本文選題：酶催化反應(yīng) + 反應(yīng)機(jī)理　； 參考：《山東大學(xué)》2017年博士論文

【摘要】：酶是一切生命活動(dòng)的基礎(chǔ),幾乎所有細(xì)胞內(nèi)的代謝反應(yīng)都離不開酶的參與。正是由于酶的催化作用,生物代謝活動(dòng)中產(chǎn)生的物質(zhì)和能量才能滿足生物體的需求。由于酶具有傳統(tǒng)催化劑難以與之媲美的高效性和專一性以及催化反應(yīng)類型的多樣性,越來越多的酶已經(jīng)應(yīng)用到環(huán)境、藥物、工業(yè)等領(lǐng)域,可以預(yù)計(jì)未來會(huì)有更多的仿生催化劑和工程酶應(yīng)用到工業(yè)生產(chǎn)中。對(duì)酶的活性以及特異性機(jī)制的充分認(rèn)識(shí)不僅是了解生命活動(dòng)規(guī)律的基礎(chǔ),也是對(duì)酶進(jìn)行修飾改造的前提。但由于酶結(jié)構(gòu)和反應(yīng)機(jī)理的復(fù)雜性,僅靠實(shí)驗(yàn)方法難以對(duì)酶催化反應(yīng)機(jī)理進(jìn)行全面系統(tǒng)的了解。通過理論與計(jì)算化學(xué)方法可以從原子水平上揭示酶催化反應(yīng)的機(jī)理,對(duì)實(shí)驗(yàn)上難以觀測(cè)到的過渡態(tài)及中間體結(jié)構(gòu)進(jìn)行研究。目前,酶催化反應(yīng)的理論計(jì)算研究是酶催化領(lǐng)域的研究熱點(diǎn)之一。理論計(jì)算化學(xué)方法有很多,研究中需要依據(jù)要解決的問題選擇合適的方法。本論文主要利用量子力學(xué)和分子力學(xué)相結(jié)合的QM/MM方法對(duì)幾類金屬酶和糖苷酶的催化反應(yīng)機(jī)理進(jìn)行了較為系統(tǒng)的研究,確定了酶催化反應(yīng)的最可能路徑,得到了反應(yīng)中間體及過渡態(tài)的結(jié)構(gòu)和能量學(xué)信息,明確了酶活性中心殘基在催化過程中所起的作用,計(jì)算結(jié)果揭示了這些酶催化反應(yīng)的機(jī)制,對(duì)相關(guān)實(shí)驗(yàn)現(xiàn)象做出解釋,并能與現(xiàn)有的一些實(shí)驗(yàn)結(jié)果很好地吻合,同時(shí)也對(duì)實(shí)驗(yàn)結(jié)果做了進(jìn)一步的說明和補(bǔ)充,對(duì)相關(guān)酶反應(yīng)機(jī)理的理解解及酶應(yīng)用奠定了必要的理論基礎(chǔ)。主要研究工作如下:(1)AsqJ加雙氧酶催化喹啉生物堿合成機(jī)理的理論研究喹諾酮結(jié)構(gòu)是多種生物活性分子的骨架結(jié)構(gòu),4'-甲氧基綠霉素中的4-芳基喹啉片段存在于多種喹啉、喹諾酮生物堿中。近期研究表明曲霉屬真菌中的AsqJ酶在4'-甲氧基綠霉素的生物合成中起重要作用,并且AsqJ酶屬于非血紅素FeⅡ/酮戊二酸依賴加雙氧酶。2016年有人報(bào)道了 AsqJ與底物結(jié)合的晶體結(jié)構(gòu),并通過實(shí)驗(yàn)證實(shí)AsqJ酶通過催化兩個(gè)非耦合的去飽和化與環(huán)氧化反應(yīng)將底物轉(zhuǎn)化為4'-甲氧基綠霉素。基于得到的晶體結(jié)構(gòu),本文采用QM/MM方法對(duì)AsqJ催化的去飽和化反應(yīng)與環(huán)氧化反應(yīng)進(jìn)行了研究。計(jì)算結(jié)果表明,FeⅣ-O復(fù)合物需通過一個(gè)異構(gòu)化過程來引發(fā)整個(gè)催化反應(yīng),在去飽和化過程中,FeⅣ=O復(fù)合物奪取第一個(gè)氫的反應(yīng)是通過σ-通道進(jìn)行的,且該反應(yīng)是催化反應(yīng)的決速步驟,對(duì)應(yīng)的能壘為19.3 kcal/mol。在環(huán)氧化過程中,再次生成的FeⅣ=O復(fù)合物對(duì)去飽和化中間體的C=C進(jìn)行加氧反應(yīng),對(duì)應(yīng)的能壘為18.1kcal/mol。此外,基于底物N4位缺少甲基會(huì)導(dǎo)致催化反應(yīng)不能進(jìn)行的實(shí)驗(yàn)事實(shí),本文還考察了 N4-甲基對(duì)反應(yīng)的影響,計(jì)算發(fā)現(xiàn),N4-甲基的缺失并未直接影響FeⅣ=O的奪氫反應(yīng),可能是通過影響酮戊二酸的氧化反應(yīng)而對(duì)催化反應(yīng)產(chǎn)生影響。這些結(jié)果對(duì)進(jìn)一步理解非血紅素加雙氧酶的反應(yīng)機(jī)理以及喹啉生物堿的生物合成路徑提供了堅(jiān)實(shí)的理論基礎(chǔ)。(2)咪唑啉酮酸酶催化機(jī)理的理論研究組氨酸在生物體內(nèi)的降解受到嚴(yán)格控制,自然界中組氨酸的降解路徑從原核生物到真核生物都是高度保守的。咪唑啉酮酸酶(HutI,EC3.5.2.7)是生物體中組氨酸降解路徑中的第三種酶,該酶催化4-咪唑啉酮-5-丙酸(IPA)水解生成L-谷氨酸。前人依據(jù)實(shí)驗(yàn)結(jié)果建議了大致的反應(yīng)機(jī)理,但關(guān)于該酶的底物選擇性、水分子活化機(jī)制等問題依然沒有得到解決。本文使用QM/MM方法對(duì)IPA的(S)-和(R)-對(duì)映體的同分異構(gòu)體SIPA-1,SIPA-2,RIPA-1和RIPA-2的催化反應(yīng)進(jìn)行了研究。計(jì)算結(jié)果表明,起水解作用的水分子(與鋅配位的水分子)是E252殘基通過橋連水分子來活化的,且發(fā)生在與底物與酶結(jié)合之前。在底物結(jié)合之后,活化通道就會(huì)被底物阻斷;另外兩個(gè)殘基(D324,H272)不能活化水分子。HutI只能將IPA的兩個(gè)(S)-對(duì)映體中的SIPA-1轉(zhuǎn)換成L-谷氨酸,其能量勢(shì)壘為16.6 kcal mol-1。而SIPA-2的轉(zhuǎn)換能壘則為21.9 kcal mol-1。然而,對(duì)于兩個(gè)(R)-對(duì)映體來說,RIPA-1能壘更高一些(21.8kcalmol-1),RIPA-2在活性位點(diǎn)的結(jié)合作用比sIPA-2更弱。