Product-retardation and -activation of catalytic hydrolysis by phospholipase D in small unilamellar vesicles of egg yolk phosphatidylcholine

 We evaluated the hydrolysis of egg yolk phosphatidylcholine (PC) by phospholipase D from Streptomyces chromofuscus (PLD) in small unilamellar vesicles (SUV) in presence of 50 μM Ca²⁺. After initial choline production (hydrolysis of 1.5% of the PC at the outer leaflets of the vesicle bilayers), the hydrolysis was reduced to 5% of the initial velocity. The kinetic behavior in SUV of premixed PC and a low percentage of the hydrolysis product, phosphatidic acid (PA), was similar to that of PC SUV. The reduced velocity disappeared when the membrane structure was disintegrated by means of a nonionic surfactant. In the retardation phase, the partially hydrolyzed vesicles (postsubstrates) had much higher affinity for PLD than fresh PC SUV. These results indicated that small clusters of the product, PA, at the vesicle surface were responsible for the reduced velocity of hydrolysis. The initial velocity increased in a biphasic manner with the substrate concentration. At a PC concentration range up to 4 mM, the experimental data fit Michaelis–Menten kinetics. At concentrations above 6 mM, the velocity again markedly increased. Negatively charged mixed vesicles of PC and PA did not have such kinetics. Furthermore, adding PC SUV to the postsubstrates, where the fraction of free PLD was less than 0.05, induced steep choline production. These results showed that PLD bound to vesicles had higher activity than free PLD. We speculated that PLD bound to vesicles collided with and was directly transferred to PC SUV when the fraction of free PLD in aqueous medium was very small. Received: 5 November 1996 Accepted: 26 February 1997     

Dynamics and thermodynamics of dimerization of parallel G-quadruplexed DNA formed from d(TTAGn) (n=3-5)

Parallel G-quadruplexes formed from oligonucleotide sequences, d(TTAGn), where n = 3-5, have been shown to form a dimer through end-to-end stacking of 3'-terminal G-tetrads. The monomers and dimers of the G-quadruplexes are in dynamic equilibrium with an exchange rate of approximately 1 s-1. A thermodynamic study demonstrated that the dimerization of the G-quadruplexes is largely enthalpic in origin.     

Application of Hot Press Sintering to Na2O-B2O3-SiO2 Gels Containing Quantum Dots for Lowering of Densification Temperature

Na₂O-B₂O₃-SiO₂ (NBS) gels containing a large amount of CdS quantum-dots (10 wt%) were densified using the hot press (HP) sintering method. By HP treatment, full-densification temperature could be lowered by about 40°C than that of the normal non-pressing (NP) heat treatment. Exciton absorption of CdS quantum-dots in HP-sample showed a large blue shift compared with that in the NP sample, and the size-distribution of CdS dots remained very sharp, with a mean particle diameter d = 3.66 nm and a standard deviation of = 0.72. HP pressure had a large effect on the reduction of sintering temperature and time, resulting in the suppression of the aggregation and growth of CdS quantum-dots in NBS glasses.     

Grinding-induced equimolar complex formation between thiourea and ethenzamide

We prepared and characterized a grinding-induced equimolar complex of thiourea with ethenzamide. When thiourea and ethenzamide were co-ground at a molar ratio of 3 : 1, new powder X-ray diffraction (PXRD) peaks were observed in addition to PXRD peaks of thiourea crystals. The optimum stoichiometry of the new structure was confirmed as 1 : 1 mol/mol. Effect of grinding time on the thiourea-ethenzamide equimolar complex formation was investigated by using PXRD, differential scanning calorimetry and Fourier transform infrared spectroscopy. The equimolar crystal structure was confirmed by X-ray diffraction measurements of the single crystal which was recrystallized from ethanol. It was found that the intermolecular hydrogen bond formations between thiourea and ethenzamide molecules contributed to the equimolar complex formation. The complex formation was not observed in the cases where benzamide, salicylamide or 3-ethoxybenzamide was co-ground with thiourea. 2-Alcoxyl benzamide structures should be required for the grinding-induced equimolar complex formation with thiourea.     

Integration of gene amplification and capillary gel electrophoresis on a polydimethylsiloxane-glass hybrid microchip

We report on the development of a hybrid polydimethylsiloxane (PDMS)-glass microchip for genetic analysis by functional integration of polymerase chain reaction (PCR) and capillary gel electrophoresis (CGE), and on related temperature control systems for PCR on a PDMS-glass hybrid microchip. The microchip was produced by molding PDMS against a microfabricated master with comparatively simple and inexpensive methods. PCR was successfully carried out on the PDMS-glass hybrid microchip with 500 bp target of lambdaDNA and the amplified gene was subsequently analyzed by CGE on the same PDMS-glass microchip. The chip could be considered as an inexpensive single-use apparatus compared to glass or silicon-made microchips for the same purpose.     

