Cloning and Expression of One Fibrinolytic Enzyme from Bacillus sp. zlw-2

The gene encoding fibrinolytic enzyme from Bacillus sp. zlw-2 was cloned and sequenced （accession no. EU734749）, which was 1146 bp, encoded 381 amino acids and had 99% homology with Nattokinase YF308 and NAT. The genes encoding pre-pro-fibrinolytic enzyme （including signal peptide, propeptide, and mature peptide） and fibrinolytic enzyme （including mature peptide） were cloned into pET28a vector respectively and then transformed into Escherichia coli BL21 （DE3）. The recombinant ofpre-pro-fibrinolytic enzyme showed enzyme activity of 183 U mL^-1, while no detectable enzyme activity could be found from the recombinant of the mature peptide.

Cloning,expression in Escherichia coli,and enzymatic properties of laccase from Aeromonas hydrophila WL-11

A strain WL-11 with high laccase activity was isolated from activated sludge collected from the effluent treatment plant of a textile and dyeing industry. It was identified as Aeromonas hydrophila by physiological test and 16S rDNA sequence analysis. A gene encoding of laccase from a newly isolated Aeromonas hydrophila WL-11 was cloned and characterized. Nucleotide sequence analysis showed an open reading frame of 1605 bp encoding a polypeptide comprised of 534 amino acids. The primary structure of the enzyme predicted the structural features characteristic of other laccases, including the conserved regions of four histidine-rich copper-binding sites. The predicted amino acid sequence showed a high homology （more than 60%） with bacterial laccases in the genome and protein databases and the highest degree of similarity （61% identity） was observed with the multicopper oxidase of KlebsieUa sp. 601. When expressed in Escherichia coli, the recombinant enzyme was overproduced in the cytoplasm as soluble and active form. The purified enzyme had an optimum pH of 2.6 and 8.0 for ABTS （2,2＇-azino-bis（3-ethylbenzthiazolinesulfonic acid） and DMP （2,6-dimethoxyphenol）, respectively. The kinetic study on ABTS revealed a higher affinity of this enzyme to this substrate than DMP.

Characterization and Expression Analysis of Starch Branching Enzymes in Sweet Potato

Spatial and temporal expression patterns of Sbel and Sbe2 that encode starch branching enzyme （SBE） Ⅰ and Ⅱ, respectively, in sweet potato （Ipomoea batatas L.） were analyzed. Expression of both genes in Escherichia coli indicate that both genes encoded active SBE. Analysis with real-time quantitative polymerase chain reaction technique indicates that IbSbel mRNA was expressed at very low levels in leaves but was the predominant isoform in tuberous root while the reverse case was found for lbSbe2. The expression pattern of IbSbel, closely resembles that of AGPase S, a gene coding for one of the subunits ofADP-glucose pyrophosphorylase, which is the key regulatory enzyme in the starch biosynthetic pathway. Western analysis detected at least two isoforms of SBE I in tuberous roots, those two isoforms showed adverse expression patterns with the development of the tuberous roots. Expression of the two IbSbe genes exhibited a diurnal rhythm during a 12-h cycle when fed a continuous solution of sucrose. Abscisic acid （ABA） was aother potent inducer of IbSbe expression, but bypassed the semidian oscillator.

Characterization, gene cloning and expression of new xylanase XYNB with high specific activity

Extracellular xylanase XYNB from Streptomy-ces olivaceoviridis A1 has been purified and characterized. The optimal pH value and temperature of XYNB for its ac-tivity are 5.2 and 60℃, respectively. The specific activity of XYNB is as high as 2869.78 U/mg. Metal cations, EDTA and SDS have no effects on enzyme activity of XYNB. The gene xynB coding mature protein of XYNB has been cloned by PCR. The forward oligonucleotide primer used in the PCR reaction was synthesized based on the N-terminal amino acid sequence of XYNB mature protein, and the reverse oligonu-cleotide primers are random oligonucleotide. The cloned gene xynB is 576 bp long and its G+C content is 64.3%. The xynB encodes 191 amino acid residues, and the putative mo-lecular weight of XYNB is 20.839 kD. The xynB has been expressed in E. coli, and the expressed xylanase has normal bioactivity.