基于計(jì)算結(jié)果,SIPA-1是HutI最佳的底物,而sIPA-2的水解斷鍵可能需要先轉(zhuǎn)化為SIPA-1才能發(fā)生。通過計(jì)算我們給出了 HutI催化反應(yīng)的細(xì)節(jié),明確了 HutI酶的底物選擇性,為深入了解L-組氨酸在哺乳動(dòng)物和細(xì)菌中的生物降解路徑提供了理論基礎(chǔ)。(3)氮-乙酰葡糖胺糖苷水解酶催化機(jī)理的理論研究糖類在生物體內(nèi)有許多重要的作用,它除了可以作為結(jié)構(gòu)組分以及提供生物體必要的能量外,還通過對(duì)肽聚糖的修飾在免疫響應(yīng)中扮演重要的角色。肽聚糖(PG)的代謝路徑對(duì)于細(xì)菌的生長(zhǎng)至關(guān)重要。β-氮-乙酰葡糖胺糖苷酶(NagZ)是肽聚糖代謝路徑中一種重要蛋白酶。依據(jù)氨基酸順序以及二級(jí)結(jié)構(gòu)的分類,NagZ酶屬于糖苷水解酶第三家族(GH3)。然而,最近的實(shí)驗(yàn)研究發(fā)現(xiàn)NagZ酶是糖苷磷酸化酶而不是糖苷水解酶。為進(jìn)一步從原子水平上探究NagZ酶的催化機(jī)理,本文用QM/MM方法對(duì)來源于枯草芽孢桿菌的NagZ酶(BsNagZ)的催化反應(yīng)進(jìn)行了研究。計(jì)算結(jié)果表明,整個(gè)催化循環(huán)的決速步是糖基化反應(yīng),該結(jié)論與實(shí)驗(yàn)研究相符。糖基化反應(yīng)對(duì)應(yīng)的能壘為19.3 kcal/mol,該能壘與實(shí)驗(yàn)上通過使用類似底物進(jìn)行反應(yīng)動(dòng)力學(xué)實(shí)驗(yàn)預(yù)測(cè)的自由能能壘(16.4 kcal/mol)近似。對(duì)于去糖基化過程,對(duì)水解機(jī)理和磷酸化機(jī)理的對(duì)比研究發(fā)現(xiàn),磷酸化對(duì)應(yīng)的能壘為(1.8kcal/mol),較水解路徑的能壘低(17.7kcal/mol),這一結(jié)果支持了之前關(guān)于NagZ酶為磷酸化糖苷酶的結(jié)論。研究還發(fā)現(xiàn),不論是在糖基化還是去糖基化過程中都有類似于羰基正離子過渡態(tài)的參與,活性中心底物的構(gòu)型變化對(duì)反應(yīng)有較大影響,以上理論計(jì)算與實(shí)驗(yàn)預(yù)測(cè)吻合。這些計(jì)算結(jié)果有助于深入理解NagZ酶的催化機(jī)理,有助于針對(duì)GH3家族β-1,4葡糖胺苷酶的抑制劑的研發(fā)。(4)α-1,4-糖苷解酶催化機(jī)理的理論研究α-1,4-糖苷裂解酶(GLases,EC 4.2.2.13)是糖苷水解酶家族中獨(dú)特的一員,它可以特異性的催化糖原、淀粉以及低聚麥芽糖中α-1,4-糖苷鍵的斷裂,從多糖的非還原端斷開糖苷鍵生成1,5-脫水-D-果糖。之前的研究表明,GLases屬于構(gòu)型保持型糖苷裂解酶,在催化反應(yīng)中涉及到糖苷酶中間體的形成,整個(gè)催化循環(huán)包括羰基化和去糖基化/消除兩個(gè)過程�；谧钚掳l(fā)表的晶體結(jié)構(gòu)(2X21),本文用QM/MM方法對(duì)GLases進(jìn)行了研究。結(jié)果表明,整個(gè)催化循環(huán)包含五步基元反應(yīng)。首先天冬氨酸D665做為路易斯酸,向糖苷氧提供一個(gè)質(zhì)子,同時(shí)糖苷鍵發(fā)生斷裂。然后去質(zhì)子化的D553殘基進(jìn)攻端基碳形成糖苷酶中間體,該中間體的存在在實(shí)驗(yàn)上已得到了論證。在此糖基化過程中普通的保持型糖苷酶是通過協(xié)同機(jī)理進(jìn)行的,而該酶的糖基化過程是分步進(jìn)行的。對(duì)于去糖基化/消除反應(yīng),我們考慮了反應(yīng)是在麥芽三糖離開活性位點(diǎn)前發(fā)生的或在麥芽三糖離開活性位點(diǎn)之后發(fā)生的兩種情況。計(jì)算結(jié)果表明,麥芽三糖的離去有利于去糖基化/消除反應(yīng)的進(jìn)行,在這步反應(yīng)中,去質(zhì)子化的D553殘基可以作為催化堿來奪取糖環(huán)上C2位置的質(zhì)子,并且去糖基化/消除反應(yīng)中的奪質(zhì)子反應(yīng)是整個(gè)催化反應(yīng)的決速步,兩種情況對(duì)應(yīng)的勢(shì)壘分別是20.59和18.53 kcal/mol。糖苷化過程通過D665殘基對(duì)糖苷氧的質(zhì)子化來引發(fā)反應(yīng),糖苷裂解酶的糖基化過程是通過分步反應(yīng)機(jī)理發(fā)生的,并且去糖基化/消除反應(yīng)是整個(gè)催化循環(huán)的決速步,這些研究結(jié)果對(duì)于理解α-1,4糖苷酶的催化機(jī)理提供了理論依據(jù),并對(duì)該類酶的工業(yè)應(yīng)用提供了理論基礎(chǔ)。本論文特色和創(chuàng)新之處弄清酶催化反應(yīng)的機(jī)理不僅有助于理解這些蛋白酶的生物學(xué)功能,也是對(duì)這一高效生物催化劑進(jìn)行工業(yè)應(yīng)用的重要前提。本論文采用理論化學(xué)方法對(duì)兩類金屬酶(AsqJ加雙氧酶、咪唑啉酮酸酶)以及兩類糖苷酶(BsNagZ酶、α-1,4糖苷裂解酶)的催化反應(yīng)進(jìn)行了系統(tǒng)深入的研究,取得了以下重要成果:(1)系統(tǒng)地闡明了 AsqJ加雙氧酶催化合成喹啉生物堿的機(jī)制,確定了在AsqJ的催化反應(yīng)中FeⅣ-O的異構(gòu)化是催化反應(yīng)的必需步驟,FeⅣ-O復(fù)合物的奪氫反應(yīng)遵循σ-通道機(jī)理,分步進(jìn)行的環(huán)氧化反應(yīng)和去飽和化過程都經(jīng)歷碳自由基中間體,對(duì)AsqJ不能催化N4-位不含有甲基的底物類似物的本質(zhì)原因進(jìn)行了探討。