PubMed Health⌕ Search

Biomedical subjects

A Hvidt

Publications and source records attributed to A Hvidt.

13 recordsLinked to original sources
PubMed1980

Enzymes immobilized as crystals. Hydrogen isotope exchange of crystalline lysozyme.

Immobilization of enzymes by crystallization and subsequent cross-linking provide structures characterized by a regular three-dimensional molecular arrangement and a high packing density. Compared to randomly immobilized enzymes, such structures permit more detailed analysis of the variations in kinetic properties arising from the three-dimensional network or perturbations of the molecular conformations. To obtain information on the effect of crystallization on the dynamic properties of the folded peptide chain in an enzyme molecule, hydrogen exchange rates were measured for both dissolved and crystalline lysozyme over a wide range of pH. Using this method, which reflects molecular oscillations between closely related conformations, no differences were detected between lysozyme in crystalline and dissolved state.

Crystallization↗
PubMed1978

A contribution to the debate about hydrophobic effects.

Based on available measurements of the concentration dependence of the volume and the heat capacity of aqueous solutions of low molecular weight compounds it is suggested that non-polar molecules or non-polar groups in aqueous solution fluctuate between solvated and non-solvated states. The experimental data indicate that the change in standard free energy of the hydrophobic solvation is positive and so large that the solvation is incomplete even in the most dilute solutions studied. It is tentatively suggested that the hydrophobic solvation enhances the solubility in water of non-polar substances, and that the reason why non-polar groups in protein solutions are buried in the interior of the protein conformations is a low degree of solvation of these groups in the solvent exposed state.

Mathematics↗
PubMed1977

Physicochemical studies of a branched polypeptide antigen: poly(L-Tyr,L-Glu)-poly(DL-Ala)--poly(L-Lys).

The synthesis of a branched polypeptide, poly(L-Tyr,L-Glu)-poly(DL-Ala)--poly(L-Lys), is described. Physicochemical investigations of the polymer by means of hydrogen-deuterium exchange, potentiometric titrations, and viscosity measurements indicate a non-ordered, flexible conformation in aqueous solution, depending on pH and salt concentration. A hysteresis phenomenon observed in the titrations is tentatively ascribed to interactions between the sidechains, and in accordance with observations from the infrared spectrum of the polymer it is suggested that rather slow conformational changes of the polymer molecules occur in aqueous solutions. The immunochemical implications of the physiochemical findings are discussed with special reference to the concept of sequential and conformational determinants.

Alanine↗
PubMed1975

Hydrogen-exchange study of the conformational stability of human carbonic-anhydrase B and its metallocomplexes.

In the range of pH 4.6--8.8, 25 degrees C, the apoenzyme of carbonic anhydrase B shows no evidence of any gross conformational changes, as studied by the hydrogen-deuterium exchange method. At pH 4.6 the addition of Co(II), Cd(II) or Mn(II) to the apoenzyme results in a destabilization of the native protein conformation, but in the range of pH 5.5--8.8 these metal ions, and Zn(II), slightly increase the conformational stability of the protein, in so far as they reduce the probability phi of solvent exposure of the peptide groups. In comparison with other proteins studied, native carbonic anhydrase is characterized by a rather compact conformation; for half of the peptide groups the probability of solvent exposure is less than 10(-4), corresponding to changes in standard free energy larger than 5.5 kcal mol-1 (23 kJ mol-1) following the conformational transitions by which these groups are exposed to the solvent.

Apoenzymes↗