Cloning and Characterization of a Galactomannan-degrading Enzyme Gene in Pichia pastoris

[ Objective ] This study aimed to obtain the recombinant Pichia yeast strain which can efficiently degrade guar gum. The properties of the recombinant enzyme were studied preliminarily. [ Method ] A positive clone that could hydrolyze guar gum was obtained through the construction and functional screening of a soil genome library. Sequence analysis indicated that the 1485-bp clone encodes a 494-amino acid protein with a relative molecular mass of 53 949 kD, containing a cellulose-binding domain. The recombinant plasmid pHBM731 was generated by inserting the optimized target gene into a Pichia pastoris expression vector pHBMg05 that was transformed into three Pichia pastoris strains, GS115, KM71 and SMD1168. The biochemical properties of the enzyme were assessed. [ Result] The cloned galactonumnan （GM）-degrading enzyme was expressed and secreted by Pichia pastoris GSll5. High cell density fermentation was induced in recombi- nant Pichia pastoris at 25 and 28 ~C ; a higher enzyme activity was observed at an induction temperature of 28 ~C. The optimal temperature for the recombinant en- zyme is 60 ~C, and the optimal pH is 6.6. The enzyme activity was 38.61 U under optimal conditions. Over 50% of the enzyme activity was maintained under the optimal conditions after 9 h. Under the optimal conditions, the effect of metal ions on enzyme activity was analyzed. Ca2 ＋ , Fe2 ＋ and Li ~ slightly enhanced enzyme activity, while Mn2＋ and Co2＋ had little effect. Enzyme activity was modestly suppressed by Mg2~ , K~ and Na＋ , but considerably suppressed by Ag2~ and Zn2~ , with Cu2 ＋ showing the strongest inhibitory effects. [ Conclusion] A novel GM-degrading enzyme expressed by soil yeast was cloned, which can potentially be used in industrial applications to obtain eommereially useful guar gum-degradation products.

Cloning, expression and characterization of a feruloyl esterase C from Penicillium chrysogenum

Objective:To clone feruloyl esterase gene C from Penicillium chrysogenum and characterize the general properties of the enzyme.Methods:The feruloyl esterase C gene was amplified by PCR based on the Penicillium chrysogenum feruloyl esterase C gene sequence and cloned into the expression vector p PIC9K,resulting the recombinant plasmid p PIC9K-Pcfae C.The recombiant plasmid was linerized and transformed into P.pastoris by electroporation.The transformants was screened based on the transparent zone technology.The screened transformants was then induced by methanol.the enzymatic properties of the protein were then measured.Results:SDS-PAGE analysis showed that the molecular mass of the enzyme was about 30 k D.The length of the gene was 762 bp.It comprised one open reading framwork(ORF)and annotated to encode 249 amino acid.The optimal temperature and p H was found to be 40℃and 6,respectively.Moreover,the recombinant enzyme was stable at 40-50℃and p H 5-7.Conclusion:The enzyme successfully expressed in P.pastoris could laid theoretical foundation in food,fodder and paper making industry.

