High pressure treatment of microbial cells and plant and animal tissues at 100-400 MPa solubilizes cellular compounds such as metals, amino acids, and proteins, permeates extra-cellular compounds such as salts into cells and tissues, and causes hemolysis. After the pressure treatment, electron microscopic observation of yeast cells and biochemical analysis of animal tissues reveal a significant membrane breakage of nuclei, lysosomes, and vacuoles in addition to light cell membrane and cell wall damage. To understand these observed phenomena at the molecular level, we studied functional and structural changes of the membrane-bound Na+, K+-ATPase under increasing high pressure (in situ observation), and reached an interesting conclusion that contact faces of lipid and membrane-penetrating protein surfaces are reversibly separated to produce tunnels or holes at 100-250 MPa, followed by disordered breakdown of the membrane system including protein denaturation at 300 MPa or higher. This conclusion is well supported by the phase transition of the lipid bilayer membrane.
To determine the effect of high-pressure-freezing on quality, carrots and tofu (soybean curd) were frozen at 100 MPa (ice I), 200 MPa (liquid phase), 340 MPa (ice III), 400, 500, 600 MPa (ice V) or 700 MPa (ice VI) at ca. -20 °C then thawed at atmospheric pressure. The texture and structure of these foods frozen at 200 ∼ 400 MPa improved in comparison to foods frozen at 0. 1 MPa (frozen in freezers at -20 °C, -30 °C or -80 °C) or 100, 600 and 700 MPa. However, ice crystals were observed even in tofu frozen at 200 MPa ∼ 400 MPa. Therefore, tofu was also thawed at a high pressure and then the pressure was reduced. Texture and structure (pore size) of tofu frozen at 200∼400 MPa were the same as for unfrozen tofu. This indicated that phase transitions (ice VI → ice V → ice III → liquid → ice I) occurred during reduction of pressure at 20°C, during freezer storage or while thawing at 0. 1 MPa Thus, high-pressure freezing-thawing at 200∼400 MPa was effective in improving the quality of frozen foods.
Trehalose (α-D-Glucopyranosyl α-D-glucopyranoside) is one of the disaccharides and exists widely in animals, plants and bacteria. In this article, the role of trehalose in microbial cells was discussed from the point of view of their stress response: synthesis of heat shock proteins and trehalose, and the induction of stress tolerance. Further-more, an outline of the behavior of microbes under high pressure was also given. The concrete contents of the article are (1) effects of trehalose on thermotolerance of pressure-shocked yeast, (2) effects of temperature and pressure on the death rate of Lactobacillus casei and Escherichia coil, (3) properties and functions of trehalose, (4) extreme barotolerance of tardigrade, and (5) correlation of thermotolerance and barotolerance of yeast and the mean number of equatorial OH groups in sugar molecules.
Several baro (piezo) -philic microorganisms have been isolated from a deep-sea high hydrostatic pressure environment in our laboratory. The results of taxonomic studies showed that all of the barophile isolates belonged to Proteobacteria gamma-subgroup, and four novel species were identified. The moderately barophilic bacterium, Shewanella violacea strain DSS 12 was one of them, and this strain was able to grow from atmospheric pressure (0. 1 MPa) to 70 MPa conditions in the same way. Molecular mechanisms of pressure-regulation on gene expression in S. violacea were analyzed, and we identified particular DNA binding proteins that might be essentially important for pressure regulation. Atmospheric pressure adapted Escherichia coli that belonged to the same gamma-subgroup of the isolated barophilic species was also studied and we could observe the positive and negative effects on pressure regulation. Finally, we observed that hyper-thermophilic archaea could grow well under higher pressure conditions at higher temperatures. These results indicated that pressure could affect microorganisms' survival in several ways in such an environment.
Pressure studies on the bilayer phase transitions of phosphatidylcholines with various acyl chains are reviewed. Temperature-pressure phase diagrams of lipid bilayer membranes are shown. In addition to liquid crystal, ripple gel, and lamellar gel phases; the presence of a pressure-induced gel phase, i. e., the interdigitated gel phase was found. The minimum pressure for the interdigitation of lipid bilayers decreased with an increase in acyl chain length in a non-linear manner. Thermodynamic quantities for the main transition were non linear with respect to the acyl chain length. The effect of an unsaturated acyl chain on the phase behavior was also described.
The first high pressure study on a fast inorganic reaction was reported by Brower in 1968. Since then, various high pressure apparatus for the study of fast reactions in solution, such as high-pressure T-jump, P-jump, NMR, stopped-flow, etc., have been exploited with the increasing interest in the high pressure chemistry of fast inorganic reactions. In this review, after brief explanations of the apparatus and classification, the relation of activation volumes and complex formation and solvent exchange mechanisms of metal ions classified by the Langford and Gray classification, which is assigned on the basis of kinetic data at ambient pressure, is explained. Recent studies relevant to high pressure kinetics are also covered.