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1.
Aspartate ammonia lyase (Asp) is one of three types of ammonia lyases specific for aspartate or its derivatives as substrates, which catalyzes the reversible reaction of l-aspartate to yield fumarate and ammonia. In this paper, the catalytic mechanism of Asp has been studied by using combined quantum-mechanical/molecular-mechanical (QM/MM) approach. The calculation results indicate that the overall reaction only contains two elementary steps. The first step is the abstraction of Cβ proton of l-aspartate by Ser318, which is calculated to be rate limiting. The second step is the cleavage of CαN bond of l-aspartate to form fumarate and ammonia. Ser318 functions as the catalytic base, whereas His188 is a dispensable residue, but its protonation state can influence the active site structure and the existing form of leaving amino group, thereby influences the activity of the enzyme, which can well explain the pH dependence of enzymatic activity. Mutation of His188 to Ala only changes the active site structure and slightly elongates the distance of Cβ proton of substrate with Ser318, causing the enzyme to remain significant but reduced activity. 相似文献
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运用“单一组分缺失法”研究了18种氨基酸,11种维生素,8种微量元素,4种嘌呤与嘧啶对大肠杆菌A5发酵产转氨酶的影响。结果表明,L-甲硫氨酸是菌体生长与产酶所必需的物质,L-缬氨酸、L-异亮氨酸和L-谷氨酸分别对菌体生长和酶转化得率的提高有显著的促进作用。在此基础上构建了一个改良的合成培养基,其组成为(g/L):葡萄糖20,(NH4)2SO45,MgSO40.5,NaCl0.5,K2HPO40.5,KH2PO40.5,氨基酸混合液(包括L-Met、L-Val、L-Ile、L-Glu)0.6,pH7.2,所产转氨酶的转化得率达到72.4%。 相似文献
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探讨D-柠檬烯(D-limonene)对大鼠酒精性肝损伤脂质代谢紊乱的保护作用及可能作用机制,利用持续酒精灌胃的方法建立大鼠酒精肝损伤模型,分为A、B、C、D、E、F、G共7 组。A组为空白对照组,每日给予蒸馏水灌胃,前2 周8 mL/(kg·d),后4 周12 mL/(kg·d);B组为酒精模型组,每日灌胃体积分数为50%的乙醇,前2 周8 mL/(kg·d),后4 周12 mL/(kg·d);C、D、E组分别为D-柠檬烯低、中、高剂量组,每日分别灌胃D-柠檬烯100、200、400 mL/(kg·d),其中D-柠檬烯与A、B组等量的50%的乙醇混合后灌胃;F组为水和D-柠檬烯空白高剂量组,每日给予D-柠檬烯400 mL/(kg·d);G组为甘利欣药物对照组,灌胃量200 mL/(kg·d)。HE染色和电镜观察肝组织形态结构和肝组织超微结构的变化,测定血清谷丙转氨酶(alanine transaminase,ALT)、谷草转氨酶(aspartate transaminase,AST)、碱性磷酸酶(phosoporic acid,ALP)、胆碱酯酶(cholinesterase,CHE)、甘油三酯(triglyceride,TG)、胆固醇(cholesterol,CHO)、低密度脂蛋白胆固醇(low densitylipoprotein-cholesterol,LDL-C)水平。结果电镜下观察到A组肝细胞结构正常,核呈圆形或椭圆,线粒体形态正常。B组肝细胞次级溶酶体数量增加,线粒体形状不规则,脂滴多。C组可见少量脂滴,高尔基体正常,线粒体清楚。D组少量脂滴,胆小管有内容物,线粒体正常。E组线粒体高尔基体正常,少量脂滴,核圆。F组细胞器无异常,少量脂滴。G组少量脂滴,偶见溶酶,体线粒体正常。B组大鼠血清ALT、AST、ALP、CHE、TG、CHO、LDL-C均高于空白对照组,差异显著(P<0.05);F组大鼠血清所测各指标与空白对照组无明显差异;而D-柠檬烯低、中、高剂量干预组和酒精模型组比较,血清所测各指标水平均有不同程度地降低,其中D-柠檬烯中、高剂量干预组血清所测各指标水平明显低于酒精模型组,差异显著(P<0.05)。结论:过量酒精摄入引起的肝组织超微结构病理损伤与升高血清ALP、CHE、ALT、AST、TG、CHO、LDL-C水平,在D-柠檬烯干预下有所减轻和降低。因此,D-柠檬烯可调节过量酒精摄入造成的脂质代谢紊乱。 相似文献
