Yingxin Zhang

Chinese Academy of Sciences, Peping, Beijing, China

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Publications (5)5.95 Total impact

  • Hao SONG, Yingxin ZHANG, Weibao KONG, Chungu XIA
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    ABSTRACT: The activities of the key enzymes involved in the intracellular poly-3-hydroxybutyrate (PHB) synthesis of Methylosinus trichosporium IMV3011 were studied under various cultivation conditions. The enzymes were methane monooxygenase (MMO), β-ketothiolase, acetoacetyl-CoA reductase, PHB synthetase, and PHB depolymerase. Each enzyme had a unique catalytic mechanism. MMO activity decreased continuously with PHB production, but PHB at a high concentration was beneficial for maintaining MMO activity because more NADH was released by PHB depolymerization. The important reaction for entering the PHB cycle was catalyzed by β-ketothiolase. The monomer of β-hydroxybutyrate was synthesized by the catalysis of β-ketothiolase and acetoacetyl-CoA reductase. PHB synthetase played an important role in the PHB synthesis routes. The activity of PHB synthetase increased with PHB production. The changes of enzyme activities involved in PHB synthetase and PHB depolymerase occurred together, which indicated that the polymerization and depolymerization of intracellular PHB occurred simultaneously. The molecular weight of PHB was determined mainly by the combined actions of PHB synthetase and PHB depolymerase. Some important intermediates in the tricarboxylic acid cycle were helpful for PHB production because they increased related enzyme activities in the PHB cycle.摘要研究了甲烷单加氧酶 (MMO)、β-酮硫解酶、乙酰乙酰 CoA 还原酶、聚 β-羟基丁酸酯 (PHB) 合成酶及 PHB 降解酶在甲烷氧化细菌胞内 PHB 合成途径中的催化作用. 结果表明, MMO 的活性随着胞内 PHB 的积累而持续下降, 而胞内高含量的 PHB 有助于减缓 MMO 活性的降低. β-酮硫解酶控制着反应体系进入 PHB 循环的入口, 在它和乙酰乙酰 CoA 还原酶的共同作用下, 生成聚合单体 β-羟基丁酰, 二者活性在对数生长期达到峰值. PHB 合成酶可将胞内的短链片段聚合, 形成具有稳定高分子量的长链聚酯; 当 PHB 合成酶活性最高时, 胞内 PHB 浓度也随之达到峰值. 同时, PHB 降解酶活性随着 PHB 合成酶活性的增加而增加, 表明在 PHB 循环中, PHB 的合成和降解实际上是同时发生的. PHB 合成酶的活性基本决定了 PHB 的分子量, 但最终取决于 PHB 合成酶和 PHB 降解酶的共同作用.
    Chinese Journal of Catalysis 11/2012; 33(s 11–12):1754–1761. · 1.30 Impact Factor
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    ABSTRACT: Methanotrophs have promising applications in the epoxidation of some alkenes and some chlorinated hydrocarbons and in the production of a biopolymer, poly-beta-hydroxybutyrate (poly-3-hydroxybutyrate; PHB). In contrast with methane monooxygenase (MMO) activity and ability of PHB synthesis of four kinds of methanotrophic bacteria Methylosinus trichosporium OB3b, M. trichosporium IMV3011, Methylococcus capsulatus HD6T, Methylomonas sp. GYJ3, and the mixture of the four kinds of strains, M. trichosporium OB3b is the highest of the four in the activity of propene epoxidation (10.72 nmol/min mg dry weight of cell [dwc]), the activity of naphthalene oxidation (22.7 mmol/mg dwc), and ability in synthesis of PHB(11% PHB content in per gram dry weight of cell in 84 h). It could be feasible to improve the MMO activity by mixing four kinds of methanotrophs. The MMO activity dramatically decreased when the cellular PHB accumulated in the second stage. The reason for this may be the dilution of the MMO system in the cells with increasing PHB contents. It has been found that the PHB contents at the level of 1-5% are beneficial to the cells for maintenance of MMO epoxidation activity when enough PHB have been accumulated. Moreover, it was also found that high particulate methane monooxygenase activity may contribute to the synthesis of PHB in the cell, which could be used to improve the yield of PHB in methanotrophs.
    Applied biochemistry and biotechnology 01/2009; 157(3):431-41. · 1.94 Impact Factor
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    ABSTRACT: Poly-3-hydroxybutyrate (PHB) can be produced by various species of bacteria. Among the possible carbon sources, both methane and methanol could be a suitable substrate for the production of PHB. Methane is cheap and plentiful not only as natural gas, but also as biogas. Methanol can also maintain methanotrophic activity in some conditions. The methanotrophic strain Methylosinus trichosporium IMV3011 can accumulate PHB with methane and methanol in a brief nonsterile process. Liquid methanol (0.1%) was added to improve the oxidization of methane. The studies were carried out using shake flasks. Cultivation was performed in two stages: a continuous growth phase and a PHB accumulation phase under the conditions short of essential nutrients (ammonium, nitrate, phosphorus, copper, iron (III), magnesium or ethylenediamine tetraacetate (EDTA)) in batch culture. It was found that the most suitable growth time for the cell is 144 h. Then an optimized culture condition for second stage was determined, in which the PHB concentration could be much increased to 0.6 g/L. In order to increase PHB content, citric acid was added as an inhibitor of tricarboxylic acid cycle (TCA). It was found that citric acid is favorable for the PHB accumulation, and the PHB yield was increased to 40% (w/w) from the initial yield of 12% (w/w) after nutrient deficiency cultivation. The PHB produced is of very high quality with molecular weight up to 1.5×106Da.
    Journal of Natural Gas Chemistry 01/2008; 17(1):103-109. · 1.41 Impact Factor
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    ABSTRACT: The polymerization of methyl 3-hydroxypropionate as monomer catalyzed by lipase was selected as a model system in this study. The monomer with the purity around 95% could be polymerized to polyhydroxyalkanoates in the catalysis of Novozym 435. Decreasing the reaction pressure would result in the increase of product yield and high molecular weight. By choosing appropriate organic solvents, surfactants and reaction pressure, the molecular weight of polyhydroxy propionate polyester could be controlled from 1800 to 13000 (Mw value). The reusing ability of enzymatic catalyst was comparatively good. The relative activity could be maintained above 95% after 6 repeated batches reaction.摘要以 3-羟基丙酸甲酯为聚合单体, 建立了以固定化脂肪酶 Novozym 435 为催化剂的酶催化缩聚反应体系, 合成可完全降解的高分子聚酯聚羟基丙酸酯, 考察了反应条件和介质对反应性能的影响, 结果表明, 纯度大于 95% 的单体即可在温和条件下合成聚羟基羧酸酯; 降低反应压力可有效提升产物产率和分子量. 通过选择合适的有机溶剂介质和表面活性剂, 可使产物分子量提升至 13000 (Mw) 以上. 脂肪酶催化剂重复利用能力优异, 经 6 批次反应后, 其相对活性保持在 95% 以上.
    Chinese Journal of Catalysis 33(s 2–3):432–438. · 1.30 Impact Factor
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