吡虫啉胁迫对红光熊蜂抗氧化酶系与解毒酶系的影响

为探究亚致死剂量吡虫啉胁迫对红光熊蜂工蜂的存活率、解毒酶活力与解毒基因表达量的影响,采用cDNA末端快速扩增技术(RACE)克隆红光熊蜂工蜂(21日龄)解毒基因,检测其表达量变化与抗氧化酶的活性,并通过饲喂外源褪黑素以提高熊蜂的抗药性.结果表明:随着胁迫时间的延长,吡虫啉处理组(IMI组)存活率显著下降,但始终低于吡虫啉+褪黑素处理组(IMI+MT组);IMI组4种抗氧化酶的活性均随吡虫啉胁迫时间的延长呈先上升后下降的趋势,始终低于IMI+MT组;IMI组8种解毒基因的表达量除AChE,DDTase和GLD基因外,其余表达量均随吡虫啉胁迫时间的延长呈先激活后抑制的状态,且明显高于对照组(CK组)而低于IMI+MT组;IMI组DDTase基因的表达量与CK组差异不明显,但始终低于IMI+MT组,说明吡虫啉对DDTase的作用不明显,而褪黑素诱导DDTase表达效果较显著(P<0.05);IMI组AChE和GLD基因的表达量均低于CK组,随吡虫啉胁迫时间的延长而呈下降趋势,但IMI+MT组二者的表达量始终高于IMI组.短期亚致死剂量吡虫啉胁迫对红光熊蜂影响不显著,长期胁迫则影响其存活率,红光熊蜂对吡虫啉的代谢解毒是一个多酶系、多基因协同参与的理化过程,褪黑素可提高红光熊蜂的抗药性.

西方蜜蜂AmAGO1蛋白的分子特性、时空表达谱及抗体制备

【目的】Argonaute(AGO)家族是一类在进化上高度保守的蛋白家族,其在真核生物中主要参与形成RNA诱导沉默复合体(RNA-induced silencing complex,RISC),进而通过沉默基因表达参与诸多生物学过程。蜜蜂AGO蛋白的相关研究迄今仍然缺失。本研究拟通过预测西方蜜蜂Apis mellifera的AGO1(AmAGO1)理化性质和分子特性,解析AmAGO1在西方蜜蜂中的时空表达谱,并制备AmAGO1的多克隆抗体,为深入开展AmAGO1的功能与机制研究提供参考和基础。【方法】PCR扩增西方蜜蜂AmAGO1的编码序列(coding sequence,CDS);通过生物信息学预测AmAGO1蛋白的理化性质和分子特性;利用RT-qPCR检测AmAGO1在西方蜜蜂工蜂卵、3日龄幼虫、7日龄预蛹、8日龄预蛹、12日龄蛹以及1,2,6,12,15和18日龄成虫以及工蜂成虫触角、咽下腺、脑、表皮、中肠、脂肪体和毒腺中的表达量;构建原核表达质粒后诱导表达AmAGO1融合蛋白,并鉴定其表达形式;制备AmAGO1多克隆抗体,利用ELISA,Western blot和免疫沉淀(immunoprecipitation,IP)分别检测抗体效价、灵敏度和特异性。【结果】成功克隆到西方蜜蜂AmAGO1的CDS;AmAGO1含928个氨基酸,分子式为C4624H7332N1316O1325S51,分子量约为104.2 kD,等电点为9.31,平均亲水系数为-0.2965,含86个磷酸化位点及典型的PAZ结构域和PIWI结构域,但不存在典型的信号肽;AGO1在智人Homo sapiens、斑马鱼Danio rerio、黑腹果蝇Drosophila melanogaster、家蚕Bombyx mori、西方蜜蜂、东方蜜蜂A.cerana和欧洲熊蜂Bombus terrestris中具有较高的氨基酸序列一致性;西方蜜蜂和东方蜜蜂的AGO1聚为一支,同源性最高。AmAGO1在西方蜜蜂工蜂卵、幼虫、预蛹、蛹和成虫中均有表达但表达量存在差异,3日龄幼虫和7日龄预蛹中AmAGO1的表达量显著低于卵中的表达量,而8日龄预蛹和12日龄蛹中AmAGO1的表达量显著高于卵中的表达量;AmAGO1在1,2,6,12,15和18日龄工蜂体内均有表达但表达量也存在差异,其中1日龄成虫体内AmAGO1的表达量显著高于其他日龄成虫体内的表达量;AmAGO1在工蜂成虫触角、毒腺、脑、中肠、咽下腺、脂肪体和表皮中均有表达但表达量存在差异,触角中AmAGO1的表达量与咽下腺中的相差无几,但二者均显著高于毒腺、脑、中肠、脂肪体和表皮中AmAGO1的表达量;AmAGO1融合蛋白的表达形式为包涵体;制备的AmAGO1多克隆抗体具有较高的效价、灵敏度和特异性。【结论】AmAGO1可能是亲水性胞内蛋白,含有典型的PAZ结构域和PIWI结构域;AmAGO1在西方蜜蜂工蜂不同组织和不同发育阶段发挥潜在的重要功能;成功制备出高效价、高灵敏度和强特异性的AGO1多克隆抗体。

