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Physiological Ionic Strength (physiological + ionic_strength)

Distribution by Scientific Domains
Chemistry75%

Selected Abstracts

Determination of dissociation constants of folic acid, methotrexate, and other photolabile pteridines by pressure-assisted capillary electrophoresis

ELECTROPHORESIS, Issue 17 2006
Zoltán Szakács
Abstract Pressure-assisted CE (PACE) was applied to determine the previously inaccessible complete set of pK values for folic acid and eight related multiprotic compounds. PACE allowed the determination of all acidity macroconstants at low (,0.1,mM) concentration without interferences of selfassociation or photodegradation throughout the pH range. The accuracy of the constants was verified by NMR-pH, UV-pH, and potentiometric titrations and the data could be converted into physiological ionic strength. It was shown that even three overlapping pK values can be determined by CE with good precision (<0.06) and accuracy if an appropriately low sample throughput is used. Experimental aspects of PACE for the quantitation of acid,base properties are analyzed. The site-specific basicity data obtained for folic acid and methotrexate (MTX) reveal that apparently slight constitutional differences between folic acid and MTX carry highly different proton-binding propensities at analogous moieties, especially at the pteridine N1,locus, providing straightforward explanation for the distinctive binding to dihydrofolate reductase at the molecular level. [source]

Ribosome motions modulate electrostatic properties

BIOPOLYMERS, Issue 6 2004
Joanna Trylska
Abstract The electrostatic properties of the 70S ribosome of Thermus thermophilus were studied qualitatively by solving the Poisson,Boltzmann (PB) equation in aqueous solution and with physiological ionic strength. The electrostatic potential was calculated for conformations of the ribosome derived by recent normal mode analysis (Tama, F., et al. Proc Natl Acad Sci USA 2003 100, 9319,9323) of the ratchet-like reorganization that occurs during translocation (Frank, J.; Agrawal, R. K. Nature 2000 406, 318,322). To solve the PB equation, effective parameters (charges and radii), applicable to a highly charged backbone model of the ribosome, were developed. Regions of positive potential were found at the binding site of the elongation factors G and Tu, as well as where the release factors bind. Large positive potential areas are especially pronounced around the L11 and L6 proteins. The region around the L1 protein is also positively charged, supporting the idea that L1 may interact with the E-site tRNA during its release from the ribosome after translocation. Functional rearrangement of the ribosome leads to electrostatic changes which may help the translocation of the tRNAs during the elongation stage. © 2004 Wiley Periodicals, Inc. Biopolymers, 2004 [source]

Distance dependence and salt sensitivity of pairwise, coulombic interactions in a protein

PROTEIN SCIENCE, Issue 5 2002
Kelly K. Lee
Abstract Histidine pKa values were measured in charge-reversal (K78E, K97E, K127E, and K97E/K127E) and charge-neutralization (E10A, E101A, and R35A) mutants of staphylococcal nuclease (SNase) by 1H-NMR spectroscopy. Energies of interaction between pairs of charges (,Gij) were obtained from the shifts in pKa values relative to wild-type values. The data describe the distance dependence and salt sensitivity of pairwise coulombic interactions. Calculations with a continuum electrostatics method captured the experimental ,Gij when static structures were used and when the protein interior was treated empirically with a dielectric constant of 20. The ,Gij when rij , 10 Å were exaggerated slightly in the calculations. Coulomb's law with a dielectric constant near 80 and a Debye-Hückel term to account for screening by the ionic strength reproduced the salt sensitivity and distance dependence of ,Gij as well as the structure-based method. In their interactions with each other, surface charges behave as if immersed in water; the Debye length describes realistically the distance where interactions become negligible at a given ionic strength. On average, charges separated by distances (rij) ,5 Å interacted with ,Gij , 0.6 kcal/mole in 0.01 M KCl, but ,Gij decayed to ,0.10 kcal/mole when rij = 20 Å. In 0.10 M KCl, ,Gij , 0.10 kcal/mole when rij = 10 Å. In 1.5 M KCl, only short-range interactions with rij , 5 Å persisted. Although at physiological ionic strengths the interactions between charges separated by more than 10 Å are extremely weak, in situations where charge imbalance exists many weak interactions can cumulatively produce substantial effects. [source]

Heparin Dependent Coiled-Coil Formation

CHEMBIOCHEM, Issue 10 2008
Mark Nitz Dr.
Coiled-coil complexes: Heparin binding to designed peptides mediates the formation of a defined coil,coil complex through a polyelectrolyte interaction. The interaction occurs at physiological ionic strengths and is coupled to a ratiometric change in fluorescence. The interaction is specific to heparin over other common biological polyanions such as DNA, chondroitin sulfate A, or polyglutamic acid. [source]