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Alanine : glyoxylate aminotransferase is one of three different enzymes used for glycine synthesis in Saccharomyces cerevisiae. The open reading frame YFL030w (named AGX1 in the following), encoding this enzyme, was identified by comparing enzyme specific activities in knockout strains. While 100% activity was detectable in the parental strain, 2% was found in a YFL030w::kanMX4 strain. The ORF found at that locus was suspected to encode alanine : glyoxylate aminotransferase because its predicted amino acid sequence showed 23% identity to the human homologue. Since the YFL030w::kanMX4 strain showed no glycine auxtrophic phenotype, AGX1 was replaced by KanMX4 in a Delta GLY1 Delta SHM1 Delta SHM2 background. These background mutations, which cause inactivation of threonine aldolase, mitochondrial and cytosolic serine hydroxymethyltransferase, respectively, lead to a conditional glycine auxotrophy. This means that growth is not possible on glucose but on ethanol as the sole carbon source. Additional disruption of AGX1 revealed a complete glycine auxotrophy. Complementation was observed by transformation with a plasmid-encoded AGX1. 相似文献
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The Khapra beetle, Trogoderma granarium Everts, is one of the most important pests of grains which rapidly infests durable stored products in hot and dry conditions. In the current study, effects of omit ten varieties of barley (Abidar, Bahman, Line20, Line22, Line30, Lisivi, Lokht11, Makuyi, Sahand and Sahraa) were determined on digestive enzymes and protein metabolsim of T. granarium larvae under laboratory conditions as 33 ± 1 °C, 65 ± 5% RH and photoperiod of 14:10 (L: D) h. The highest and the lowest activities of α-amylase were observed in T. granarium larvae fed on Line30 and Lisivi varieties, respectively but the glucosidases showed the highest activities followed by feeding on Lokht 11. Also, the latter variety caused the highest lipase activity in the larvae while Abidar, Line20, Lisuei and Sahand imposed the lowest lipase activity. The highest activities of serine proteases including trypsin, chymotrypsin and elastase were detected in the larvae fed on Line 30 but the two exopeptidases, amino- and carboxypeptidases, showed the highest activities when the larvae fed on Lisuei. All the three aminotransferses had the highest activities in the larvae fed on Lokht 11 as the related individuals contained the maximum amount of protein compared to other ones. Results of the current study highlighted Line30 as the most suitable variety to be digested by serine proteases and α-amylase but Lokht11 is appropriately digested by glucosidases and lipase which emboss their susceptibilities to T. granarium. Our findings on digestion and protein metabolism imply on susceptibility of varieties Line30 and Lokht11 to T. granarium larvae. 相似文献
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Yi-Jen Fang Chih-Hsien Chiu Yuan-Yen Chang Chung-Hsi Chou Hui-Wen Lin Ming-Feng Chen Yi-Chen Chen 《Food research international (Ottawa, Ont.)》2011,44(9):3105-3110