(2)預(yù)測(cè)了咪唑啉酮酸酶(HutI)對(duì)四種4-咪唑啉酮-5-丙酸(IPA)的同分異構(gòu)體的催化活性,闡明了 HutI對(duì)底物的選擇性本質(zhì),解決了實(shí)驗(yàn)上存在爭(zhēng)議的水分子水分子的活化機(jī)制問題,明確了反應(yīng)中鋅離子的作用。(3)從理論闡明了 β-氮-乙酰葡糖胺糖苷酶(NagZ)酶屬于磷酸化酶而不是水解酶,即去糖基化過程遵循磷酸化機(jī)理,不論是糖基化還是去糖基化過程中都經(jīng)過類似于羰基正離子過渡態(tài),明確了對(duì)該酶底物扭曲其關(guān)鍵作用的殘基,驗(yàn)證了糖基化過程是整個(gè)催化循環(huán)的決速步驟。(4)闡明了 α-1,4糖苷裂解酶的催化機(jī)理,給出了催化反應(yīng)的的最可能路徑,明確了糖基化過程是通過分步反應(yīng)機(jī)理發(fā)生的,去糖基化/消除反應(yīng)是整個(gè)催化循環(huán)的決速步驟,并且驗(yàn)證了實(shí)驗(yàn)上預(yù)測(cè)的反應(yīng)中涉及到碳正離子中間體以及實(shí)驗(yàn)上提出的反應(yīng)中的親核試劑做為去糖基化過程中催化堿的機(jī)理。
[Abstract]:Enzymes are the basis of all life activities, and the metabolic reactions within almost all cells are inseparable from the involvement of enzymes. It is due to enzyme catalysis that the substances and energy produced in biological metabolism can meet the needs of the organism. The enzyme has the incomparable efficiency and specificity as well as the type of catalytic reaction because of the enzyme's traditional catalyst. More and more enzymes have been applied to the fields of environment, medicine and industry, and more biomimetic catalysts and engineering enzymes can be expected to be applied to industrial production in the future. The full understanding of the activity and specific mechanism of the enzymes is not only the basis for understanding the law of life activities, but also the prerequisite for the modification and modification of the enzyme. Because of the complexity of the enzyme structure and reaction mechanism, it is difficult to fully and systematically understand the mechanism of enzymatic reaction only by experimental methods. Through theoretical and computational methods, the mechanism of enzymatic reaction can be revealed from the atomic level, the structure of the transition state and intermediate structure, which is difficult to be observed in the experiment, is studied. At present, the enzyme catalyzed reaction is used. Theoretical calculation research is one of the hotspots in the field of enzyme catalysis. There are many theoretical computational methods. In this paper, we need to choose the appropriate method according to the problems to be solved. This paper mainly uses the QM/MM method combining quantum mechanics and molecular mechanics to make a more systematic mechanism for the catalytic reaction of several kinds of metal enzymes and glucosidase. The most likely path of enzyme catalysis is determined. The structure and energy information of the reaction intermediate and transition state are obtained. The role of the enzyme active center residues in the catalytic process is clarified. The results of the calculation reveal the mechanism of these enzyme catalytic reactions, explain the related testing phenomena, and can be used with some of the existing experiments. The results are in good agreement, and