南极假丝酵母(Candida antarctica)脂肪酶A在毕赤酵母中的表达、纯化及性质

将编码南极假丝酵母脂肪酶A的基因进行克隆,与pPIC9K连接构建成重组载体,并将其电转化入毕赤酵母GS115中。通过MD和MM平板及PCR扩增,筛选和鉴定重组子。重组细胞经过120 h培养后,发酵液上清酶活达到13 U/mL。聚丙烯酰胺凝胶电泳显示,重组脂肪酶分子量约为50 kD,比原始脂肪酶略大。粗酶液经中空纤维素膜超滤浓缩、硫酸铵分级沉淀和离子柱交换层析后,得到在SDS-PAGE上显示为单一条带的重组脂肪酶。该酶最适反应温度为75℃,在70℃保持30 min后,仍具90%以上的活性,最适反应pH值为7.0,在pH6.0～8.0的范围内,具有一定的稳定性。

薰衣草醇酰基转移酶基因(AAT)的克隆和表达分析

醇酰基转移酶(AAT)可以催化乙酰辅酶A与萜烯醇类物质的结合,生成各类乙酸酯类化合物。为探明薰衣草AAT基因在酯类化合物合成中的调控作用,本研究以薰衣草品系杂花叶片为供试材料,利用反转录PCR技术克隆薰衣草AAT基因的cDNA序列,该cDNA序列长度为1344 bp,其编码蛋白质由447个氨基酸组成,是非跨膜亲水性蛋白质,属于PLN02481超级家族;薰衣草AAT与黄色猴面花EgAAT亲缘关系最近,相似度为60.87%。AAT基因在苞叶中的表达量最低,在花瓣中的表达量最高;在花冠不同发育时期,该基因在盛开期表达量到达峰值。构建原核表达载体pET-28a-AAT,筛选了重组蛋白在大肠杆菌Transetta(DE3)中的最适诱导表达条件,诱导后获得的重组蛋白质相对分子质量为5.026×10^(4),重组蛋白以包涵体形式存在,具有将芳樟醇催化合成乙酸芳樟酯的生物活性。本研究结果为进一步验证薰衣草AAT基因在酯类化合物合成过程中的功能提供了基础。

弧菌DS32褐藻胶裂解酶基因vralg1的异源表达和酶学性质研究

对从福建省东山湾沉积物样品中筛选到的菌株Vibrio sp. DS32的褐藻胶裂解酶基因vralg1进行克隆和异源表达,并对其酶学性质进行评估。以DS32基因组为模板,克隆褐藻胶裂解酶基因vralg1,构建了pET-vralg1重组表达载体,并在大肠杆菌中实现了异源表达,对重组酶VRALG1的酶学性质、底物特异性和完全降解产物等进行了测定。结果表明:重组酶VRALG1最适温度为35℃,在5~50℃范围内相对酶活力达到80%以上,最适pH为6.5~7.5,在pH为6.0~9.0范围内保温1 h后相对酶活力在90%以上;重组酶VRALG1最大反应速率为5.919 mmol/(L·min),米氏常数为3.712 mmol/L,最适条件下比活力为5.874 U/mg;K^(+)、Cs^(+)、Na^(+)、咪唑和乙醇对酶活性影响较小,5 mmol/L或50 mg/mL浓度下相对酶活力保持90%以上,EDTA对酶的抑制作用明显,1 mmol/L浓度下可使酶完全失活;重组酶VRALG1对海藻酸钠和聚古罗糖醛酸具有较高的降解活性,TLC分析显示产物主要为单糖、二糖和三糖混合物,结合底物特异性分析,推测重组酶VRALG1是具有明显聚古罗糖醛酸偏好性的内切型双功能褐藻胶裂解酶。本研究成功克隆了弧菌DS32中褐藻胶裂解酶基因并实现了其在大肠杆菌中的异源表达,所得重组酶VRALG1具有优良的海藻酸钠降解活性和明显的聚古罗糖醛酸偏好性,可以用于制备低聚合度的褐藻寡糖。

