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91.
92.
Jian-Yi Sun Ming-Qi Liu Xiao-Yan Weng Li-Chun Qian Sai-Hong Gu 《Food chemistry》2007,104(3):1055-1064
The mature peptide of Thermomonospora fusca xylanase A (TfxA) was successfully expressed in Pichia pastoris under the control of AOX1 promoter. The activity of recombinant T. fusca xylanase A (reTfxA) in culture supernatant was 117.3 ± 2.4 U/mg, which is 3 times higher than that of the native TfxA. The optimal temperature and pH for reTfxA were 60 °C and 6.0, respectively. When treated at 70 °C and pH 6.0 for 2 min, the residual activity of the reTfxA was 70%. The reTfxA was very stable over a wide pH range (5.0–9.0). After incubation over pH 5.0–9.0 at 25 °C for 1 h, all the residual activity of reTfxA was over 80%. The Km and kcat values for reTfxA were 2.45 mg/ml and 139 s−1, respectively. HPLC analysis revealed that xylobiose (X2) was the main hydrolysis product released from birchwood xylan and wheat bran insoluble xylan by reTfxA. Hydrolysis results of xylooligosaccharides showed that reTfxA was an endo-acting xylanase and xylobiose, xylotriose (X3), xylotetraose (X4), xylopentaose (X5), and xylohexaose (X6) could be hydrolysed. This is the first report on the expression of reTfxA in yeast and on the determining and quantifying of the hydrolysis products released from xylans and xylooligosaccharides by reTfxA. 相似文献
93.
常温酸水解法从稻壳中提取木糖的研究 总被引:4,自引:0,他引:4
以较高浓度的硫酸为浸取剂,在常温常压下浸泡稻壳12 ̄15h,浸出液经中和、蒸发、脱色、离子交换、浓缩、结晶制取木糖。并采用正交实验法研究了常温常压水解条件对木糖得率的影响,最后确定了最佳的水解工艺条件,和以前的常用工艺比较,不但节约了大量的能耗,而且使木糖得率也大幅度的提高。 相似文献
94.
微区框栽、田间试验和示范对比田均证实增产菌明显增加甜菜块根产量,并有提高含糖率的趋势。拌种处理对苗期立桔病、叶喷处理对中后期褐斑病有一定的抑制作用。增产菌处理提高叶片硝酸还原酶活性,增强植株氮、磷、钾的吸收能力、明显增加根中细胞分裂素(DHZRs)、赤霉素(GA_(1·3·4·7))、生长素(IAA)的含量,降低根中脱落酸(ABA)含量,导致根中DHZRs+GA_(1·3·4·7)+IAA与ABA比率增高。上述结果是甜菜施用增产菌丰产增糖的主要机理。 相似文献
95.
Agnieszka?NowakEmail author Danuta?Kusewicz Halina?Kalinowska Marianna?Turkiewicz Piotr?Patelski 《European Food Research and Technology》2004,219(1):84-89
Correlation between H2S productivity (p) and sulfite reductase activity (A) was estimated for seven wine-producing yeasts. It was described by a linear function
p=f(A), the slope of which depended on the yeast strain. The most intensive H2S synthesis by all the examined yeasts was observed within the early logarithmic growth phase, either in nitrogen abundance and SO2 presence, or in nitrogen deficient and SO2-free medium. Sulfite reductase from all the strains was optimally active at pH close to 7.4. The enzyme from cryophilic yeasts displayed maximum activity at approximately 16 °C, and from mesophiles at 22–26 °C. The preparations showed different affinities toward sulfite (Km of 16.7–67.5 M). Values of activation energy in sulfite reduction depended on the yeast, and ranged from 14.07 to 67.04 kJ mol–1. 相似文献
96.