the experimental results are further explained and supplemented, and the necessary theoretical basis for the understanding of the mechanism of the enzyme reaction and the application of the enzyme are laid. The main research work is as follows: (1) the theoretical study of the synthesis mechanism of quinoline alkaloids by AsqJ and dioxygenase Frame structure, 4- aryl quinoline fragments in 4'- methoxy green mycin exist in a variety of quinoline and quinolone alkaloids. Recent studies have shown that the AsqJ enzyme in Aspergillus fungi plays an important role in the biosynthesis of 4'- methoxy green mycin, and the AsqJ enzyme is a non heme Fe II / ketopamyl acid dependent plus dioxygen enzyme.2016 reported in Asq. The crystal structure of J combined with the substrate has been proved by experiments to prove that the AsqJ enzyme is converted to 4'- methoxy green myxomycin by catalyzing two uncoupled desaturation and epoxidation. Based on the obtained crystal structure, the QM/MM method is used to study the desaturation and epoxidation of AsqJ catalyzed by AsqJ. The calculation results show that F The e IV -O complex needs to initiate the whole catalytic reaction through a isomerization process. During the desaturation, the reaction of the Fe IV =O complex to capture the first hydrogen is carried out through the sigma channel, and the reaction is a quick step of the catalytic reaction. The corresponding energy barrier is 19.3 kcal/mol. in the process of epoxidation, and the Fe IV =O complex is regenerated again. The oxygen reaction to the C=C of the desaturation intermediate, the corresponding energy barrier is 18.1kcal/mol., and the absence of methyl on the substrate N4 will lead to the experimental fact that the catalytic reaction can not be carried out. The effect of the N4- methyl on the reaction is also investigated. It is found that the deletion of N4- methylate does not directly affect the hydrogen capture reaction of the Fe IV =O, which may be passed through Influence of the oxidation of ketopentandiacid on the catalytic reaction. These results provide a solid theoretical basis for further understanding of the reaction mechanism of non heme and dioxygenase and the biosynthesis path of quinoline alkaloids. (2) the theoretical research of the mechanism of imidazolinase catalyzed by histidine is strict in the degradation of the organism. Control, the degradation pathway of histidine in nature is highly conserved from prokaryotes to eukaryotes. HutI (EC3.5.2.7) is the third enzyme in the histidine degradation pathway in organism, which catalyzes the hydrolysis of 4- imidazolinone -5- propionic acid (IPA) to produce L- glutaric acid. However, the substrate selectivity of the enzyme and the activation mechanism of water