Model biological microemulsions: Part I--Phase behaviour and physicochemical properties of cholesteryl benzoate and sodium deoxycholate contained microemulsions

Phase behaviour and some physicochemical properties of cholesteryl benzoate-contained microemulsions of xylene and heptane with water using sodium deoxycholate and butan-1-ol as surfactant and co-surfactant respectively have been studied. While the microemulsion area of xylene depends insignificantly on the surfactant/co-surfactant ratio, that of heptane shows appreciable dependence. At surfactant + co-surfactant percentage of 50 or above, both the systems become oil continuous. With respect to time and temperature, the microemulsion systems have been found to be very stable. At low percentage of water, the xylene system is considerably viscous; that of heptane is less viscous but shows viscosity maximum at 45% water. Cholesterol in xylene has given greater viscosity than cholesteryl benzoate. The equivalent conductance of both the systems increase with increasing water content and the values are comparable. Unlike normal electrolyte solutions, the products of equivalent conductance and viscosity (the Walden product) sharply rise with increased water content, which suggests a special mechanism of conduction via 'channel' formation. The overall rigidity of the microemulsions is suggested by their lower specific volumes and compressibilities at all compositions. The excess specific volumes and excess compressibilities at different percentages of water are presented.     

Enzymes and microemulsions. Activity and kinetic properties of liver alcohol dehydrogenase in ionic water-in-oil microemulsions

The activity and the kinetic properties of horse liver alcohol dehydrogenase have been studied in water-in-oil microemulsions containing sodium dodecyl sulfate (SDS) or hexadecyl trimethylammonium bromide (CTAB), 1-butanol or 1-pentanol or 1-hexanol or t-butanol, water and cyclohexane alone or with octane. In the anionic microemulsions (i.e. containing sodium dodecyl sulfate), the enzyme quickly lost its activity, but was efficiently protected by the coenzyme and some adenine nucleotides. In the cationic microemulsions (i.e. containing hexadecyl trimethylammonium bromide), the enzyme activity was more stable and with higher alcohols was stable for at least 20 min. The Michaelis constant of NAD+ calculated with respect to the water content was nearly constant and higher than in water. The maximum velocity in anionic microemulsions depends on the water content whereas in cationic microemulsions, the maximum velocity did not show a clear dependence on the water content and was close to the maximum velocity found in water. The pH dependence of Km and Vmax in these microemulsions was similar to that observed in water. The kinetic data for a hydrophobic substrate, cinnamyl alcohol, showed that this alcohol partitions between the pseudo-phases and thus the apparent Michaelis constant and the concentration at which substrate-excess inhibition appeared were increased. The catalytic properties of the enzyme in microemulsions were illustrated by the preparative reduction of cinnamaldehyde with cofactor recycling. The rate determination of NAD+ reduction and of 1-butanol/cinnamaldehyde redox reaction showed that at low water content (2.8%), the NAD+ reduction rate was close to zero whereas the redox reaction rate was about half of the rate at higher water content. Probably at low water content the coenzyme binding-dissociation rates are reduced much more than the binding-dissociation rates of the substrates and the rates of the ternary complex interconversion. The cationic microemulsions seemed to be very favorable medium for enzyme activity, the tetraalkyl ammonium surfactant causing less denaturation than the anionic detergent dodecyl sulfate.     

Biological characteristics of a type I restriction-modification system in Staphylococcus aureus.

Two restriction-modification systems, S1 and S2, are present in Staphylococcus aureus RN450 (S. Iordanescu and M. Surdeanu, J. Gen. Microbiol., 96:277-281, 1976). System S2 affects phage multiplication after both infection and transfection. Unmodified plasmid and chromosomal DNAs are also not expressed following transduction and transformation into a restrictive host. Restricted phages are, however, capable of conferring phage-mediated competence, although the state of competence does not affect the restriction-modification system. The restricting activity of system S2 is inactivated by heat treatment of the cells. An enzymatic activity that restricts unmodified phage DNA in the presence of ATP, Mg2+, and S-adenosylmethionine was recovered from cell-free extracts of a strain RN450 derivative.     

