Transport of monooleoylglycerol mediated by bile salt micelles across porous membranes

In order to study how the bile salts and lipids behave in the vicinity of microvillus, the transport properties of a sodium salt of deoxycholic acid (NaDC) and its mixture with monooleoylglycerol (MO) through artificial membranes were investigated in 0.15 M NaCl saline solution at 37°C.The hydrodynamic radius of MO-solubilized micelles was estimated to be approximately 17–20 Å from the transport study. The thermodynamically stable MO-NaDC mixed micelles formed above critical micelle concentration in the higher region of mole fraction of NaDC in the mixture (X _NaDC>ca. 0.6), can behave as a single species in transport process and freely pass through the porous membranes of both pore sizes, 0.01 m and 0.1 m.The permeabilities of MO-NaDC mixed micelles are large compared with those of pure NaDC micelles. MO molecules solubilized may probably enhance the interaction between MO and NaDC molecules by better contacting with the respective hydrophobic groups in a mixed micelle (the flexible structure of MO molecule enables it), and in this situation, the smaller micelles compared with those of pure NaDC must be more favorable.     

Solubilization and precipitation of cholesterol in aqueous solution of bile salts and their mixtures

Solubilization of cholesterol by mixed micelles of sodium chenodeoxycholate with sodium ursodeoxycholate was investigated in carbonate-tetraborate buffer (Kolthoff) solution at pH 10 and 37°C. It was found that the mixing of the two bile salts gives a negatively synergetic effect on solubilization of cholesterol. The solubilizing power of bile salts for cholesterol was remarkably influenced with the change in mole fraction of sodium ursodeoxycholate (X _UDC).The behavior of bile salt solutions saturated with cholesterol was examined by measuring the surface tension. Two break points were observed in the curves of surface tension vs. concentration. The break points seem to correspond to a CMC in the absence of solubilized cholesterol and another CMC in the presence of solubilized cholesterol inside bile salt micelle.     

Spin and fluorescence label studies on bile salt micelles

The interior structure of micelles formed by bile salts, which differ in the number and location of the hydroxyl groups attached to the steroid nucleus, was studied by the spin label and fluorescence label methods. The results show that the interior structure of micelles formed by bile salts possessing two hydroxyl groups is more rigid than that of micelles formed by trihydroxy bile salts regardless of the terminal hydrophilic group. Even in the case of dihydroxy bile salts possessing two hydroxyl groups in the same location, the interior structures of their micelles are different from each other depending on the orientation of their hydroxyl groups. It is considered that hydroxyl groups as well as the terminal hydrophilic group play an important role in the micellar formation of bile salts.     

Automatic polymerase chain reaction product detection system for food safety monitoring using zinc finger protein fused to luciferase

An automatic polymerase chain reaction (PCR) product detection system for food safety monitoring using zinc finger (ZF) protein fused to luciferase was developed. ZF protein fused to luciferase specifically binds to target double stranded DNA sequence and has luciferase enzymatic activity. Therefore, PCR products that comprise ZF protein recognition sequence can be detected by measuring the luciferase activity of the fusion protein. We previously reported that PCR products from Legionella pneumophila and Escherichia coli (E. coli) O157 genomic DNA were detected by Zif268, a natural ZF protein, fused to luciferase. In this study, Zif268–luciferase was applied to detect the presence of Salmonella and coliforms. Moreover, an artificial zinc finger protein (B2) fused to luciferase was constructed for a Norovirus detection system. In the luciferase activity detection assay, several bound/free separation process is required. Therefore, an analyzer that automatically performed the bound/free separation process was developed to detect PCR products using the ZF–luciferase fusion protein. By means of the automatic analyzer with ZF–luciferase fusion protein, target pathogenic genomes were specifically detected in the presence of other pathogenic genomes. Moreover, we succeeded in the detection of 10 copies of E. coli BL21 without extraction of genomic DNA by the automatic analyzer and E. coli was detected with a logarithmic dependency in the range of 1.0 × 10 to 1.0 × 10⁶ copies.     

Transport behavior of four bile salt micelles and cholesterol solubilized by their micelles across porous membrane

 The transport behavior of bile salts (BSs) solubilizing cholesterol (Ch) or none across an artificial membrane was investigated for sodium salts of deoxycholic acid (NaDC), chenodeoxycholic acid (NaCDC), ursodeoxycholic acid (NaUDC) and cholic acid (NaC) in tetraborate–carbonate buffer solution at pH 10.0 and 37 °C. The study demonstrated that the surfactant properties such as critical micellization concentration (CMC) and micellar size or diffusion coefficient were determinable from the flux or permeability measurements. The comparison among the respective pure systems of BSs led to a conclusion that the micellar size was in the order of NaDC>NaCDC>NaUDC>NaC and determined CMC values were in agreement with those in literature. The magnitude of solubilizing power (capacity) of BS for Ch was found to decrease in the order of NaDC>NaCDC>NaC>NaUDC; this order is in accordance with that of the empirical hydrophobicity index. The hydrodynamic radii for the singly dispersed species and the micellar species of the respective BSs and of Ch-solubilizing micelles were estimated from the permeability data; the radii of the Ch-solubilizing micelles are approximately 12–15 Å and interestingly, smaller than those of the respective BS alone micelles ranging from 14 to 22 Å. Received: 15 April 1997 Accepted: 25 July 1997