Simn J Tllez‐Luis Jos A Ramírez Manuel Vzquez 《Journal of the science of food and agriculture》2002,82(5):505-512
Sorghum straw is a renewable, cheap and widespread resource. The acid hydrolysis of sorghum straw to obtain xylose solutions could be a good alternative for this abundant resource. The H2SO4 hydrolysis of sorghum straw at two different temperatures (80 and 100 °C) and three H2SO4 concentrations (2, 4 and 6%) using a solid/liquid ratio of 1:10 (w/w) was studied. Kinetic parameters of mathematical models for predicting the concentrations of xylose, glucose, acetic acid and furfural were determined. The activation energy of the release reaction was 183.3 kJ mol?1 for xylose and 185.8 kJ mol?1 for glucose. The optimal conditions found were 6% H2SO4 at 100 °C for 60 min, which allow one to obtain a solution with 18.27 g xylose l?1, 6.78 g glucose l?1, 0.7 g furfural l?1 and 1.35 g acetic acid l?1. It is concluded that this process has potential for utilisation of this renewable lignocellulosic resource. © 2002 Society of Chemical Industry 相似文献
97.
98.
The effect of N fertilizers on nodulation, nitrogenase, nitrate reductase activities and growth of two cultivars of soybean, Clark and Crauford was evaluated in a field experiment. KNO3 or NH4Cl were applied 27 days after planting at 0,16, 32, 64 and 128 kg N/ha. Nodulation and growth of both cultivars significantly increased when N was applied at low levels whereas specific N2-ase activity (SNA) slightly and insignificantly increased. Cv Crauford showed a greater positive response than cv. Clark. Higher rates of KNO3 and NH4Cl (128 kg N/ha) significantly depressed nodulation and SNA but slightly decreased the plant dry matter. Cv. Crauford was more tolerant to N fertilizers than cv. Clark. The decline in SNA was ascribed to increased nitrate reductase activity (NRA) and higher accumulation of nitrites in nodule cytosol. NRA and nitrate contents in nodules of cv. Clark were greater than that in cv. Crauford. Results showed that NH4
+ is the preferred N source with occasional increases in nodule number and weight. This study provides an evidence for the nodulation and growth variability of soybean cultivars fertilized with different levels of N. The results also suggest that diminishing NRA could contribute to increased N2 fixation and the interaction between NO3
– assimilation and N2 fixation is strongly dependent on the plant cultivar. 相似文献
99.
Ulrike Vogel Dr. Matthieu Da Costa Carlos Alvarez Quispe Robin Stragier Dr. Henk-Jan Joosten Dr. Koen Beerens Prof. Dr. Tom Desmet 《Chembiochem : a European journal of chemical biology》2023,24(23):e202300549
A promiscuous CDP-tyvelose 2-epimerase (TyvE) from Thermodesulfatator atlanticus (TaTyvE) belonging to the nucleotide sugar active short-chain dehydrogenase/reductase superfamily (NS-SDRs) was recently discovered. TaTyvE performs the slow conversion of NDP-glucose (NDP-Glc) to NDP-mannose (NDP-Man). Here, we present the sequence fingerprints that are indicative of the conversion of UDP-Glc to UDP-Man in TyvE-like enzymes based on the heptagonal box motifs. Our data-mining approach led to the identification of 11 additional TyvE-like enzymes for the conversion of UDP-Glc to UDP-Man. We characterized the top two wild-type candidates, which show a 15- and 20-fold improved catalytic efficiency, respectively, on UDP-Glc compared to TaTyvE. In addition, we present a quadruple variant of one of the identified enzymes with a 70-fold improved catalytic efficiency on UDP-Glc compared to TaTyvE. These findings could help the design of new nucleotide production pathways starting from a cheap sugar substrate like glucose or sucrose. 相似文献
100.
Two anthocyanins (cyanidin-3-O-β-glucoside and peonidin-3-O-β-glucoside) and other phenolic (ferulic acid) were, respectively isolated from black and pigmented brown rices (Oryza sativa L. japonica) and their complete structures were determined by spectroscopic analyses (H NMR, C NMR and MALDI MASS). The HPLC profile of anthocyanins extracted from black rice showed cyanidin-3-O-β-glucoside as the first peak (85%) and peonidin 3-O-β-d-glucoside as the second (15%), while that of pigmented brown rice showed ferulic acid as the first peak (85.7%) and tocols as the second (14.3%). Several tocols were isolated and identified from the unsaponifiable fractions of both rices having some difference on their structures and amounts. The aldose reductase inhibitory activity of isolated compounds was in the following decreasing order: cyanidin-3-glucoside > quercetin > ferulic acid > peonidin-3-glucoside > tocopherol. 相似文献