关于酶促反应速度与酶促反应的初速度的教学

酶促反应速度是酶促反应动力学中的一个基本概念。一定条件下，酶催化反应的活力大小要由该反应条件下酶促反应速度来反映和确定：酶促反应速度越小，酶活力越小；反之，酶促反应速度越大，酶活力也越大。在研究底物浓度、酶浓度、温度、pH、激活剂、抑制剂等因素对酶活力的影响时，都必须测定酶促反应的速度。为了排除实验中存在的一些干扰，一个酶的酶促反应的速度要在酶促反应进行的初期测定，即测定所谓的酶促反应的初速度。在教学过程中，学生不易弄清楚酶促反应速度与酶促反应的初速度之间的关系。我们发现：当一般地问起酶反应速度在何时测定时，绝大多数学生都会回答在酶促反应的初期；而当问起酶促反应动力学中的v-[S]曲线(图1)上的酶促反应初速度在哪里和为什么时，却有相当一些学生指出在曲线的原点处做切线，切线的斜率就是；有的则指出是与1/2vmax相应的位置的速度值；个别的则指出是与vmax相应的位置的速度值。只有极少数学生指出曲线上的每一点相应的速度值都是酶促反应初速度所在。实际上，正确的答案应为曲线上的每一点相应的速度值均为该底物浓度[S]处的酶促反应初速度值。     

关于酶促反应速度与酶反应的初速度的教学

酶促反应速度是酶促反应动力学中的一个基本概念。一定条件下 ,酶催化反应的活力大小要由该反应条件下酶促反应速度来反映和确定 :酶促反应速度越小 ,酶活力越小 ;反之 ,酶促反应速度越大 ,酶活力也越大。在研究底物浓度、酶浓度、温度、ｐＨ、激活剂、抑制剂等因素对酶活力的影响时 ,都必须测定酶促反应的速度。为了排除实验中存在的一些干扰 ,一个酶的酶促反应的速度要在酶促反应进行的初期测定 ,即测定所谓的酶促反应的初速度。在教学过程中 ,学生不易弄清楚酶促反应速度与酶促反应的初速度之间的关系。我们发现 :当一般地问起酶反应速度…     

酶法转化DL-ATC合成L-半胱氨酸的酶促反应条件研究

目的:考察酶源保存方式、酶促反应时间、底物pH值、底物浓度、酶浓度、金属离子等因素对酶活力的影响。方法:以假单胞菌(Pseudomonassp.)TS1138为供试菌株,采用酸式茚三酮法测定L-半胱氨酸含量,研究了酶法转化DL-ATC合成L-半胱氨酸的酶促反应条件。结果:TS1138菌株中L-半胱氨酸脱巯基酶具有较高的活性,而且Mg2 、Mn2 、Fe2 、Zn2 、Cu2 等5种金属离子对DL-ATC水解酶酶系有不同程度的抑制,其中Cu2 对该酶系的抑制作用很大。结论:确定了TS1138菌株酶法转化DL-ATC合成L-半胱氨酸的最适酶促反应条件,为酶促反应动力学的研究奠定了基础。     

木枣试管苗叶片POD同功酶特性研究

以木枣试管苗叶片为材料,以愈创木酚为底物,研究其POD同功酶动力学,结果表明:木枣试管苗叶片POD同功酶酶促反应的最适pH值为5.0,最适温度范围为42～46℃之间,Km值为40.66 mmol/L,Vmax值为673.6U/s.gFW。在H2O2浓度为0.4%的反应体系中,反应3～18 min内测定酶活可获得较好的结果。     

脂肪酶在反相胶囊中的催化行为的研究

系统研究了脂肪酶在ＡＯＴ／水／异辛烷反应相胶囊中的催化行为。在一定条件下,反相胶囊中的酶反应的仍符合Ｍｉｃｈａｅｌｉｓ－Ｍｅｎｔｅｎ动力学原理,研究了含水量,底物浓度,ｐＨ,温度,溶剂的种类和表面活性剂浓度等对酶反应的影响。结果表明,酶活力与Ｒ值（水与表面活性剂的摩尔比值）有关。获得最大酶活力的条件是Ｒ＝１１,ｐＨ７．０,温度３２．５℃,橄榄油浓度为４０％。     

影响纳豆激酶酶促反应速度因素的研究

利用分光光度法对由纳豆菌发酵产生的纳豆激酶 (NK)进行了动力学性质的研究。以双倒数作图法 (L -B作图法 )求取Km。采用单因素试验法和正交试验法研究了底物浓度、酶浓度、温度、pH值对酶促反应速度的影响。结果表明该纳豆激酶的Km值为 3.4 98× 1 0 -6g·mL-1 ,当水解时间为 1 0min时 ,最适底物浓度为 1 6mg·mL-1 ,最适温度为 6 0℃ ,最适 pH为 8.0。     

