漆树漆酶的催化氧化作用——Ⅳ.二茂铁及其衍生物的酶促氧化

In phosphate buffer-diethylene glycol monobutyl ether(DGBE), the oxidations of ferrocene and 15 derivatives were investigated in the presence of Rhus vernicifera laccase. The results showed that ferrocene and 11 derivatives can be oxidized. The mechanism of Laccase catalyzed oxidation of ferrocene was put forward.     

Four New Lariciresinol‐Based Lignan Glycosides from the Roots of Rhus javanica var. roxburghiana

The four new lariciresinol‐based lignan glycosides, (?)‐lariciresinol 4′‐(6″‐O‐feruloyl‐β‐D ‐glucopyranoside) ( 1 ), (?)‐lariciresinol 4′‐(4″,6″‐di‐O‐feruloyl‐β‐D ‐glucopyranoside) ( 2 ), 5,5′‐dimethoxylariciresinol 4′‐(4″,6″‐di‐O‐feruloyl)‐β‐D ‐glucopyranoside) ( 3 ), and 4‐O‐[α‐(1,2‐dihydroxyethyl)syringyl]‐5,5′‐dimethoxylariciresinol 4′‐(4″,6″‐di‐O‐feruloyl‐β‐D ‐glucopyranoside) ( 4 ), together with two known ones, lariciresinol 4′‐β‐D ‐glucopyranoside) ( 5 ) and tortoside B ( 6 ), were isolated from the BuOH extract of Rhus javanica var. roxburghiana roots, and their structures were established by means of various spectroscopic techniques.     

Sulfuretin protects against cytokine-induced ��-cell damage and prevents streptozotocin-induced diabetes

NF-κB activation has been implicated as a key signaling mechanism for pancreatic β-cell damage. Sulfuretin is one of the main flavonoids produced by Rhus verniciflua, which is reported to inhibit the inflammatory response by suppressing the NF-κB pathway. Therefore, we isolated sulfuretin from Rhus verniciflua and evaluated if sulfuretin could inhibit cytokine- or streptozotocin-induced β-cell damage. Rat insulinoma RINm5F cells and isolated rat islets were treated with IL-1β and IFN-γ to induce cytotoxicity. Incubation of cells and islets with sulfuretin resulted in a significant reduction of cytokine-induced NF-κB activation and its downstream events, iNOS expression, and nitric oxide production. The cytotoxic effects of cytokines were completely abolished when cells or islets were pretreated with sulfuretin. The protective effect of sulfuretin was further demonstrated by normal insulin secretion of cytokine-treated islets in response to glucose. Treatment of mice with streptozotocin resulted in hyperglycemia and hypoinsulinemia, which was further evidenced by immunohistochemical staining of islets. However, the diabetogenic effects of streptozotocin were completely prevented when mice were pretreated with sulfuretin. The anti-diabetogenic effects of sulfuretin were also mediated by suppression of NF-κB activation. Collectively, these results indicate that sulfuretin may have therapeutic value in preventing β-cell damage.     

Rhus laccase catalysis and product characterization of 1,2-dimethoxyphenol in organic solutions

Dimethoxyphenol was a widely used substrate in determination of laccases activity. It was surprised, however, that the products of it had not been completely determined until now. Studies were thus conducted on Rhus laccase （RL） and immobilized Rhus laccase （IRL）-catalyzed oxidation of 2,6-dimethoxyphenol （DMP） in water-organic solvent systems. Only one product, 3,3′,5,5′- tetramethoxy-1 ,1′-biphenyl-4,4′-diol （TMBP）, was produced by RL catalysis, and it was thoroughly characterized by FT-IR, NMR and GC-MS, etc.     