The formation and characteristics of China's existing system

Conclusion To sum up, the character of China's existing system is basically all-embracing totalitarianism formed by the combination of the old tradition of feudal-despotism and the new tradition of Stalinism. This system is the basic source of all the social evils in China.The ultimate aim of the democratic movement is to transform the old, allembracing totalitarian system and to establish a democratic, free, humane, and rational new system. The present ruling group is the beneficiary and defender of the existing system. The contradictions and conflicts between reformers who want to transform the old system and the hardliners who want to protect the old system formed the crux of the struggle of the 1989 democratic movement. Because the democratic movement lacked preparation in theory, organization, tactics and strategy, and because the ruling group controls the means of dictatorship — especially the army —military force was used to suppress the democratic movement with brutal bloodshed. In order to promote the democratic movement, we should sum up some lessons and experiences. First, we should study in depth the existing system and oppose feudaldespotism and Stalinism through effective propaganda and education. Second, we should arouse the democratic consciousness of the broad masses of the people, uniting with them and the healthy elements inside the Party, government, and army to struggle for the smashing of the old system and the establishment of a new system.Su Shaozhi is former Director of the Institute for the Study of Marxism-Leninism and Mao Zedong Thought, Chinese Academy of Social Sciences, Beijing, and currently Visiting Professor at the Bradley Institute for Democracy and Public Values, Marquette University, Milwaukee, Wisconsin     

Biological properties of selenobiotin.

Selenobiotin is an excellent growth factor, as efficient as biotin in supporting the growth of biotin requiring microorganisms. It is incorporated in carboxylases leading to active “selenocarboxylases”. With E. Coli, the activity of the selenoacetyl CoA carboxylase is very similar to that of the normal enzyme.     

S-Nitrosothiols: cellular formation and transport

This review will focus on the transport and intracellular formation of S-nitrosothiols in cell culture models. The major points made in this article are: (1) S-Nitrosothiols are actively metabolized by cells. (2) S-Nitrosothiols affect cells in ways distinctly different from those of nitric oxide and can act through mechanisms that do not involve the intermediacy of nitric oxide. (3) Some S-nitrosothiols (S-nitrosocysteine, S-nitrosohomocysteine) can be taken up into cells via amino acid transport system L, whereas others (S-nitrosoglutathione, S-nitroso-N-acetylpenicillamine) are not directly transported, but require the presence of cysteine and/or cystine before the nitroso functional group is transported. (4) Proteomic detection of intracellular S-nitrosothiols is currently possible only if cells are loaded with high levels of S-nitrosothiols, and methodological advances are required in order to examine the S-nitrosated proteome after exposure of cells to physiological levels of nitric oxide.     

一株从临床分离的奥默儿玉氏酵母的生物学特征及其致病毒力相关特性

奥默儿玉氏酵母Kodamaea ohmeri已经成为一种重要的新兴人类酵母病原体。本文利用形态学和ITS序列分析鉴定分离自患者腹水的临床菌株3873为K. ohmeri。5-氟胞嘧啶、两性霉素B、氟康唑、伊曲康唑和伏立康对菌株3873的MIC值分别为≤4、≤0.5、≤4、≤0.125和≤0.6 mg/L。菌株3873在血清诱导下发育出假菌丝,无法形成真菌丝,且在微需氧条件下侵入能力强;最适生长温度和pH分别为37℃和7.0,在此条件下细胞表面疏水性也最高;采用试管法和微平板法静置培养48h形成大量生物膜;在体外培养条件下,对刚果红、羟基脲和H₂O₂具有一定的耐受能力,对NaCl试剂较为敏感。本研究有助于更好地了解K.ohmeri的基本生物学特征和与其毒力相关的特性。     

