain structures. A pocket with a solvent opening-pore of area 24-38 A2 is found in the Gla-domain of factors IX, VII, and prothrombin. The pocket contains atoms with negative partial charges, including carboxylate oxygens from Gla residues, and has a volume of 57-114 A3, sufficient to accommodate additional calcium atoms. These studies demonstrate that electrostatic forces modify the activity coefficient of factor IX during functional interactions and suggest a conserved pocket motif as the contact site between the calcium-bound Gla-domain and charged membranes. (+info)
(8/8610) Electrical and mechanical responses to diltiazem in potassium depolarized myocardium of the guinea pig.
Effects of diltiazem on the electrical and mechanical activities of guinea pig papillary muscle were investigated in K-rich Tyrode's solution (Kc1 12.7 mM). The electrical properties of cell membrane in K-rich solution were also examined in the ventricular muscle fibers. It was found that the overshoot as well as the maximum rate of rise (Vmax) of the action potential were highly sensitive to the extracellular concentration of CaC12 in K-rich solution. Vmax was also affected by NaC1. Diltiazem at a lower concentration (1.1 X 10(-7) M) caused a reduction in the contractile force of K-depolarized papillary muscle without producing significant changes in the resting and action potentials. In the presence of a higher concentration of diltiazem (1.1 X 10(-5) M), the contractile force decreased concurrently with the change in the action potential. Addition of CaC12 restored the original strength of contraction in parallel to the recovery of the action potential, especially in its overshoot and Vmax. From these results, it is inferred that diltiazem may decrease the contractile force of guinea pig papillary muscle either by interfering with the intrasmembrane calcium influx or by intracellularly reducing the free calcium ion concentration in the myoplasm. (+info)