molecules are still not solved. In this paper, the catalytic reaction of IPA (S) - and (R) - enantiomers SIPA-1, SIPA-2, RIPA-1 and RIPA-2 in enantiomers was studied by QM/MM method. The 252 residue is activated by a bridge with water molecules and occurs before the substrate is combined with the enzyme. After the substrate binding, the activation channel is blocked by the substrate; the other two residues (D324, H272) can not activate the water molecule.HutI only to convert the SIPA-1 in the enantiomer to the L- Glutamic acid, and the energy barrier of the IPA is 16.6 kcal mol-1. and S. The conversion energy barrier of IPA-2 is 21.9 kcal mol-1., however, for two (R) enantiomers, RIPA-1 can be higher (21.8kcalmol-1), RIPA-2 is weaker in the binding of the active site than sIPA-2. Based on the calculation, SIPA-1 is the best substrate for HutI, and sIPA-2 water disconnection may need to be converted to SIPA-1 to occur first. The details of the HutI catalytic reaction are given and the substrate selectivity of the HutI enzyme is clarified. The theoretical basis for understanding the biodegradation path of L- histidine in mammals and bacteria is provided. (3) the theoretical study of the catalytic mechanism of N-acetylglucosamine hydrolase The metabolic pathway of peptidoglycan (PG) is important for the growth of the bacteria. Beta n-acetylglucosinase (NagZ) is an important protease in the pathway of peptidoglycan metabolism. The NagZ enzyme belongs to the third family of glucoside hydrolase (GH3). However, the recent experimental study found that the NagZ enzyme is glucoside phosphorylase instead of glucoside hydrolase. In order to further explore the catalytic mechanism of NagZ enzyme from the atomic level, the QM/MM method has been used in QM/MM to promote the NagZ enzyme (BsNagZ) derived from Bacillus subtilis (BsNagZ). The results show that the quick step of the whole catalytic cycle is a glycosylation reaction, which is consistent with the experimental study. The corresponding energy barrier of the glycosylation reaction is 19.3 kcal/mol, and the energy barrier is similar to the free energy barrier (16.4 kcal/mol) predicted by the experimental kinetic experiment by using similar substrates. In the process of glycosylation, a comparative study of the mechanism of hydrolysis and phosphorylation found that the corresponding energy barrier of phosphorylation was (1.8kcal/mol), which was lower than the energy barrier of the hydrolytic pathway (17.7kcal/mol). This result supported the previous conclusion that the NagZ enzyme was phosphorylated glucosidase. With the participation of the transition state of carbonyl positive ions, the configuration changes of the active center substrates have great influence on the