Molecular cloning,in vitro expression and enzyme activity analysis of violaxan-thin de-epoxidase from Oryza sativa L.

The violaxanthin de-epoxidase gene was cloned from rice (Oryza sativa subsp. japonica). The full length of the cDNA is 1887 bp, encoding a 446-amino acids protein with the transit peptide of 98 amino acids. The bacterial expression vector pET-Rvde was constructed and the expression quantity of the exogenous protein increased with the induction time by 0.4 mmol/L IPTG. Its molecular weight was similar with that of the native VDE. Western blotting indicated that the expressed protein has immu-nological reaction with the VDE polyclonal antibody. The absorbance spectrum together with xanthophyll pigments quantification by HPLC demonstrated that the expressed VDE has its enzyme activity, which can de-epoxidate violaxanthin into antheraxanthin and zeaxanthin in vitro.

Specific Expression of Maize SBEIIb Promoter Mediated by Different Promoter Region in Transgenic Tobacco Plants

Starch branching enzyme （SBE） catalyzes the biosynthesis of amylopectin. We described the isolation and characterization of SBEIIb promoter and their expression patterns in transgenic tobacco. Using the genomic DNA of maize cultivar Lunuo 1 as template, the SBEIIb promoter was isolated by PCR and was cloned into pMD18-T vector. To study SEBIIb gene regulation at the cellular level, SBEIIb promoter was fused to the ^-glucuronidase （GUS） report gene. The results of the fluorometric GUS assays indicate that the sbeⅡb-GUS fusion directed a seed-specific expression. Four series of constructs were made with the promoter and the GUS reporter gene to investigate the cis-acting analysis, showing that the four different constructs all can drive expression of the GUS gene in seed plumule and cotyledon and the GUS activity was apparently decreased with the progressive loss of promoter 5＇ end.

Leifsonia菌β-葡萄糖苷酶(Lf18920)的酶学性质研究及对藏红花素转化作用的初步研究

克隆表达了一种赖氏菌(leifsonia spp. ZF2019)的一个GH3家族糖苷酶基因(Lf18920),以pET-28a-HMT为载体构建了表达质粒,在大肠杆菌BL21中诱导表达,用Ni-NTA柱纯化表达蛋白。研究了该酶的底物特异性及动力学参数,分析了温度、pH、金属离子等因素对该酶活性的影响,并采用高效液相色谱和液质联用色谱探究了该酶对藏红花素的转化作用。结果表明:该酶与4-硝基苯基-β-D-吡喃葡萄糖苷(4-nitrophenyl beta-D-glucopyranoside,pNPG)的亲和力最强,对底物pNPG的特征常数Vmax和Km分别为0.155U/mg和1.97 mmol/L。该β-糖苷酶的最适温度为40℃,最适pH为5.0;低浓度的Zn2+使酶活提高了37%左右,SDS和吡啶可以使酶完全失活,可耐受1%的尿素(仍能保持77%的相对酶活)。该酶能部分水解藏红花素,但不能将其彻底水解成藏红花酸。研究结果表明,该酶可用于以藏红花素为底物的不同水解度藏红花苷的制备。