Scope and limitations of chiral B-

A new chiral oxazaborolidine catalyst was prepared in situ from 3, 5-bis(trifluoromethyl)phenylboron dichloride and N-(p-toluenesulfonyl)-(S)-tryptophan. This catalyst is much more active than Corey's original catalyst for the Mukaiyama aldol reaction of aldehydes with silyl enol ethers. The observed syn selectivities and re-face attack of silyl enol ethers on carbonyl carbon of aldehydes imply that the extended-transition state model is applicable.     

The application of multivariate analysis to the radioallergosorbent test (RAST)

Multivariate statistical analyses using principal component analyses (PCA) and Mahalanobis' method were applied to the quality control of radioallergosorbent test (RAST). Mites and foods allergen were analyzed by PCA method, and foods allergen were analyzed by Mahalanobis' method. The vast differences in the distribution on titers among the mites and the foods were observed. To evaluate the results of a test and the quality of kits for test statistically, it should be better to use multivariate analyses such as PCA or Mahalanobis' method.     

Kinetic study of ion exchange reaction between lysozyme and carboxymethyl Sephadex C-25

The ion-exchange reaction of lysozyme with carboxymethyl Sephadex C-25 was followed by conductivity change as a function of time just after the rapid mixing of the protein solution with the Sephadex suspension. A single relaxation process was observed; the conductivity increased exponentially with time in the 100 s scale. In this process, protons were released from the Sephadex C-25 in the same time scale. The relaxation process slowed down with an increase in the lysozyme concentration, but it quickened upon the addition of HCl. On the other hand, the potential on the Sephadex C-25 surface changed from a negative value to a positive one with an increase in the amount of lysozyme adsorbed on the surface. On the basis of these data, the relaxation process was attributed to the ion-exchange reaction of lysozyme with several protons of carboxymethyl groups of the Sephadex.     

Radiological status of Rongelap Island in 1999

A radiological survey and whole body counting of ¹³⁷Cs were carried out in Rongelap Island (main island) of Rongelap Atoll in July 1999. The maximum values of ¹³⁷Cs contamination and of g-ray dose rate were 39 kBq/m² and 0.033 mSv/h, respectively. The maximum a and b gross counting rates on the surface of ground were 1 cpm and 182 cpm in active area of 72 cm², respectively. Activity of ^239,240Pu for soil was 80 Bq/kg in the top 5 cm and aerial deposition was 3.4 kBq/m² in Rongelap Island in 1999. The body burden of ¹³⁷Cs was observed to be 27±11 Bq/kg for 6 workers. Assessment of external and internal annual doses (0.1 and 0.07 mSv/y) indicates that as of 1999 there is no large risk to the inhabitants of Rongelap Island from a radiological point of view. The radiological status of Rongelap Island, which was severely contaminated by the radiological fallouts of nuclear testings carried out in 1954, has improved year by year as shown by the decrease of ¹³⁷Cs. The effective halftime of ¹³⁷Cs, which is estimated to be 6.6 y is much shorter than the physical half-life of ¹³⁷Cs. Radioactive contamination in Kaballe Island, (a part of the northern islands used for farming) which is located 25 km northeast of Rongelap Island, was still high in 1999. One site nearby a beach was highly contaminated with ¹³⁷Cs, where the maximum activity of ¹³⁷Cs was 3.4 MBq/m², a-ray of 2 cpm, b-ray of 1205 cpm and g-ray of 0.73 mSv/h. Activity of ^239,240Pu in soil (n = 1) was 294 Bq/kg (top 5 cm) and 16 kBq/m².     

Convergent synthesis of polycyclic ethers via the intramolecular allylation of alpha-acetoxy ethers and subsequent ring-closing metathesis

The Lewis acid mediated reaction of alpha-acetoxy ethers 15-22 gave the corresponding cyclized products 23, 25, 27, 29, 31, 32, 34, and 36 in good yields with high stereoselectivities. Those cyclized products were subjected to ring-closing metathesis to afford the polycyclic ethers 38-42, 44, and 45 in good yields. The usefulness of the present methodology was demonstrated by the convergent synthesis of the CDEF ring system of brevetoxin B (1) and the CDEFG ring system of gambierol (2).