六盘山翠金小蜂生物学特性的研究

六盘山翠金小蜂Tritneptis sp.是华北落叶松人工林主要食叶害虫落叶松红腹叶蜂Pristiphora erichsonii Hartig茧期的体外复寄生性天敌。对该蜂的生物学特性研究表明,该蜂在宁夏六盘山1年2代,以幼虫在寄主茧内越冬,翌年4月中旬开始活动取食,5月中旬开始化蛹,成蜂从6月中旬开始羽化,每头虫茧平均出蜂6.14头,雌雄比1.79∶1,雌蜂6月下旬开始产卵,一只雌蜂一生可在12.2头寄主虫茧上产卵,第1代寄生蜂幼虫7月上旬开始孵化并吸食寄主营养发育,7月下旬开始化蛹,8月上旬开始羽化并交尾、产卵寄生。该蜂体型较大,对寄主跟随性强,无重寄生天敌,自然寄生率7.3%～33.6%,是一种优良天敌寄生蜂。     

Fibrillar beta-lactoglobulin gels: Part 1. Fibril formation and structure

As a prelude to experimental and theoretical work on the mechanical properties of fibrillar beta-lactoglobulin gels, this paper reports the structural characterization of beta-lactoglobulin fibrils by electron and atomic force microscopy (AFM), infrared and Raman spectroscopy, and powder X-ray diffraction. Aggregates formed by incubation of beta-lactoglobulin in various alcohol-water mixtures at pH 2, and in water-trifluoroethanol (TFE) at pH 7, were found to be wormlike (approximately 7 nm in width and <500 nm in length), with a "string-of-beads" appearance. Longer (approximately 7 nm in width, and >1 microm in length), smoother, and seemingly stiffer fibrils formed on heating aqueous beta-lactoglobulin solutions at pH 2 and low ionic strength, although there was little evidence for the higher-order structures common in most amyloid-forming systems. Time-lapse AFM also revealed differences in the formation of these two fibril types: thermally induced aggregation occurring more cooperatively, in keeping with a nucleation and growth process. Only short stiff-rods (<20 nm in length) formed on heating beta-lactoglobulin at pH 7, and only complex three-dimensional "amorphous"aggregates in alcohols other than TFE at this pH. Studies of all of the pH 2 fibrils from beta-lactoglobulin, by Raman and infrared spectroscopy confirmed beta-sheet as mediating the aggregation process. Interestingly, however, some evidence for de novo helix formation for the solvent-induced systems was obtained, although it remains to be seen whether this is actually incorporated into the fibril-structure. In contrast to other amyloid systems, X-ray powder diffraction provided no evidence for extensive repeating "crystalline" structures for any of the pH 2 beta-lactoglobulin fibrils. In relation to amyloid, the lactoglobulin fibrils bear more resemblance to protofilaments than to higher-order fibril structures, these latter appearing more convincingly for thermally induced insulin fibrils (pH 2) also included in the AFM study.     

Synthesis and transport characteristics of photoaffinity probes for the hepatocyte bile acid transport system

In an effort to characterize the hepatocyte bile acid transport system, a photoreactive derivative of taurocholate, (7,7-azo-3 alpha,12 alpha-dihydroxy-5 beta-cholan-24-oyl)-2-aminoethanesulfonic acid (7-ADTC) has been synthesized and its transport properties compared to those of the natural substrate. Both the bile acid and its synthetic analog were shown to be transported against an electrochemical gradient as well as a chemical gradient. Transport as a function of concentration and the presence of sodium indicated that both substrates were taken up by a sodium-dependent and a sodium-independent route. Taurocholate had Km values of 26 and 57 microM and Vmax values of 0.77 and 0.15 nmol/mg of protein/min, respectively. In comparison, 7-ADTC had very similar kinetic properties with Km values of 25 and 31 microM and Vmax values of 1.14 and 0.27 nmol/mg of protein/min. Each compound was shown to inhibit competitively the transport of the other, suggesting that these substrates utilized a common membrane carrier. The transport properties of the photoreactive anion transport inhibitor, N-(4-azido-2-nitrophenyl)-2-aminoethylsulfonate (NAP-taurine) were also characterized in the hepatocyte system. Transport occurred via a sodium-dependent and a sodium-independent route with Km values of 210 and 555 microM and Vmax values of 0.57 and 1.62 nmol/mg of protein/min. As in the case of 7-ADTC, NAP-taurine and taurocholate were also shown to be mutual competitive inhibitors. In the absence of light, 7-ADTC was a reversible inhibitor of taurocholate uptake. Upon irradiation, irreversible photoinactivation of the taurocholate uptake system was observed. These results indicate that 7-ADTC and NAP-taurine can be utilized as photoaffinity probes for the identification of the bile acid carrier protein(s) in hepatocyte plasma membranes.     

