Biomedical subjects

Y V Griko

Publications and source records attributed to Y V Griko.

4 recordsLinked to original sources

PubMed1992

Domains in lambda Cro repressor. A calorimetric study.

Thermodynamic properties of a mutant lambda Cro repressor with Cys replacing Val55 were studied calorimetrically. Formation of the S-S cross-link between neighboring Cys55 residues in this dimeric molecule leads to stabilization of a structure formed by the C-terminal parts of the two polypeptide chains, which behave as a single cooperative domain upon protein denaturation by heating. This composite domain is very stable at neutral pH and disrupts at 110 degrees C. The S-S-cross-linked tryptic fragment (residues 22-66), which includes this C-terminal domain, has similar stability. The N-terminal parts of the polypeptide chains do not form any stable structure when isolated, but in S-S-cross-linked dimer, they form a single cooperative block which melts in an all-or-none way 9 degrees C higher than the un-cross-linked protein. The observed cooperation of the distant N-terminal parts in dimer raises questions regarding lambda Cro repressor structure in solution.

Calorimetry↗

PubMed1992

Calorimetric study of the heat and cold denaturation of beta-lactoglobulin.

Temperature-induced changes of the states of beta-lactoglobulin have been studied calorimetrically. In the presence of a high concentration of urea this protein shows not only heat but also cold denaturation. Its heat denaturation is approximated very closely by a two-state transition, while the cold denaturation deviates considerably from the two-state transition and this deviation increases as the temperature decreases. The heat effect of cold denaturation is opposite in sign to that of heat denaturation and is noticeably larger in magnitude. This difference in magnitude is caused by the temperature-dependent negative heat effect of additional binding of urea to the polypeptide chain of the protein upon its unfolding, which decreases the positive enthalpy of heat denaturation and increases the negative enthalpy of cold denaturation. The binding of urea considerably increases the partial heat capacity of the protein, especially in the denatured state. However, when corrected for the heat capacity effect of urea binding, the partial heat capacity of the denatured protein is close in magnitude to that expected for the unfolded polypeptide chain in aqueous solution without urea but only for temperatures below 10 degrees C. At higher temperatures, the heat capacity of the denatured protein is lower than that expected for the unfolded polypeptide chain. It appears that at temperatures above 10 degrees C not all the surface of the beta-lactoglobulin polypeptide chain is exposed to the solvent, even in the presence of 6 M urea; i.e., the denatured protein is not completely unfolded and unfolds only at temperatures lower than 10 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1988

Thermodynamic study of the apomyoglobin structure.

Sperm whale apomyoglobin has been studied thermodynamically in solutions with different pH and temperature by scanning microcalorimetry, viscosimetry, nuclear magnetic resonance and circular dichroism spectrometry, and by electrometric and calorimetric titration. It has been shown that apomyoglobin in solutions with pH close to neutral has a compact and unique spatial structure with an extended hydrophobic core. This structure is maximally stable at about 30 degrees C and breaks down reversibly both upon heating or cooling from this temperature. The process of breakdown of this structure is highly co-operative and can be regarded as a transition between two macroscopic states of protein, the native and denatured states. In contrast to the native state, which is specified by definite values of compactness and ellipticity, the compactness and ellipticity of the denatured state of apomyoglobin depend strongly on pH; with a decrease of pH below 4.0, these parameters gradually approach the values of the random coil.

Animals↗

PubMed1988

Cold denaturation of staphylococcal nuclease.

Denaturation of staphylococcal nuclease was studied in a temperature range from -7 to 70 degrees C by scanning microcalorimetry and spectropolarimetry. It was found that the native protein is maximally stable at about 20 degrees C and is denatured upon heating and cooling from this temperature. The heat and cold denaturation processes are approximated rather well by a two-state transition showing that the molecule is composed of a single cooperative system. The main difference between these two processes is in the sign of the enthalpy and entropy of denaturation: whereas the heat denaturation proceeds with increases in the enthalpy and entropy, the cold denaturation proceeds with decreases in both quantities. The inversion of the enthalpy sign occurs at about 15 degrees C in an acetate buffer, but this temperature can be raised by addition of urea to the solvent.

Calorimetry↗