Chronic alcohol consumption or alcohol abuse is the main cause of alcoholic steatohepatitis or further cirrhosis. This study was to exam if the antioxidant capacity and alcohol metabolism in livers of chronic alcohol-fed rats were improved by supplementing taurine (Tau). Rats were randomly divided into four groups with five times per week of treatment: 1) isocaloric solution; 2) 3 g alcohol/kg BW/day; 3) 3 g alcohol/kg BW/day + 1 g taurine (Tau)/kg BW/day; and 4) 3 g alcohol/kg BW/day + 2 g Tau/kg BW/day. A 6-week alcohol consumption resulted in lower (p < 0.05) body weight gain and self-antioxidant capacities, as well as increased (p < 0.05) liver size, serum/hepatic lipids, and AST and ALT values. However, alcohol-fed rats co-treated with Tau have decreased (p < 0.05) liver lipid levels via increasing fecal lipid output and cholesterol metabolism. Besides, co-treatment of Tau also enhanced (p < 0.05) self-antioxidant capacities and alcohol metabolism in livers via enhancing GSH contents, CAT, GSH-Px, ADH, and ALDH activities, but decreasing MDA contents. In a histological examination of rat liver, microvesicular steatosis and necrotic cells were observed in alcohol-fed rats without Tau while largely suppressed microvesicular steatosis and no necrotic cells were observed in alcohol-fed rat supplemented with Tau. Therefore, Tau could be an effective hepatoprotective agent against alcohol-induced damage via enhancing self-antioxidant capacity and alcohol metabolism. 相似文献
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本研究对韩国传统饮品太明清(TMC)对扑热息痛所致小鼠肝损伤的保护作用进行了研究,ICR小鼠连续14 d灌胃给予低(100 mg/kg)、中(250 mg/kg)、高(500 mg/kg)三个剂量的太明清及阳性药物水飞蓟素(100 mg/kg)后,腹腔注射扑热息痛(800mg/kg)建立动物急性肝损伤模型,动物处死后取血液和脏器测定各项指标。相对于模型对照组,太明清实验组的肝指数明显降低。三个剂量的太明清均明显降低血清谷丙转氨酶(ALT),谷草转氨酶(AST),碱性磷酸酶(ALP),甘油三酯(TG),尿素氮(BUN)水平,提高血清总胆固醇(TC),白蛋白(ALB)水平(p0.05)。且三个剂量呈现了一定的量效关系。其中太明清高剂量组对小鼠肝损伤的保护效果最佳,仅次于阳性药物水飞蓟素组(p0.05)。另外,从小鼠肝脏病理图来看,相对于模型对照组,太明清实验组对炎症及肝细胞坏死有明显改善。可见太明清对扑热息痛所致小鼠肝损伤具有较好的保护作用。 相似文献
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本研究基于电子克隆获得的大豆GmASADH基因eDNA序列,根据其编码区设计特异引物,以大豆品种小鹦哥豆总RNA为模板,通过RT—PCR获得了约1130bp的eDNA片段,T/A克隆后进行序列测定。测序结果显示,GmASADH基因家族有两个成员,命名为GmASADHI(FJ581425)和GmASADI-12(HM015631)。GmASADHl编码区长度为1134bp,编码378个氨基酸,由7个外显子和6个内含子构成,定位于Gm08染色体。GmASADH2编码区长度为1131bp,编码377个氨基酸,由7个外显子和6个内含子构成,定位于Gm05染色体。两个基因在氨基酸水平上的相似性达到了96.02%,在二级及三级结构上均有不同程度的差异。ASADH蛋白含有NADB—Rossmannsuper-family和Semialdhyde—dhCsuperfamily结构域。 相似文献
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为缩短传统大豆发酵制品后熟期,基于转氨反应这一主要风味形成途径,现从贵州各地采集风味良好的豆豉、腐乳等发酵样品,经稀释涂布平板法分离得到150株细菌。通过支链氨基酸转氨酶活力测定,从中筛选出WDH-8菌株具有最高酶活力,菌种鉴定后确定其为地衣芽孢杆菌,属安全益酵菌株,其支链氨基酸转氨酶活力达36.53U/mL。为便于生产应用,对该菌株进行固态菌剂培养基配方实验,以转氨酶活力为指标,培养基最佳配方为:黄豆粉25g、水料比1:1(V/m)、氯化钠添加量5%、葡萄糖添加量3%,其酶活力达到37.965U/mL。 相似文献