贝莱斯芽孢杆菌角蛋白酶的克隆表达、纯化及酶学性质

为了获得更好的羽毛粉降解酶,作者从贝莱斯芽孢杆菌基因组中筛选到一个角蛋白酶基因(baker1),对其克隆并在大肠杆菌BL21(DE3)中异源表达,最后对重组角蛋白酶(BaKer1)进行分离纯化、表征及应用研究。结果表明,BaKer1的最适反应pH为9.5,最适反应温度为55℃,在中温和碱性条件下具有较好的稳定性。1 mmol/L Ca^(2+)对BaKer1有显著促进作用,5 mmol/L Mn^(2+)对BaKer1有轻微抑制作用,其他金属离子对BaKer1影响不大。PMSF对BaKer1的活性具有显著抑制作用,表明BaKer1是典型的丝氨酸蛋白酶。分别以羽毛粉、偶氮酪蛋白、酪蛋白为底物测定了BaKer1的动力学参数,Km值分别为5.06、1.09、1.39 mmol/L,k_(cat)/K_(m)值分别为1058.24、2536.54、3733.79 s·mmol/L。BaKer1处理羽毛粉,能达到酸水解效果的33.51%,说明它在羽毛粉降解过程中具有潜在的应用价值。

牛瘤胃内切葡聚糖酶基因在大肠杆菌中的克隆与表达

为提高纤维素的降解效率、构建高效表达的纤维素酶基因工程菌,本研究以牛瘤胃液微生物全基因组为模板,首先通过PCR扩增内切葡聚糖酶eg基因,然后与pET-28a连接获得表达载体pET-28a::eg并转化至大肠杆菌(Escherichia coli)菌株BL21(DE3)中,用异丙基-β-D-硫代半乳糖苷(IPTG)诱导表达EG蛋白,最后用3,5-二硝基水杨酸(DNS)法测定重组内切酶的酶活力,分析其酶学性质。结果表明:成功构建表达载体pET-28a::eg,重组菌株E.coli BL21/pET-28a::eg在28℃用IPTG诱导14 h后纯化得到重组的EG蛋白,EG蛋白大小约为50 kDa,刚果红染色有明显水解圈。用DNS法测得EG的酶活为12.60 U·mL^(−1),滤纸总酶活为3.53 U·mL^(−1)。重组酶在不同底物的反应中,羧甲基纤维素钠为底物的酶活力最高,脱脂棉最低。重组酶的最适温度为40℃,最适pH为7.0。在此条件下,Ca^(2+)、Mg^(2+)、Fe^(2+)、K^(+)、Mn^(2+)等离子均可对重组蛋白EG的酶活力具有促进作用,Zn^(2+)可促进但差异不显著,而Hg^(2+)、Cu^(2+)对EG的酶活力具有抑制作用。本研究构建的重组内切酶菌株可以高效水解纤维素,为内切酶的工业应用奠定了基础。

橙黄小单孢菌(Micromonospora aurantiaca)几丁质酶基因的克隆、表达、鉴定及应用

从海洋微生物橙黄小单孢菌(Micromonosprra aurantiaca)的基因组DNA中克隆到一条新型的碳水化合物18家族几丁质酶基因Machi3,并成功在大肠杆菌(Escherichia coli)中表达。该酶的最适反应温度和pH分别为55℃和7.0,在低于55℃和pH 6.0~9.0范围内稳定性较好。镁离子(Mg^(2+))、钙离子(Ca^(2+))、吐温40(Tween 40)和吐温80(Tween 80)对MaChi3的酶活力有轻微的促进作用。该重组酶对α-几丁质、胶体几丁质、虾壳粉、不同脱乙酰度(50%~95%)的壳聚糖、淀粉及纤维素均具有水解活性,其中以胶体几丁质为底物时酶活力最高(2.24 U·mg^(−1))。由扫描电镜结果可知,几丁质经盐酸(HCl)预处理后得到的胶体几丁质纤维结构变得松散,更有利于MaChi3的水解作用。以胶体几丁质为底物时动力学参数K_(m)和V_(max)值分别为5.93 mg·mL^(−1)和8.58μmol·(min·mg)^(−1)。此外,胶体几丁质经MaChi3酶解后生成的主产物为N,N-二乙酰基壳二糖,产率(几丁质)为285.54 mg·g^(−1)。该酶展现出良好的酶学特性,为其在几丁质资源中的开发和应用奠定了基础。