粘质沙雷氏菌H3010发酵型D-乳酸脱氢酶基因的克隆表达、纯化及酶学性质研究

通过PCR技术从粘质沙雷氏菌H3010基因组DNA中扩增出该D-乳酸脱氢酶基因,连接至pET-28a（＋）表达载体,转入大肠杆菌BL21（DE3）中进行了重组表达,优化了酶纯化的条件,并对其酶学性质进行初步研究。结果表明,获得的该酶编码基因全长993bp,编码330个氨基酸,大小为37kDa。经优化表达及纯化条件后重组酶纯度可达90％。酶学性质研究发现,该重组酶最适反应温度为60℃,最适酶促反应pH为7．5（O．2mol／L磷酸盐缓冲液）,37℃下测得对底物丙酮酸的动力学参数Km=3．39mmol／L,Vmax=6．87mmol／（mg·min）,对辅酶NADH的动力学参数Km=1．43mmol／L,Vmax=1．61mmo]／（mg·min）。为酶法生产D-乳酸及利用代谢工程构建产D-乳酸的基因工程菌打下基础。     

混合溶剂系统对脂肪酶酯化活性和选择性的影响

目前非水介质中的酶促反应主要局限于单一有机溶剂系统。为使非水相酶反应顺利进行,所用反应介质一般必须满足２个条件：（１）具有较高的疏水性（ＬｏｇＰ值）［１］;（２）易于溶解底物。然而对于一些２芳基丙酸（如酮基布洛芬,以下简称酮洛芬）的酶促酯化反应［２...     

简单节杆菌转化氢化可的松的△-脱氢反应动力学I．简单节杆菌BY-2-13自由细胞转化氢化可的松的△-脱氢反应动力学

本文研究了简单节杆菌(Arthrobacter simplex) By-2-13转化氢化可的松为氢化泼尼松韵△一脱氢反应动力学。其中包括溶解底物的底物浓度对反应速度的影响,反应初速度与底物浓度的关系;固体悬浮液中底物总浓度对反应速度的影响,反应初速度与底物浓度的关系;酶量对反应的影响以及产物的抑制作用等。溶解底物和固体悬浮液底物的反应初速度与底物浓度的关系都符合简单米氏方程,米氏常数Km分别为0．33mg／mJ和29．41n,g／ml,而两者的反应过程曲线均与简单米氏方程不符。无论在较低或较高浓度的固体悬浮液底物转化过程中,产物对A’。脱氢反应都呈现抑制作用。由此建立了该反应的反应动力学模型及相应的动力学方程,井经线性化后回归得出反应的动力学参数。当反应时间小于‘(达到约85％的转化率所需要的时间)时,用此动力学方程拟合所得的数据与实验测定值相符。     

有机复合物H对纤维素CMC酶活的影响

采用3,5-二硝基水杨酸(DNS)为显色剂,CMC为底物,测定纤维素酶的酶活。考察了在不同的酶促反应温度、pH值、底物浓度、反应时间等反应条件下,有机复合物H对纤维素酶CMC酶活(CMCA)的影响。结果表明,有机复合物H对纤维素酶的CMCA活性有明显促进作用,且在不同条件下的促进效果有较大差异。     

A Unique Protease Cleavage Site Predicted in the Spike Protein of the Novel Pneumonia Coronavirus (2019-nCoV) Potentially Related to Viral Transmissibility

正Dear Editor,In December 2019, a novel human coronavirus caused an epidemic of severe pneumonia(Coronavirus Disease 2019,COVID-19) in Wuhan, Hubei, China(Wu et al. 2020; Zhu et al. 2020). So far, this virus has spread to all areas of China and even to other countries. The epidemic has caused 67,102 confirmed infections with 1526 fatal cases     

Curcuminoids as inhibitors of thioredoxin reductase: A receptor based pharmacophore study with distance mapping of the active site

Curcumin is the yellow pigment of turmeric that interacts irreversibly forming an adduct with thioredoxin reductase (TrxR), an enzyme responsible for redox control of cell and defence against oxidative stress. Docking at both the active sites of TrxR was performed to compare the potency of three naturally occurring curcuminoids, namely curcumin, demethoxy curcumin and bis-demethoxy curcumin. Results show that active sites of TrxR occur at the junction of E and F chains. Volume and area of both cavities is predicted. It has been concluded by distance mapping of the most active conformations that Se atom of catalytic residue SeCYS498, is at a distance of 3.56 from C13 of demethoxy curcumin at the E chain active site, whereas C13 carbon atom forms adduct with Se atom of SeCys 498. We report that at least one methoxy group in curcuminoids is necessary for interation with catalytic residues of thioredoxin. Pharmacophore of both active sites of the TrxR receptor for curcumin and demethoxy curcumin molecules has been drawn and proposed for design and synthesis of most probable potent antiproliferative synthetic drugs.     

