Preparation and properties of RNase T2 immobilized on concanavalin A-sepharose

Partially purified RNase T2 (EC 2.7.7.17) from Aspergillus oryzae was bound through its carbohydrate moiety to Concanavalin A-Sepharose. The retention of activity was high, ranging from 70% at low enzyme load to approximately 9% at high enzyme load. Though there was no change in the pH and temperature optima, the pH stability and the Km decreased after immobilization. Compared to the soluble enzyme, the immobilized RNase T2 showed enhanced temperature stability and more resistance to metal ions. Both soluble and immobilized enzymes were stable to 8 M urea. On repeated use, the bound enzyme retained more than 60% of its initial activity after six cycles.     

Efficient cellulose solubilization by a combined cellulosome-β-glucosidase system

The cellulosome, the multienzyme complex of the cellulase system ofClostridium thermocellum, that mediates the solubilization of insoluble cellulose, is strongly inhibited by the major end product, cellobiose. By combining a purified β-glucosidase fromAspergillus niger with the cellulosome, accumulated cellobiose was hydrolyzed thereby resulting in a dramatic enhancement (up to 10-fold) of cellulose degradation. The observed enhancement was expressed both in the rate and degree of solubilization of microcrystalline cellulose, compared with that observed for the unsupplemented cellulosome. Near-complete conversion of cellulose to glucose could be obtained from dense substrate suspensions (up to at least 200 g/L).     

Synthesis of Optically Active Hydroxyesters Using Biocatalysts

Optically active hydroxyesters were prepared using the fungusAspergillus nigerand the yeastSacharomyces cerevisiae.Substrate is converted highly specifically into optically active isomers with 95% purity. The R-hydroxyester was isolated by asymmetric reduction. (R,R)-Tartaric acid of 60% optical purity was used as an inductor     

Chitosan Obtained from Cell Wall of Aspergillus Niger Mycelium

Chitin from cell walls of Aspergillus Niger mycelium was prepared. A new method for the preparation of high deacetylation degree chitosan was studied in a dilute sodium hydroxide solution at a high pressure. The experimental results indicate that the deacetylation degree of the chitosan can reach 80% under the condition of a 5.00 mol/L sodium hydroxide solution at 0. 1 MPa of pressure for 1 h. This method shows the advantages of the applications in the industry production and environment protection.     

Isochromanes from Aspergillus fumigatus,an endophytic fungus from Cordyceps sinensis

Four previously undescribed isochromanes were isolated from the fermentation broth of an endophytic fungus Aspergillus fumigatus, which was obtained from the fruiting body of Cordyceps sinensis. Their structures were elucidated through extensive spectroscopic analyses. One racemic isochromane was further purified by chiral HPLC to yield a pair of enantiomers and their absolute configurations were determined by quantum chemical ECD calculations. These isolated compounds were evaluated for cytotoxicity against two cell lines (MV4-11 and MDA-ME-231) and the result showed that compounds 1a and 2 exhibited moderate growth inhibition against MV4-11 cell line.     

Sphingofungins G and H: new five-membered lactones from Aspergillus penicilliodes Speg.

Two new sphingofungins G (1) and H (2) with a five-membered lactone ring were identified from the solid-state fermentation of Aspergillus penicilliodes Speg., a dominant microorganism isolated previously from the post-fermentation of ripe Pu-er tea, together with six known metabolites. Their structures were elucidated by extensive spectroscopic methods. All of them were isolated from the mycelia culture of A. penicilliodes for the first time. The known compound, trypacidin, exhibited potent cytotoxities against five human cancer cell lines, e.g. myeloid leukemia HL-60, lung cancer A-549, hepatocellular carcinoma SMMC7721, breast cancer MCF-7, and colon cancer SW480, with IC₅₀ values of 0.55, 11.45, 10.95, 3.58, and 3.49 μM, resp., while cisplatin as the positive control, with IC₅₀ values of 8.63, 24.15, 21.99, 27.29, and 23.61 μM, resp.     

棘孢曲霉β-葡萄糖苷酶Ⅰ在毕赤酵母中的表达及烷基糖苷的催化合成

将来自棘孢曲霉(Aspergillus aculeatus NO. F-50)的β-葡萄糖苷酶Ⅰ在毕赤酵母中分泌表达. 初步研究表明, 目的蛋白得到较好表达, 以对硝基酚-β-D-葡萄糖苷(4-Nitrophenyl-β-D-glucopyranoside, pNPG)为底物, 重组β-葡萄糖苷酶Ⅰ酶促反应的最适温度为65 ℃, 最适pH为5.0, 50 ℃下反应发酵上清液中的酶活力可达33.8 U/mL, 蛋白表达量最高可达0.388 mg/mL. 该重组酶可通过逆水解或转糖苷反应催化合成烷基糖苷. 在有机-水双相反应体系中, 初步优化了pH 值、 含水量、 葡萄糖浓度及酶量等条件. 结果表明, 在优化的反应条件下, 丁基、 己基、 辛基和癸基葡萄糖苷最大产率分别为51.4%, 28.8%, 6.9%和3.0%.     

Protection of aspergillus niger cellulases by urea during growth on glucose or glycerol supplemented media

The cellulase enzymes ofAspergillus niger were found to undergo catabolite repression in the presence of glucose and glycerol accompanied by sudden drop in pH of the fermentation medium below 2.0. This sudden drop in pH caused inactivation of cellulolytic enzymes produced byAspergillus niger. The supplementation of nitrogen sources, especially urea, protectsA. niger cellulases from inactivation caused by a sudden drop in pH, since urea helped to maintain the pH of the fermentation medium between 3.5 and 4.5. The role of urea in the protection of cellulase was more prominent when it was used in combination with glycerol (5%).