群体感应淬灭酶AiiO的克隆表达及其发酵工艺优化

群体感应淬灭酶AiiO具有降解信号分子N-酰基高丝氨酸内酯(AHL)的活性,从而抑制病原菌的致病性。为提高AiiO表达量,构建了重组工程菌Escherichia coli BL21(DE3)-pET-28a(+)-aiiO,对其发酵生产AiiO过程中诱导温度、氮源质量浓度、诱导时机和乳糖添加量进行了优化。结果表明,在诱导温度25℃、蛋白胨20g/L和酵母粉10g/L、发酵初始时添加乳糖、乳糖添加量为5g/L的优化条件下,胞内可溶性AiiO的表达量达到374.26mg/L。

新型GH5家族多结构域纤维素酶的结构与功能研究

纤维素酶能够将纤维素转化为可发酵的糖类,为丰富纤维素酶的序列与结构资源、揭示纤维素酶结构与功能之间的关系,本研究对两个新型GH5家族多结构域内切纤维素酶TlCel5和ReCel5进行了克隆表达和酶学性质测定,并对其结构域开展了突变研究。序列和结构分析显示,Tlcel5和Recel5分别编码了655个和632个氨基酸,理论分子量分别为68.3 kD和65.9 kD,均包含了CBM1区、CD区、CBMX2区和一个未知结构域,这与以往报道的多数单一结构域或双结构域纤维素酶显著不同。为了解附加结构域对酶功能的影响效果,以ReCel5为研究对象,分别构建了N端CBM1结构域的截断突变体TM1,和C端未知结构域的截断突变体TM2。酶学性质分析显示,TlCel5和ReCel5的最适作用pH和最适作用温度分别为pH 3.0、50℃和pH 4.0、70℃,在50℃和70℃下能够保持良好的稳定性,并且对多种类型的纤维素类底物、半纤维素类底物表现出水解能力。虽然突变体TM1和TM2的酶学性质较野生型没有发生显著变化,但其对羧甲基纤维素钠、大麦葡聚糖、地衣多糖的水解比活值降低了23%-68%,由此说明,在多结构域酶中,附加结构域与酶的水解能力之间存在密切关系。

四氢嘧啶羟化酶的克隆表达、酶学性质及其在羟基四氢嘧啶合成中的研究

四氢嘧啶羟化酶(EctD)是双加氧酶超家族的重要成员,其底物四氢嘧啶和产物羟基四氢嘧啶的应用广泛,因此EctD在生物制造领域具有重要的应用价值。从来源于新疆盐湖的需盐色盐杆菌(Chromohalobacter salexigens)中获得四氢嘧啶羟化酶基因(ectD),并在E.coli BL21(DE3)中进行表达,对异源表达的EctD酶学性质进行研究。结果表明:EctD的最适温度是30℃、最适pH是7.5,在30℃、pH 6.5~8.0条件下具有较好的稳定性;Fe^(2+)、Ba^(2+)、Mn^(2+)、Mg^(2+)、Fe^(3+)和Ca^(2+)离子可增强EctD的酶活,而CO_(2)+、Zn^(2+)和Cu^(2+)离子明显抑制EctD的酶活;动力学参数为K_(m)=7.63 mmol/L、k_(cat)/K_(m)=1.011 L/(mmol·s)、V_(max)=6.75μmol/(mL·min)。在最适条件下,该酶以70 mmol/L四氢嘧啶为底物,催化反应25 h后,可生成68 mmol/L的羟基四氢嘧啶,底物转化率可达98%。本研究通过对EctD的表达和表征,为酶法合成羟基四氢嘧啶奠定基础。