High pressure stabilization of collagen structure.

Scanning microcalorimetry has been used to study heat denaturation of small es, Cyrillicollagen at high pressure. It has been demonstrated that an increase of the pressure by 200 MPa enlarges the structure stability by 6.8 degrees C. The pressure increase does not affect the cooperativity of transition and only slightly decreases its enthalpy. The changes of the partial specific volume of collagen as well as its isothermal compressibility and thermal expansibility during transition have been estimated. In contrast to denaturation of most globular proteins, denaturation of collagen proceeds with an increase of the partial specific volume at ambient pressure. Moreover, the absolute value of the collagen volume increment is distinctly greater than this in most globular proteins. The volume increment diminishes when the pressure increases due to the difference in the compressibility for folded and unfolded states. This effect is compensated to some extent by the differences in heat expansion. The volume increment alters its sign when the pressure reaches about 324+/-20 MPa and the temperature of denaturation grows to 49.7 degrees C. Further pressure growing destabilizes the collagen structure.

High pressure effect on the main transition from the ripple gel P'beta phase to the liquid crystal (Lalpha) phase in dipalmitoylphosphatidylcholine. Microcalorimetric study.

Scanning microcalorimetry has been used to study the high pressure effect on the main transition from the ripple gel P'(beta) phase to the liquid crystal (L(alpha)) phase in DPPC (dipalmitoylphosphatidylcholine). It has been demonstrated that an increase of the pressure by 200 MPa shifts the transition to higher temperatures by 36.4 degrees. The pressure increase does not affect the cooperativity of transition but reduces noticeably its enthalpy. The changes of the molar partial volume, isothermal compressibility as well as volume thermal expansibility during transition in DPPC suspension have been estimated. It has been shown that monovalent ions (Na(+), Cl(-)) in solution slightly affect the main thermodynamic parameters of the transition. Calcium ions significantly decrease distinction in compressibility and thermal expansibility between liquid-crystal and ripple gel phases of lipid suspension, which in its turn reflects less difference in their volume fluctuations.