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- 저자 : Xiaoqing Si (검색결과 2 건)
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Xiaoqing Hu,Ju Chu,Si-Liang Zhang,Ying-ping Zhuang,Xin Wu,Huaxin Chen,Zhongyuan Lv,Zhongyi Yuan 한국생물공학회 2014 Biotechnology and Bioprocess Engineering Vol.19 No.5
Pichia pastoris is a successful system forexpressing heterologous proteins and its fermentation pH isalways maintained below 7.0. However, particular proteinsare unstable under acidic conditions, such as methionineadenosyltransferase (MAT), and thus fermentation underacidic pH conditions is unsuitable because protein activityis lost owing to denaturation. Here, a strategy employingalkaline pH in the late fermentation period was developedto improve MAT production. Initially, P. pastoris KM71was transformed with the mat gene to overexpress MAT. After 72 h of in vitro incubation at different pH values, theexpressed MAT displayed highest stability at pH 8.0;however, pH 8.0 inhibited cell growth and induced cellrupture, thus affecting protein production. To balance MATstability and Pichia cell viability, different pH controlstrategies were compared. In strategy A (reference), theinduction pH was maintained at 6.0, whereas in strategy B,it was gradually elevated to 8.0 through a 25 h transitionperiod (80 ~ 105 h). MAT activity was 0.86 U/mg (twofoldhigher than the control). However, MAT content wasreduced by 50% when compared with strategy A, becauseof proteases released upon cell lysis. To improve cellviability under alkaline conditions, glycerol was added inaddition to methanol (strategy C). When compared withstrategy B, the MAT-specific activity remained nearlyconstant, whereas the expression level increased to 1.27 g/L. The alkaline pH control strategy presented herein for MATproduction represents an excellent alternative for expressingproteins that are stable only under alkaline conditions.
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Yifei Cai,Bin Qin,Chun Li,Xiaoqing Si,Jian Cao,Xiaohang Zheng,LIANG QIAO,Junlei Qi 한국공업화학회 2023 Journal of Industrial and Engineering Chemistry Vol.120 No.-
Lithium (Li) metal is a promising material for high-energy–density batteries, but it is still plagued byobvious capacity degradation and low average Coulombic efficiency resulting from dendrite Li propagation. One main reason is the electro-mechanic coupled failure of plated Li on the current collector, whichcontributes to non-dense Li deposition on the anode. Transition metal oxides (TMOs) with a conversiontypemechanism have been used directly as the anode materials for lithium ion batteries, which demonstratedbetter electro-mechanical stability than metal Li. Herein, a successive ’’conversion-deposition’’mechanism is ingeniously developed to restrain the generation of dendritic Li. Specifically, a microcrystallineCu2O modified current collector was prepared, in which Li+ are sequentially inserted intoCu2O and deposited in the form of Li metal at successive low potential. A Li-Cu half-cell based on thehybrid mechanism sustains a high Coulombic efficiency of over 99.3 % in up to 800 cycles. This work ingeniouslyinhibits the generation of dendrite Li by incorporating conversion-type materials withdeposition-dissolution type metal Li, which contributes to a novel concept for the design of functionalcurrent collectors for composite Li anodes.
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