Microorganisms have potential capacities to adapt to environmental changes to a certain extent. As extreme cases, a variety of microorganisms such as thermophiles, psychrophiles, acidophiles, alkalophiles and halophiles have been isolated from the natural environments. The structure and function of cell membranes play essential roles to cope with an environmental stress. We studied the modes of adaptations of a slightly halophilic marine bacterium, Vibrio alginolyticus, to salt concentrations and pH changes. As a response to osmotic stress, the cells accumulate K⁺, glutamate and proline as osmoprotectants. Except for extreme halophiles (archaebacteria), the mode of osmotic adaptation of halophilic bacteria was very similar to those of nonhalophilic bacteria. The adaptation to the changes in external pH is performed by maintaining the intracellular pH nearly constant. In V. alginolyticus, K⁺/H⁺ antiporter functioned as a “pH regulator” over the pH range from 6.0 to 9.0. Marine bacteria are unique in having the respiratory chain-driven Na⁺ pump. The site of energy coupling was assigned to the Na⁺_dependent NADH-quinone reductase segment, which was composed of three subunits (α, β, γ) and contained FAD (β) and FMN (α) as cofactors. Since the respiratory chain of marine bacteria also generates proton-motive force, both Na⁺ and H⁺ are utilized as energy-coupling ions. Energy coupling by the Na⁺ circulation is of great advantage to the energetics of marine bacteria. These examples represent the importance of membrane functions in the microbial adaptations to environmental changes.

View full abstract

One of the important roles of plasma membranes is a site of molecular recognitions accepting external informations and transducing particular signals. Recent works show that lipids as well as proteins are involved in molecular recognition and may function such as receptors. In this review, we present several examples and studies about the roles of lipids in molecular recognition. First, we described the specific roles of phospholipids such as recognition sites for antibiotics and perforin. Next, we referred the roles of glycolipids in molecular recognition and in cell-cell communication. For example, component of glycolipids are changed during cell growth, development and differentiation. On the contrary, cells cultivated in the presence of particular ganglioside were differentiated. The molecules which recognize determinant sugar structure on cell surface have not been identified. Recently, it is reported that cell surface sugar chains containing Le_x structure have affinity for another Le_x of other cells, suggesting that intercellular recognition is performed between sugar structures. Last part, we mentioned about the recognition of various unspecified chemical substances by chemosensory cells, taste cells and olfactory cells. At least, some bitter substances and odors could interact with liposomes without membrane proteins, suggesting that lipid bilayer is responsible for the first recognition site for such substances.

View full abstract

We reviewed a sensing system and mechanism of bitter and odorous compound by using a lipid-coated quartz-crystal microbalance. Strength of bitter taste and odorant can be explained by the adsorption amount to a lipid matrix : the stronger bitter or odorous compound absorbs into the lipid membrane with the larger amount. This adsorption behavior can be explained by hydrophobicity and molecular shape of additives : the more hydrophobic and the more slender molecule absorbs into the lipid matrix with the larger amount.These adsorption behaviors can be applied for other bioactive compounds such as anesthetics, antibiotics, and hydrophobic drugs.

View full abstract

The purpose of this work was to develop a standard analytical technique for determining solute concentrations in a retention characterization of sheet ultrafiltration (UF) membranes. Three cells of different shape and area were used. And two different UF membranes were evaluated with three polyethylene glycols (PEG) of different average molecular weights, specifically 7500, 20000, and 50000. The experiments were done under the following conditions : 10-20kPa of transmembrane pressure (TMP), 0.024-0.24m/s linear velocity (u), and 100-300mg/l feed concentration (C). The solutions with a single molecular weight solute were analyzed by a TOC analyzer, and a GPC analyzer was used for mixed molecular weight solutions.
It was observed that the shape of the cells did not influence either the molecular weight cut-off or the mass transfer coefficient as calculated by Leveque's equation.

View full abstract

Two-dimensional microcrystal-like domain formation in a monolayer of 2-octadecyl-7, 7, 8, 8-tetracyanoquinodimehane was electron microscopically visualized. The electron microscopic examinations suggested that the co-existence of microcrystals and relatively fluid condensed form (s) in the so-called solid state of monolayer on an aqueous subphase. When the monolayer deposition was conducted at a surface pressure higher than the so-called collapsing pressure and its electron micrograph was obtained, no significant collapsed pattern could be visualized on the electron microscopic scale. On the basis of our finding, we assume that the collapsing pressure tentatively called in this study might not be the so-called collapsing pressure. Further monolayer compression might permit the formation of a large two-dimensional crystal-like domain in monolayer on the aqueous subphase.

View full abstract

The acceleration effects of surfactants on the reduction of dichlorophenol indophenol (DPIP) with diphenylcarbazide as a reductant were investigated. The surfactants used were acidic, cationic, zwitterionic and nonionic species. Each surfactant showed its maximum acceleration effect at the concentration approximate to its CMC. Zwitterionic sulfobetaine-14 apparently accelerated the reaction by 32 times at pH 5.5, which was the largest value among those given by the surfactants tested. Soybean asolectin also showed the acceleration activity irrespectively whether it was sonicated or not. From absorption change of DPIP in the presence of surfactants and partition efficiencies of the reactants in n-dodecane, the mechanism of the acceleration was discussed relating to the location and microenvironmental pH of the reactants.

View full abstract