Ionic strength dependent conformational changes of t-RNA studied by circular polarization of phosphorescence

Biochemistry ◽  
1982 ◽  
Vol 21 (10) ◽  
pp. 2573-2578 ◽  
Author(s):  
Nitza Steinberg ◽  
Ellen J. Wachtel ◽  
Ari Gafni
Keyword(s):  
Ionic Strength ◽  
Circular Polarization ◽  
Conformational Changes

Surface contraction of dividing newt eggs induced by lowering the external ionic strength or pH, or by trypsinization

1986 ◽  
Vol 82 (1) ◽  
pp. 143-154
Author(s):  
T. Kubota
Keyword(s):  
Ionic Strength ◽  
Conformational Changes ◽  
Time Course ◽  
Similar Type ◽  
Vitelline Membrane ◽  
Common Mechanism ◽  
Surface Material ◽  
Sucrose Medium ◽  
Saline Medium ◽  
Partial Reversal

As the first cleavage progresses, newt (Cynopus pyrrhogaster) eggs deprived of their vitelline membrane grow to expose the new, unpigmented surface to a saline medium full-strength Steinberg solution). Further exposure of these eggs to sucrose medium resulted in rapid and extensive contraction of the unpigmented surface. In the sucrose medium the contraction continued until the next cleavage, and eventually the eggs divided into many blastomeres. But partial reversal of the contraction was observed when, after brief treatment with sucrose medium, the eggs were returned to saline medium. This and other experiments indicated that the contraction was due to lowering of the extracellular ionic strength. A similar type of contraction was induced by acidification of the saline medium or by trypsinization. The contractions induced by these treatments did not absolutely require the presence of external Ca2+, had a rapid time course, and were restricted to the unpigmented region, suggesting that they had a common mechanism. Acidification of the egg cytoplasm with CO2 did not result in significant contraction. These findings, together with those of others, suggest that contraction of the unpigmented surface induced by these treatments is due to conformational changes of surface material.

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.

Temperature- and ionic strength-induced conformational changes in the lipid head group region of liposomes as suggested by zeta potential data

1991 ◽  
Vol 41 (2) ◽  
pp. 175-183 ◽  
Author(s):  
Kimiko Makino ◽  
Takeshi Yamada ◽  
Mariko Kimura ◽  
Takashi Oka ◽  
Hiroyuki Ohshima ◽  
...  
Keyword(s):  
Ionic Strength ◽  
Zeta Potential ◽  
Conformational Changes ◽  
Head Group ◽  
Lipid Head Group

scholarly journals Studies on the secondary structure of nuclear ribonucleic acids

1972 ◽  
Vol 130 (1) ◽  
pp. 11-17 ◽  
Author(s):  
M. Brentani ◽  
M. Kubota ◽  
R. Brentani
Keyword(s):  
Ionic Strength ◽  
Ribosomal Rna ◽  
Conformational Changes ◽  
Sedimentation Coefficient ◽  
Spectrophotometric Titration ◽  
Initial Value ◽  
Ribonucleic Acids ◽  
Rate Of Reaction ◽  
Liver Nuclei ◽  
Complex Polymers

Rat liver nuclei were separated into two fractions, the nucleolus and the nucleoplasm, by a combined salt–enzymic extraction. RNA was purified from both sources and analysed on sucrose density gradients. In both fractions a prominent heterogeneous RNA class with mean sedimentation coefficient of 18S was found. This material was analysed by measuring the rate of reaction with formaldehyde, the ultraviolet absorbance–temperature profile, the spectrophotometric observation of conformational changes as a function of pH, the spectrophotometric titration of uracil and guanine residues and the effect of both temperature and ionic strength on the spectrophotometric titration of cytosine residues. Nucleoplasmic 18S RNA fraction exhibited, on heating and also by adjustment of the pH to 2.5, a hyperchromicity of about 16 %, close to that observed, in control experiments, for ribosomal RNA (22%). Titration of cytosine residues in solutions containing 1mm-NaCl and 0.1m-NaCl yielded pK values equal to 4.41 and 3.84 respectively. These results suggest that this RNA fraction is composed of structurally complex polymers. The hypochromicity of the nucleolar 18S RNA fraction determined by heating or adjusting the pH to 2.5, was not greater than 6% of the initial value. The rate of reaction with formaldehyde was 88% of that observed for the hydrolysed 18S fraction which suggested only 12% hydrogen bonding. pK values for uracil and guanine residues were 10.1 and 10.05 respectively. Titration of cytosine residues yielded a pK of 4.10, which was found to be independent of temperature and ionic strength variations.

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