Comparative morphology of the carpel in the Liliaceae: Hewardieae, Petrosavieae, and Tricyrteae

The young pistils in the melanthioid tribes, Hewardieae, Petrosavieae and Tricyrteae, are uniformly tricarpellate and syncarpous. They lack raphide idioblasts. All are multiovulate, with bitegmic ovules. The Petrosavieae are marked by the presence of septal glands and incomplete syncarpy. Tepals and stamens adhere to the ovary in the Hewardieae and the Petrosavieae but not in the Tricyrteae. Two vascular bundles occur in the stamens of the Hewartlieae and Tricyrtis latifolia. Ventral bundles in the upper part of the ovary of the Hewardieae are continuous with compound septal bundles and placental bundles in the lower part. Putative ventral bundles occur in the alternate position in the Tricyrteae and putative placental bundles in the opposite. position in the Petrosavieae. The dichtomously branched stigma in each carpel of the Tricyrteae is supplied by a bifurcated dorsal bundle.     

Enterovirus 71 3C proteolytically processes the histone H3 N-terminal tail during infection

Highlights
1. The N-terminal tail of histone H3 is specifically cleaved during EV71 infection.
2. Viral protease 3C is identified as a protease responsible for proteolytically processing the N-terminal H3 tail.
3. Our finding reveals a new epigenetic regulatory mechanism for Enterovirus 71 in virus-host interactions.     

Detection of EBV and HHV6 in the Brain Tissue of Patients with Rasmussen’s Encephalitis

Rasmussen’s encephalitis (RE) is a rare pediatric neurological disorder, and the exact etiology is not clear. Viral infection may be involved in the pathogenesis of RE, but conflicting results have reported. In this study, we evaluated the expression of both Epstein-Barr virus (EBV) and human herpes virus (HHV) 6 antigens in brain sections from 30 patients with RE and 16 control individuals by immunohistochemistry. In the RE group, EBV and HHV6 antigens were detected in 56.7% (17/30) and 50% (15/30) of individuals, respectively. In contrast, no detectable EBV and HHV6 antigen expression was found in brain tissues of the control group. The co-expression of EBV and HHV6 was detected in 20.0% (6/30) of individuals. In particular, a 4-year-old boy had a typical clinical course, including a medical history of viral encephalitis, intractable epilepsy, and hemispheric atrophy. The co-expression of EBV and HHV6 was detected in neurons and astrocytes in the brain tissue, accompanied by a high frequency of CD8⁺ T cells. Our results suggest that EBV and HHV6 infection and the activation of CD8⁺ T cells are involved in the pathogenesis of RE.     

Perinatal Vertical Transmission of Chikungunya Virus in Ruili,a Town on the Border between China and Myanmar

正Dear Editor,Chikungunya virus (CHIKV), an arbovirus in the family of Togaviridae, genus Alphavirus, is transmitted by the A.aegyptii or A. albopictus mosquito, and causes disease in humans characterized by fever, rash, and arthralgia (Silva and Dermody 2017; Suhrbier 2019). It was first reported in 1953 in Tanzania, and caused only a few outbreaks and sporadic cases in Africa and Asia in last century. However, in the epidemic in 2004, CHIKV acquired mutations that conferred enhanced transmission by the A. albopictus mosquito(Schuffenecker et al. 2006). Since then, it has successively caused outbreaks in Africa, the Indian Ocean, South East Asia, the South America, and Europe (Zeller et al. 2016).     

Development of a Novel Reverse Transcription Loop-Mediated Isothermal Amplification Method for Rapid Detection of SARS-CoV-2

In conclusion, the novel visual RT-LAMP assay is a simple, rapid, and sensitive approach for detection of SARS-CoV-2, and it is ready for application in primary care and community hospitals or health care centers, and even patients' own houses in response to the current SARS-CoV-2 epidemic because the assay does not require sophisticated equipment and skilled personnel. Furthermore, it is also ready to be used in fields for screening samples from wild animals and environments to facilitate the identification of potential intermediate hosts that mediate the cross-species transmission of SARS-CoV-2 from bats to humans.