reaction, and the theoretical calculation coincides with the experimental prediction. These results are helpful to understand the catalytic mechanism of NagZ enzyme and help the development of the inhibitor of the GH3 family beta Glucosaminidase. (4) the alpha -1,4- glycosidase catalytic machine The theoretical study of the theoretical study of alpha -1,4- glycoside lyase (GLases, EC 4.2.2.13) is a unique member of the glycoside hydrolase family. It can specifically catalyze the fracture of glycosides, starch and the alpha -1,4- glycosides of oligosaccharides, and disconnect the glycosides from the non reductive ends of the polysaccharides to produce 1,5- dehydrated -D- fructose. Previous studies have shown that GLases belongs to the configuration. The retention type glucoside lyase is involved in the formation of glucosidase intermediates in the catalytic reaction. The whole catalytic cycle includes carbonylation and glycosylation / elimination of two processes. Based on the latest published crystal structure (2X21), the QM/MM method is used to study GLases. The results show that the whole catalytic cycle contains five step reaction. Aspartate D665 is a Lewis acid, which provides a proton to glycoside oxygen, while the glycosidic bond breaks. Then the protonated D553 residues attack the end group carbon to form a glycosidase intermediate. The existence of the intermediate has been demonstrated experimentally. In this glycosylation process, the common preserved glucosidase is carried out through synergistic mechanism. The glycosylation process is carried out step by step. For the deglycosylation / elimination reaction, we consider that the reaction occurs before the malt three sugar leaves the active site or after the malt three sugar leaves the active site. The results show that the departure of the malt three sugar is beneficial to the deglycosylation / elimination of the reaction, in this case, the deglycation of malt three sugar is beneficial to the deglycosylation / elimination reaction. In the step reaction, the deprotonated D553 residue can be used as a catalytic base to capture protons on the C2 position on the sugar ring, and the protonic reaction in the deglycosylation / elimination reaction is the quick step of the whole catalytic reaction. The corresponding potential barriers in the two cases are 20.59 and 18.53 kcal/mol. Glucosidation, respectively, by the protonation of glucoside oxygen through the D665 residue. The glycosylation process of glucoside lyase occurs by step reaction mechanism, and glycosylation / elimination reaction is a quick step for the whole catalytic cycle. These results provide a theoretical basis for understanding the catalytic mechanism of alpha -1,4 glucosidase, and provide a theoretical