ESTERASES OF BAKER'S YEAST. III. THE ESTER/ACID RATIO IN MODEL SOLUTIONS

Ester/acid equilibria were studied in reaction mixtures containing ethyl alcohol, ethyl caprylate or caprylic acid, and baker's yeast or an esterase purified from baker's yeast in buffer. The equilibrium concentration of ethyl caprylate after an incubation of yeast or a yeast esterase preparation with caprylic acid was the same as in the case where yeast or esterase preparation was incubated with the ethyl caprylate. The equilibrium attained depends not only on the concentration of the ester and the alcohol but also on the pH, the final ester concentration remaining higher at low pH. It could be shown that yeast esterase is responsible for the hydrolysis or synthesis of the ester. At equilibrium the molar ratio of ethyl caprylate/caprylic acid is about the same as that found in fermentation solutions under the same conditions.     

THE ESTERASES OF BAKER'S YEAST. I. ACTIVITY AND LOCALIZATION IN THE YEAST CELL

The activity of esterase in baker's yeast cells and in cell fractions was estimated using 2-oxoglutaric acid diethyl ester, p-nitrophenyl acetate and α- and β-naphthyl acetate as substrates. The esterase hydrolysing 2-oxoglutaric acid ester was shown to be located inside the cell, both directly by an enzymic method and by indirect evidence. The activities of the esterases hydrolysing aryl esters were found to vary greatly with the different substrates and estimation methods used. The presence of esterase activity towards phenyl and naphthyl esters in both cell wall digests and sphaeroplast lysates confirms the localization of at least one esterase in both sides of the plasma membrane barrier. Depending on the method of evaluation, values between 80 and 40% of the total were obtained for the proportion of esterase activity located outside the plasma membrane, the most reliable values being about 50–65%.     

Development of bioactive food packaging materials using immobilised bacteriocins lacticin 3147 and nisaplin

Immobilisation of the bacteriocins nisin and lacticin 3147 to packaging materials was investigated. Stability of both cellulose-based bioactive inserts and anti-microbial polyethylene/polyamide pouches was examined over time. Anti-microbial activity against the indicator strain Lactococcus lactis subsp. lactis HP, in addition to Listeria innocua DPC 1770 and Staphylococcus aureus MMPR3 was observed for all bacteriocin-adsorbed materials. Activity retention of the inserts showed an initial decrease in the first week of storage but remained stable for the remaining 3 months of the trial. However, adsorption of lacticin 3147 to plastic film was unsuccessful, nisin bound well and the resulting film maintained its activity for 3-month period, both at room temperature and under refrigeration. When applied to food systems, the anti-microbial packaging reduced the population of lactic acid bacteria in sliced cheese and ham stored in modified atmosphere packaging (MAP) at refrigeration temperatures, thus extending the shelf life. Nisin-adsorbed bioactive inserts reduced levels of Listeria innocua by ≥2 log units in both products, and Staphylococcus aureus by 1.5 log units in cheese, and 2.8 log units in ham. Similar reductions were observed in cheese vacuum-packaged in nisin-adsorbed pouches.     

Effect of PEGylation on the stability of liposomes during nebulisation and in lung surfactant

Oral inhalation of anticancer drugs or drug delivery system is a novel therapeutic approach in the treatment of lung cancer and requires formulations which are sufficiently stabile during nebulisation and subsequent interaction with the surfactant lining of the lungs. In this study, we assessed the stability of plain and PEGylated transferrin-conjugated liposomes after nebulisation using two different nebulisers (i.e., air-jet and ultrasonic type). Furthermore, the integrity of the liposomal membranes was assessed after incubation in commercial lung surfactant solutions (Alveofact). All liposomal formulations showed no significant changes in their size after nebulisation, independent of the type of nebuliser or the liposomal formulation, respectively. However, PEGylation was of advantage when it came to interactions between liposomes and the surfactant lining of the lungs. PEGylated liposomes were significantly more stable and retained > 80% of their drug load over 48 h, which is more than sufficient time for the drug carriers to be taken up by transferrin receptor over-expressing cancer cells in the lung. In conclusion, PEGylated and plain Tf-conjugated liposomes are stable enough to undergo nebulisation in the course of an inhalational therapy, but PEG-stabilisation results in a higher degree of membrane integrity in lung surfactant.     

纳米技术在锂二次电池中的应用

对近几年来纳米技术在锂二次电池中的应用进行了综述。所用纳米技术包括溶胶 凝胶法、模板法、碳棒电弧法和机械研磨法等,制备的锂二次电池纳米材料包括正极、负极和其它材料。纳米正极材料包括氧化钴锂、氧化镍锂、氧化锰锂和钒的氧化物等,纳米负极材料包括碳材料、富勒烯、碳纳米管、氧化锡和金属负极材料等,其它纳米材料包括聚合物电解质和导电剂。这些纳米材料的电化学性能较一般方法制备的材料有明显的提高,但是目前在锂二次电池领域对纳米技术的理论研究还有待于深入。随着纳米技术的不断发展,微型锂二次电池的诞生为期不远。     

NAD(P)H:Quinone Oxidoreductase 1 (NQO1) P187S Polymorphism and Prostate Cancer Risk in Caucasians

NAD(P)H:quinone oxidoreductase 1 (NQO1) catalyses the reduction of quinoid compounds to hydroquinones, preventing the generation of free radicals and reactive oxygen. A “C” to “T” transversion at position 609 of NQO1, leading to a nonsynonymous amino acid change (Pro187Ser, P187S), results in an altered enzyme activity. No NQO1 protein activity was detected in NQO1 ⁶⁰⁹TT genotype, and low to intermediate activity was detected in NQO1 ⁶⁰⁹CT genotype compared with ⁶⁰⁹CC genotype. Thus, this polymorphism may result in altered cancer predisposition. For prostate cancer, only sparse data are available. We therefore analyzed the distribution of the NQO1 P187S SNP (single nucleotide polymorphism) in prostate cancer patients and a healthy control group. Allelic variants were determined using RFLP analysis. Overall, 232 patients without any malignancy and 119 consecutive prostate cancer patients were investigated. The genotype distribution in our cohorts followed the Hardy–Weinberg equilibrium in cases and controls. The distribution of the NQO1 codon 187 SNP did not differ significantly between prostate cancer patients and the control group (p = 0.242). There was also no association between the allelic variants and stage or Gleason score of the tumors. The NQO1 P187S SNP was not significantly associated with an increased prostate cancer risk in our cohorts. The SNP has also no influence on histopathological characteristics of the tumors. A combined analysis of all available data from published European studies also showed no significant differences in the genotype distribution between controls and prostate cancer patients. Our data suggest a minor role of the NQO1 nucleotide 609 polymorphism in prostate carcinogenesis.