scholarly journals Effects of pH and ionic strength on the binding of l-tri-iodothyronine to the solubilized nuclear receptor

1985 ◽  
Vol 232 (3) ◽  
pp. 663-667 ◽  
Author(s):  
B D Wilson ◽  
W L Gent
Keyword(s):  
Ionic Strength ◽  
Nuclear Receptor ◽  
Conformational Changes ◽  
Association Constant ◽  
Receptor Site ◽  
Receptor Protein ◽  
Acidic Group ◽  
Receptor Concentration ◽  
Effects Of Ph ◽  
Apparent Association

K'A (apparent association constant) and Bmax. (total receptor concentration) describing the interaction of tri-iodothyronine (T3) and its solubilized rat liver nuclear receptor (R) are found to be moderately consistent in successive preparations, but both quantities diminished after a few days. To achieve comparability in the effects of ionic strength (I) and of pH on K'A and Bmax, appropriate measurements have been made simultaneously on single preparations. K'A and Bmax. were found to be effectively unchanged over the range I0.05-0.60. Both parameters have been measured over the range pH 6.4-9.0 and the values of K'A analysed in terms of the 4′-OH ionization of T3 and that of a cationic acidic group, shown to require pK' = 7.6. This group could be identified either with the terminal alpha-NH3+ of T3 or with a group (RH+) in the receptor site. On the balance of evidence the first possibility is the more likely, in which case the variation of Bmax. with pH is ascribed to conformational changes in the receptor protein.

scholarly journals Modification of glyceraldehyde 3-phosphate dehydrogenase activity by adsorption on phospholipid vesicles

1976 ◽  
Vol 159 (3) ◽  
pp. 627-631 ◽  
Author(s):  
M S Wooster ◽  
J M Wrigglesworth
Keyword(s):  
Ionic Strength ◽  
Dehydrogenase Activity ◽  
Association Constant ◽  
Phospholipid Vesicles ◽  
Kinetic Properties ◽  
Km Value ◽  
Triton X ◽  
Positively Charged ◽  
Apparent Association ◽  
Apparent Association Constant

1. The adsorption of [14C]carboxymethylated glyceraldehyde 3-phosphate dehydrogenase to negatively charged liposomes of phsphatidic acid/phosphatidylcholine (3:7, w/w) was investigated. The apparent association constant at I/2 = 60, pH 7.6, was 0.4 × 10(6)M-1. Adsorption decreased as ionic strength and pH were increased. 2. In the presence of negatively charged liposomes, the Km value for glyceraldehyde 3-phosphate of glyceraldehyde 3-phosphate dehydrogenase was increased and Vmax. decreased. In the presence of positively charged liposomes, the Km value for glyceraldehyde 3-phosphate decreased and there was no significant change in Vmax. Addition of Triton X-100 abolished the effect of both positively and negatively charged liposomes on the kinetic properties of the enzyme.

Correction of proton and Ca association constants of EGTA for temperature and ionic strength

1989 ◽  
Vol 256 (6) ◽  
pp. C1250-C1256 ◽  
Author(s):  
S. M. Harrison ◽  
D. M. Bers
Keyword(s):  
New York ◽  
Ionic Strength ◽  
Association Constant ◽  
Association Constants ◽  
Tetraacetic Acid ◽  
Critical Stability ◽  
Skinned Muscle ◽  
Skinned Muscle Fibers ◽  
Complex Solutions ◽  
Apparent Association

The association constants of ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) for protons and Ca can be used to calculate the apparent association constant of EGTA for Ca (K'CaEGTA). This value is often used in calculating the free [Ca2+] of complex solutions such as those used to determine the Ca sensitivity of skinned muscle fibers. As association constants are usually measured at 0.1 M ionic strength and between 20 and 25 degrees C, these constants must first be adjusted for conditions different from those at which they were measured, before calculation of K'CaEGTA. The proton and Ca association constants (and their delta H values) from A. E. Martell and R. M. Smith (Critical Stability Constants, New York: Plenum, vol. 1, 1974) adjusted for ionic strength and temperature using a semiempirical Debye-Huckel formalism and Van't Hoff isochore, respectively, closely describe the influence of both ionic strength and temperature on K'CaEGTA. Errors in the adjustment or calculation of association constants can dramatically affect the calculated value of K'CaEGTA and hence the calculated free [Ca2+] of complex solutions, such as those used to mimic the intracellular environment.