basis for the industrial application of this kind of enzyme. Making clear the mechanism of enzymatic reaction is not only helpful to understand the biological function of these proteases, but also an important prerequisite for the industrial application of this highly efficient biocatalyst. This paper uses the theoretical chemistry method for two kinds of metal enzymes (AsqJ plus dioxygenase, imidazolidase) and the two kind of glucosidase (BsNagZ enzyme, alpha -1,4 sugar). The catalytic reaction of glycoside lyase has been systematically studied, and the following important achievements have been obtained: (1) the mechanism of AsqJ and dioxygenase catalyzed synthesis of quinoline alkaloids is systematically clarified. The isomerization of Fe IV -O in the catalytic reaction of AsqJ is a necessary step for catalytic reaction, and the hydrogen capture reaction of Fe IV -O complex follows the sigma channel mechanism. The cyclic oxidation reaction and desaturation process all undergo carbon free radical intermediates, and the essential reason for AsqJ's inability to catalyze the substrate analogues without methyl N4- is discussed. (2) the catalytic activity of imidazolininase (HutI) on the isomers of the four 4- imidazolinone -5- propionic acid (IPA) is predicted, and the HutI pair is clarified. The selective nature of the substance has solved the activation mechanism of water molecules that have been disputed experimentally and clarified the effect of zinc ions in the reaction. (3) it is explained from theory that beta nitrogen acetyl glucosidase (NagZ) enzyme belongs to phosphorylase rather than hydrolase, that is, the process of glycosylation follows phosphorylation mechanism, whether glycosylation or In the process of deglycosylation, the transition state similar to carbonyl positive ion is passed, and the key effect on the enzyme substrate is identified. The glycosylation process is the quick step of the whole catalytic cycle. (4) the catalytic mechanism of the alpha -1,4 glycoside lyase is clarified, the most possible path of the catalytic reaction is given, and the glycosylation process is clearly defined. It is by step reaction mechanism that de glycosylation / elimination reaction is the quick step of the whole catalytic cycle, and it is verified that the experimental reaction involves the carbon cation intermediate and the nucleophilic reagents in the experimental reaction as the mechanism of the catalytic alkali in the process of glycosylation.

【學(xué)位授予單位】：山東大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2017
【分類號(hào)】：O629.8;O643.31

【參考文獻(xiàn)】

相關(guān)期刊論文 前1條

1 劉文劍;;新一代相對(duì)論量子化學(xué)方法[J];中國(guó)基礎(chǔ)科學(xué);2007年02期

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本文編號(hào)：1778468