反胶团中漆树酶催化氧化性能与反应产物鉴定

研究了漆树酶在AOT/正辛烷/水反胶团中邻氨基苯酚的催化氧化性能。发现在40℃、pH=7.6、R=[H₂O]/[AOT]≈18的条件下,漆树酶的活力最高,在含水量较低的反胶团中较稳定。当R=6.2,于30℃保存15h活力仍保持82%;"水池"内存在的1.0×10^-3mol/L的Zn²⁺、Fe³⁺、Mg²⁺等离子对漆树酶有一定的抑制作用。漆树酶对邻氨基苯酚在反胶团和水溶液介质中,其主要氧化产物均为2-氨基-吩嗪-3-酮,但在反胶团中其反应产率比在水溶液中约高0.5倍。     

漆树漆酶的催化氧化作用 (ⅹⅢ)──Fe~(2+)离子对漆酶催化氧化反应的影响()

以５,６－二溴－２,３－二氰基氢醌为底物,在ｐＨ４．５０条件下,用分光光度法考察了ＦｅＳＯ４对漆树漆酶催化氧化反应的影响．结果表明,在本文实验条件下ＳＯ２－４离子对酶促反应的影响基本可以忽略,而Ｆｅ２＋离子对漆酶的催化氧化反应则有明显的竞争性抑制作用．研究证实,Ｆｅ２＋离子的抑制作用是通过它还原酶促反应的产物半醌自由基阴离子来实现的     

漆树漆酶的催化氧化作用──Ⅸ．含叔丁基的儿茶酚类底物的漆酶催化氧化

用分光光度法对６个含叔丁基的儿茶酚类底物在不同ＰＨ条件下的离解和漆酶催化氧化行为进行了考察，测定了它们在ＰＨ８．０时的反应速度常数．结果表明，叔丁基的疏水性较好地适应了漆酶对底物疏水程度的要求，使这类底物更容易为漆酶所包结；漆酶活性中心周围的酸性氨基酸残基中的ω－羧基阴离子所提供的ｐＨ环境和质子转移作用，促进了这类底物的离解，使这类底物能在远低于其一级离解所需ｐＨ的环境中进行反应．速度常数数据显示，取代基的疏水作用和取代基参与双齿配位的能力是影响这类底物反应速度的主要因素；在叔丁基的存在下，取代基的电子效应对这类底物的反应速度的影响变得不明显．     

漆树漆酶两种同工酶分离纯化与特性研究

应用柱层析和HPLC方法从漆树漆液中分离提纯漆酶的两种同工酶L1和L2 .两者均为低温酶 ,最适的温度分别为 2 0℃和 13℃ ,pH值分别为 6.7和 7.2 ,等电点分别为 8.6和 9.1.通过十二烷基硫酸钠 聚丙烯酰胺凝胶电泳 ,测得它们的分子量分别为 1.2× 10 5和 1.0 5× 10 5.两种酶均不能催化氧化间氨基苯甲酸 ,对 3 氨基酪氨酸等有很高的反应活性     

邻氨基苯酚与漆树漆酶反应的微量热法研究

在０．１ｍｏｌ／Ｌ的磷酸盐缓冲溶液（ｐＨ７．４）中，用微量热法测定了２９８．１５Ｋ时漆树漆酶与邻氨基苯酚反应的摩尔反应焓ΔｒＨｍ＝２５２．２１±３．５９ｋＪ／ｍｏｌ，米氏常数Ｋｍ＝７．７７×１０－３ｍｏｌ／Ｌ和表观一级反应速率常数ｋ１＝７．２３×１０－３ｓ－１，及此条件下邻氨基苯酚作底物时的漆酶活性值ＥＡ＝０．１９０（ＩＵ）。     

漆树漆酶催化2,6-二甲基酚的氧化反应

在0.1mol/L磷酸盐缓冲液中,漆树漆酶催化2,6-二甲基酚(DMP)氧化生成3,3'5.5'-四甲基-4,4'-二苯醌(TMDQ).pH8.0,温度40～50℃时酶促氧化DMP较快.DMP浓度在1.66×10^-4～9.92×10^-4mol/L时为一级反应,速率常数为3.57×10^-5s^-1,共存的二茂铁(Fc-H)能大大促进酶促氧化DMP的速度.提出了该反应可能的反应机理。