4-Hydroxyphenylpyruvic acid(4-HPPA), a kind of α-keto acid, is an intermediate in the metabolism of tyrosine and has a wide range of application in food, pharmaceutical and chemical industry. Using amino acids as raw...4-Hydroxyphenylpyruvic acid(4-HPPA), a kind of α-keto acid, is an intermediate in the metabolism of tyrosine and has a wide range of application in food, pharmaceutical and chemical industry. Using amino acids as raw material to produce the corresponding α-keto acid is thought to be both economic and efficient. Among the enzymes that convert amino acid to α-keto acid, membrane bound L-amino acid deaminase(mL-AAD), which is anchored to the outer side of the cytomembrane, becomes an ideal enzyme to prepare α-keto acid since there is no cofactors needed and H_2 O_2 production during the reaction. In this study, the mL-AAD from Proteus vulgaris was used to prepare whole-cell catalysts to produce 4-HPPA from L-tyrosine. The secretory efficiency of mL-AAD conducted by its own twin-arginine signal peptide(twin-arginine translocation pathway, Tat) and integrated pelB(the general secretory pathway, Sec)-Tat signal peptide was determined and compared firstly, using two pET systems(pET28 a and pET20 b). It was found that the Tat pathway(pET28 a-mlaad) resulted in higher cell-associated mL-AAD activity and cell biomass, and was more beneficial to prepare biocatalyst. In addition, expression hosts B121(DE3) and 0.05 mmol ·L^(-1) IPTG were found to be suitable for mL-AAD expression. The reaction conditions for mL-AAD were optimized and 72.72 mmol·L^(-1) 4-HPPA was obtained from 100 mmol·L^(-1) tyrosine in 10 h under the optimized conditions. This bioprocess, which is more eco-friendly and economical than the traditional chemical synthesis ways, has great potential for industrial application.展开更多
This paper investigates the factors affecting the conservatism of accounting reports at the market-level and firm-level. At the market-level, law and institutional factors explain conservatism, while at the firm-level...This paper investigates the factors affecting the conservatism of accounting reports at the market-level and firm-level. At the market-level, law and institutional factors explain conservatism, while at the firm-level contracting is the driver. We predict and observe that while both levels jointly affect conservatism, it is firm-level factors that play a dominant role. The conclusion suggests that it is more effective to improve the quality of accounting reports by motivating the firm's own demand rather than through listing in a developed capital market.展开更多
基金Supported by the National Natural Science Foundation of China(31470793,31670804)China Postdoctoral Science Foundation(2016M592003)+1 种基金the Natural Science Foundation of Zhejiang Province(LZ13B060002)the General Scientific Research Project of Zhejiang Provincial Education Department(Y201432760)
文摘4-Hydroxyphenylpyruvic acid(4-HPPA), a kind of α-keto acid, is an intermediate in the metabolism of tyrosine and has a wide range of application in food, pharmaceutical and chemical industry. Using amino acids as raw material to produce the corresponding α-keto acid is thought to be both economic and efficient. Among the enzymes that convert amino acid to α-keto acid, membrane bound L-amino acid deaminase(mL-AAD), which is anchored to the outer side of the cytomembrane, becomes an ideal enzyme to prepare α-keto acid since there is no cofactors needed and H_2 O_2 production during the reaction. In this study, the mL-AAD from Proteus vulgaris was used to prepare whole-cell catalysts to produce 4-HPPA from L-tyrosine. The secretory efficiency of mL-AAD conducted by its own twin-arginine signal peptide(twin-arginine translocation pathway, Tat) and integrated pelB(the general secretory pathway, Sec)-Tat signal peptide was determined and compared firstly, using two pET systems(pET28 a and pET20 b). It was found that the Tat pathway(pET28 a-mlaad) resulted in higher cell-associated mL-AAD activity and cell biomass, and was more beneficial to prepare biocatalyst. In addition, expression hosts B121(DE3) and 0.05 mmol ·L^(-1) IPTG were found to be suitable for mL-AAD expression. The reaction conditions for mL-AAD were optimized and 72.72 mmol·L^(-1) 4-HPPA was obtained from 100 mmol·L^(-1) tyrosine in 10 h under the optimized conditions. This bioprocess, which is more eco-friendly and economical than the traditional chemical synthesis ways, has great potential for industrial application.
基金supported by Program for New Century Excellent Talents in University
文摘This paper investigates the factors affecting the conservatism of accounting reports at the market-level and firm-level. At the market-level, law and institutional factors explain conservatism, while at the firm-level contracting is the driver. We predict and observe that while both levels jointly affect conservatism, it is firm-level factors that play a dominant role. The conclusion suggests that it is more effective to improve the quality of accounting reports by motivating the firm's own demand rather than through listing in a developed capital market.