一株产蓝色素菌株生物学特性及色素基本性质的研究

对一株从土壤中筛选的产蓝色素链霉菌-ZLT菌株进行了生物学特性和色素基本特性的研究。根据其形态、培养特征和生理生化特性分析,该产蓝色素菌株为链霉菌属,命名为链霉菌-ZLT。与现有报道的放线菌蓝色素相比,该色素纯度较高,无毒副作用,初步认为该色素为一种新的天然蓝色素。     

Guar gum derivatives. Part I: Preparation and properties

O-(2-Hydroxyethyl), O-(2-hydroxypropyl) and O-carboxymethyl derivatives of guar gum have been prepared under different experimental conditions. Several properties such as moisture regain, rate of hydration, solubility, viscosity and rheology of these derivatives have been studied. The properties depend upon polysaccharide chain length, and the nature and degree of chemical modification. The effect of alkali and alkaline hydrogen peroxide on the properties of guar gum have also been studied.     

The Cu(II)-fluconazole complex revisited. Part I: Structural characteristics of the system

Protonation equilibria and Cu(II) binding processes by an antifungal agent fluconazole, α-(2,4-difluorophenyl)-α-(1H-1,2,4-triazol-1-yl-methyl)-1H-1,2,4-triazole-1-ethanol, were studied using the UV-Vis, EPR and NMR spectroscopic techniques. The protonation constant of fluconazole was determined from NMR titration and attributed to N4′ nitrogen atoms using the DFT methods. The spectroscopic data suggest that at pH as low as 0.4 the first complex is formed, in which one or two Cu(II) ions are bound to one of the nitrogen atoms (N4′) from triazole rings. Above pH 1.5 each Cu(II) ion is surrounded by two nitrogen atoms (also N4′) from two different ligand molecules, forming primary monomeric complexes and above pH = 5, both dimeric or oligomeric species occur, which is well registered by the EPR technique.The mixture of Cu(NO₃)₂ with fluconazole in a 1:1 molar ratio in a water (pH = 4.5)/ethanol solution gave crystals of [Cu₂(H₂O){(C₆H₃-2,4-F₂)(CH₂N₃C₂H₂)₂C-OH}{(C₆H₃-2,4-F₂)(CH₂N₃C₂H₂)₂C-O}(NO₃)](NO₃)₂·9(H₂O). This complex is the first example of a cupric 3D polymeric structure with a fluconazole ligand coordinated via both N2′ and N4′ atoms from the same triazole rings. At higher pH values, we obtained a binuclear complex [Cu₂(L)₂(H₂O)₂(NO₃)₂], in which the copper(II) atoms were bridged by the oxygen atoms of the deprotonated OH group of fluconazole.The hypothetical oxidative properties of this system were also examined, however it failed to generate either reactive oxygen species or DNA scission products.     

Physiological and regulatory properties of the general amino acid transport system of Neurospora crassa.

The fundamental properties of the general amino acid transport system of Neurospora crassa were investigated in the conidial stage of the life cycle. The transport activity was found to be under genetic control, and an isogenic set of mutants deficient for the neutral, basic, or general amino acid transport systems and combinations thereof was constructed and used for analyzing the properties specific to the general permease. Amino acid transport by this system was found to be a carrier-mediated active process with broad specificity for the neutral and basic amino acids. Kinetic analysis revealed that a common binding site functioned to transport both neutral and basic amino acids and that the permease had a high affinity for its substrates. The kinetic parameters Km, Vmax, and Ki were defined for several substrates. Two modes of regulation were detected: substrate inhibition and ammonium repression. Activity of the general system was enhanced by the removal of ammonium ions from the incubation medium with a concomitant decline in either neutral or basic permease activity, suggesting that a common component exists between the neutral and the general systems and between the basic and the general systems.