Effects of pH and ionic strength on the cation exchange capacity of soils with variable charge

Soil Research ◽  
1981 ◽  
Vol 19 (1) ◽  
pp. 93 ◽  
Author(s):  
GP Gillman
Keyword(s):  
Ionic Strength ◽  
Cation Exchange ◽  
Cation Exchange Capacity ◽  
Exchange Capacity ◽  
Surface Soils ◽  
Ph Values ◽  
Variable Charge ◽  
Effects Of Ph ◽  
Variable Charge Soils

The cation exchange capacity of six surface soils from north Queensland and Hawaii has been measured over a range of pH values (4-6) and ionic strength values (0.003-0.05). The results show that for variable charge soils, modest changes in electrolyte ionic strength are as important in their effect on caton exchange capacity as are changes in pH values.

scholarly journals Alkylation of glyceraldehyde-3-phosphate dehydrogenase with haloacetylphosphonates. An unusual pH-dependence

1991 ◽  
Vol 275 (3) ◽  
pp. 767-773 ◽  
Author(s):  
Y K Li ◽  
J Boggaram ◽  
L D Byers
Keyword(s):  
Isotope Effect ◽  
Rate Constant ◽  
Ph Dependence ◽  
Thiol Group ◽  
Order Rate Constant ◽  
Acidic Group ◽  
Irreversible Inhibitors ◽  
Effects Of Ph ◽  
Solvent Isotope ◽  
Bell Shaped Curve

Two new alkylating reagents, chloro- and bromo-acetylphosphonate, were found to be very effective thiol-blocking reagents. The pH-dependence of the reaction of BAP with 2,4-dinitrothiophenol (25 degrees C, I 0.5) shows a tailing bell-shaped curve (with a plateau at high pH) characteristic of two ionizing groups: the thiol group (pKa 3.2) and the phosphonate group (pKa2 4.6). The rate constant for the reaction of the monoanionic inhibitor with dinitrothiophenolate (k2 = 7 M-1.s-1) is 120 times larger than that of the dianionic species. The haloacetylphosphonates were found to be irreversible inhibitors of glyceraldehyde-3-phosphate dehydrogenase from a variety of sources. They react with the active-site thiol group (Cys-149) and are half-site reagents with yeast glyceraldehyde-3-phosphate dehydrogenase. Thus, when two of the identical four subunits are modified the enzyme is catalytically inactive. The effects of pH (7-10), 2H2O and NAD+ on the reaction with the yeast enzyme were examined in detail. NAD+ enhances the alkylation rates. The second-order rate constant does not show a simple sigmoidal dependence on pH but rather a tailing bell-shaped curve (pKa 7.0 and 8.4) qualitatively similar to that obtained with dinitrothiophenol. There is no significant solvent isotope effect on the limiting rate constants and a normal isotope effect on the two pKa values. The results are consistent with the more reactive enzyme species containing a thiolate and an acidic group that may either donate a proton to the dianionic haloacetylphosphonate or orient the inhibitor.

Evaluation of effects of pH and ionic strength on colloidal stability of IgG solutions by PEG-induced liquid-liquid phase separation

2016 ◽  
Vol 145 (18) ◽  
pp. 185101 ◽  
Author(s):  
Ronald W. Thompson ◽  
Ramil F. Latypov ◽  
Ying Wang ◽  
Aleksey Lomakin ◽  
Julie A. Meyer ◽  
...  
Keyword(s):  
Phase Separation ◽  
Ionic Strength ◽  
Liquid Phase ◽  
Colloidal Stability ◽  
Liquid Phase Separation ◽  
Effects Of Ph ◽  
Liquid Liquid Phase Separation

Effects of pH, aluminium, and soft water on larvae of the amphibians Bufo bufo and Triturus vulgaris

2006 ◽  
Vol 84 (11) ◽  
pp. 1668-1677 ◽  
Author(s):  
Jon K. Skei ◽  
Dag Dolmen
Keyword(s):  
Ionic Strength ◽  
High Mortality ◽  
Bufo Bufo ◽  
Soft Water ◽  
Internal Environment ◽  
Triturus Vulgaris ◽  
Effects Of Ph ◽  
Low Ionic Strength

Larval Bufo bufo (L., 1758) and Triturus vulgaris (L., 1758) were exposed to soft water (0.5 mg·L–1 Ca2+) experimentally acidified to pH 3.9 to 5.9 and total aluminium concentrations of <10, 150, and 300 µg·L–1. Below pH 4.5 both species experienced increased mortality. The LC50 (168 h) for <10 and 150 µg·L–1 Al was pH 4.3 and 4.1 for B. bufo and 4.2 and 4.1 for T. vulgaris. However, Al3+ increased the survival of both species, which may be due to the contribution of Al3+ to the ionic strength. No B. bufo larvae died at pH >4.5, whereas T. vulgaris at higher Al concentrations suffered relatively high mortality at pH 5.1–5.9, where Al occurs mainly as Al(OH)2+ and Al(OH)2+. Unlike external gills (T. vulgaris), internal gills (B. bufo) have their own internal environment and are probably better protected against the presence of these toxic Al species in the water. These Al species thus seem to be toxic to T. vulgaris larvae but not to B. bufo. Chloride was seen to be important for survival in water of low ionic strength, since the survival of T. vulgaris larvae, particularly at low Al concentration, increased at pH levels down to pH 4.3 when the water was acidified with HCl.

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