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B Halle

Publications and source records attributed to B Halle.

32 records · Page 2Linked to original sources
PubMed1995

Protein hydration dynamics in aqueous solution: a comparison of bovine pancreatic trypsin inhibitor and ubiquitin by oxygen-17 spin relaxation dispersion.

Water oxygen-17 spin relaxation was used to study hydration and dynamics of the globular proteins bovine pancreatic trypsin inhibitor (BPTI) and ubiquitin in aqueous solution. The frequency dispersion of the longitudinal and transverse relaxation rates was measured over the Larmor frequency range 2.6 to 49 MHz in the pD range 2 to 11 at 27 degrees C. While the protein-induced relaxation enhancement was similar for the two proteins at high frequencies, it was an order of magnitude smaller for ubiquitin than for BPTI at low frequencies. This difference was ascribed to the absence, in ubiquitin, of highly ordered internal water molecules, which are known to be present in BPTI and in most other globular proteins. These observations demonstrate that the water relaxation dispersion in protein solutions is essentially due to a few structural water molecules buried within the protein matrix, but exchanging rapidly with the external water. The relaxation data indicate that the internal water molecules of BPTI exchange with bulk water on the time-scale 10(-8) to 10(-6) second thus lowering the recently reported upper bound on the residence time of these internal water molecules by four orders of magnitude, and implying that local unfolding occurs on the submicrosecond time-scale. The water molecules residing at the surface of the two proteins were found to be highly mobile, with an average rotational correlation time of approximately 20 picoseconds. For both proteins, the oxygen-17 relaxation depended only very weakly on pD, showing that ionic residues do not perturb hydration water dynamics more than other surface residues. We believe that the present results resolve the long-standing controversy regarding the mechanism behind the spin relaxation dispersion of water nuclei in protein solutions, thus establishing oxygen-17 relaxation as a powerful tool for studies of structurally and functionally important water molecules in proteins and other biomolecules.

Aprotinin↗
PubMed1995

Hydrogen exchange and protein hydration: the deuteron spin relaxation dispersions of bovine pancreatic trypsin inhibitor and ubiquitin.

Water deuteron (2H) spin relaxation was used to study hydrogen exchange, hydration, and protein dynamics in aqueous solutions of the globular proteins bovine pancreatic trypsin inhibitor (BPTI) and ubiquitin. The frequency dispersion of the longitudinal 2H relaxation rate was measured in the pD range 2 to 11 at 27 degrees C. In contrast to the previously reported water 17O relaxation dispersion from the same samples, the 2H dispersion depends strongly on pD. This pD dependence is due to labile protein deuterons in acidic side-chains and surface peptide groups, which exchange rapidly with water deuterons. The pD dependence of the 2H relaxation in BPTI solutions could be quantitatively accounted for in terms of known pK values and hydrogen exchange rate constants. For ubiquitin, labile protein deuterons contribute importantly to the 2H relaxation dispersion even in the neutral pD range. The 2H relaxation data also provided information about the orientational order and internal motion of OD and ND bonds in side-chains and surface peptides. A comparison of the water contribution to the 2H dispersion with the 17O dispersion indicates that one of the four internal water molecules of BPTI, presumably the deeply buried water molecule W122, exchanges more slowly (10(-6) to 10(-4) second) than the other three (10(-8) to 10(-6) second).

Aprotinin↗
PubMed1995

A new view of water dynamics in immobilized proteins.

The inflection frequency of the deuteron magnetic relaxation dispersion from water in rotationally immobilized protein samples has recently been found to be essentially independent of temperature and protein structure. This remarkable invariance has been interpreted in terms of a universal residence time of 1 microseconds for protein-associated water molecules. We demonstrate here that this interpretation is an artifact of the conventional perturbation theory of spin relaxation, which is not valid for rotationally immobile proteins. Using a newly developed non-perturbative, stochastic theory of spin relaxation, we identify the apparent correlation time of 1 microseconds with the inverse of the nuclear quadrupole frequency, thus explaining its invariance. The observed dispersion profiles are consistent with a broad distribution of residence times, spanning the microseconds range. Furthermore, we argue that the deuteron dispersion is due to buried water molecules rather than to the traditional surface hydration previously invoked, and that the contribution from rapidly exchanging protein hydrogens cannot be neglected. The conclusions of the present work are also relevant to proton relaxation in immobilized protein samples and to magnetic resonance imaging of soft tissue.

Artifacts↗
PubMed1984

The Smoluchowski-Poisson-Boltzmann description of ion diffusion at charged interfaces.

A theoretical description of ion diffusion in the electric field set up by the double layer in the neighborhood of a charged interface is presented. Such a description is needed for the understanding of diffusion-controlled chemical kinetics and transport of ionic species in a variety of systems of interest in biophysics, electrochemistry, and colloid science. The ion dynamics are taken to be governed by the Smoluchowski diffusion equation and the average electrostatic field is obtained from the nonlinear Poisson-Boltzmann equation. Diffusion in finite regions with partially absorbing boundaries of planar, cylindrical, or spherical geometry is considered. The complete analytical solution of the Smoluchowski-Poisson-Boltzmann equation for counterions between two planar charged interfaces is given. Simple expressions are derived for certain useful integral quantities, viz., mean absorption times and absorption probabilities, in all geometries considered. Finally, lateral counterion diffusion and its consequences for surface re-encounter-enhanced chemoreception is considered.

Diffusion↗
PubMed1978

Chloride ion binding to human plasma albumin from chlorine-35 quadrupole relaxation.

The 35Cl nuclear magnetic quadrupole relaxation enhancement on binding of chloride ions to human plasma albumin (HPA) has been studied under conditions of variable temperature, pH, ionic strength, protein, and sodium dodecyl sulfate concentration. A small number (less than 10) of chloride ions, most of which are bound to the primary detergent binding sites, contribute a major portion of the relaxation enhancement (greater than 80% at neutral pH). A comparison of the pH dependence of the relaxation rate with the hydrogen ion titration curve, which was determined and analyzed, identified ten lysyl and arginyl residues as being involved in the chloride ion binding. These data, in conjuction with NaDodSO4 titrations at different pH values and the amino acid sequence of HPA, suggests that the high-affinity chloride-binding sites are doubly cationic at neutral pH. An irreversible dimerization at acidic pH and 5 x 10(-5) m HPA was detected. The data also indicate the presence of internal modes of motion in the expanded forms of the HPA molecule, probably an independent reorientation of domains. The rate of exchange of chloride ions was shown to be much higher than the corresponding intrinsic relaxation rate in the temperature range 2--26 degrees C and pH values ranging from 4.0 to 10.5. No indications of protein-protein interaction could be found up to the physiological concentration of ca. 6 x 10(-4)m HPA at either neutral or alkaline pH. The mechanistic basis for HPA's exceptional capacity for binding of inorganic anions was discussed.

Chlorides↗
PubMed1970

Stereostethoscope.

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Auscultation↗