ChemInform Abstract: ON THE QUENCHER CONCENTRATION DEPENDENCE OF FLUORESCENCE QUENCHING: THE ROLE OF SOLUTION DIELECTRIC CONSTANT AND IONIC STRENGTH

Equilibrium study on complex formation of L-histidine with Pb(II), Cd(II), and Hg(II) has been investigated pH metrically in DMSO-water mixtures (0–60% v/v) at 303 K and 0.16 mol L−1 ionic strength. The predominant species detected for Pb(II) and Cd(II) are ML2H4, ML2H3, ML2H2, ML2H, and ML2 and those for Hg(II) are ML2H4, ML2H3, ML2, and ML. The appropriateness of experimental conditions is verified by introducing errors intentionally in the concentrations of ingredients. The models containing different numbers of species were refined by using the computer program MINIQUAD75. The best-fit chemical models were arrived at based on statistical parameters. The trend in variation of stability constants of the complexes with dielectric constant of the medium is attributed to the electrostatic and nonelectrostatic forces. The species distribution and the plausible equilibria for the formation of the species are also presented.

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cAMP induces a rapid and reversible modification of the chemotactic receptor in Dictyostelium discoideum.

The Journal of Cell Biology ◽

10.1083/jcb.100.3.715 ◽

1985 ◽

Vol 100 (3) ◽

pp. 715-720 ◽

Cited By ~ 39

Author(s):

C Klein ◽

J Lubs-Haukeness ◽

S Simons

Keyword(s):

Dictyostelium Discoideum ◽

Concentration Dependence ◽

Time Course ◽

Camp Synthesis ◽

Sds Page ◽

Reversible Modification ◽

Camp Receptor ◽

Camp Stimulation ◽

Stimulation Of

Stimulation, within 1 min after cAMP stimulation, of aggregation-competent Dictyostelium discoideum amebae was found to cause a rapid (within 1 min) modification of the cell's surface cAMP receptor. The modified receptor migrated on SDS PAGE as a 47,000-mol-wt protein, as opposed to a 45,000-mol-wt protein labeled on unstimulated cells. The length of time this modified receptor could be detected depended upon the strength of the cAMP stimulus: 3-4 min after treatment with 10(-7) M cAMP, cells no longer possessed the 47,000-mol-wt form of the cAMP receptor. Instead, the 45,000-mol-wt form was present. Stimulation of cells with 10(-5) M cAMP, however, resulted in the persistent (over 15 min) expression of the modified receptor. The time course, concentration dependence, and specificity of stimulus for this cAMP-induced shift in the cAMP receptor were found to parallel the cAMP-stimulated phosphorylation of a 47,000-mol-wt protein. In addition, both phenomena were shown to occur in the absence of endogenous cAMP synthesis. The possibility that the cAMP receptor is phosphorylated in response to cAMP stimulation, and the role of this event in cell desensitization, are discussed.

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Role of ionic strength in the kinetics of formation of the monochelate of nickel(II) with heptane-3,5-dione

International Journal of Chemical Kinetics ◽

10.1002/kin.550240405 ◽

1992 ◽

Vol 24 (4) ◽

pp. 359-368 ◽

Cited By ~ 5

Author(s):

María Luisa Moyá ◽

Amalia Rodriguez ◽

Francisco Sánchez ◽

Carlos Blanco ◽

Michael J. Hynes

Keyword(s):

Ionic Strength ◽

Kinetics Of Formation ◽

Kinetics Of

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Ethanol stability of casein micelles – a hypothesis concerning the role of calcium phosphate

Journal of Dairy Research ◽

10.1017/s0022029900025565 ◽

1987 ◽

Vol 54 (3) ◽

pp. 389-395 ◽

Cited By ~ 15

Author(s):

David S. Horne

Keyword(s):

Ionic Strength ◽

Skim Milk ◽

Buffer System ◽

Casein Micelles ◽

Buffer Solutions ◽

Relative Response ◽

Using Data ◽

The Stability ◽

Ethanol Stability

SummaryThe ethanol (EtOH) stability of skim milk and the stability towards aggregation of casein micelles diluted into ethanolic buffer solutions were compared using data obtained from previously published experiments. Differences in absolute stability and in relative response were observed when Ca2+ level and pH were adjusted, the buffer system results lying below those from skim milk in both cases. Increasing the ionic strength of skim milk adjusted to pH 7·0 lowered its EtOH stability whereas increasing the ionic strength of the diluting buffer increased the stability of the casein micelles. The hypothesis is put forward that the differences are due to the simultaneous precipitation of Ca phosphate when EtOH is added to skim milk. This draws calcium from the caseinate sites of the micelle, counteracting the destabilizing effects of the EtOH towards the micelle. Such removal and the consequent restructuring are kinetically controlled and micellar precipitation in skim milk finally occurs when the micellar coagulation time falls within the time scale of the restructuring reactions.

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