Mutations Associated with Functional Disorder of Xanthine Oxidoreductase and Hereditary Xanthinuria in Humans

Xanthine oxidoreductase (XOR) catalyzes the conversion of hypoxanthine to xanthine and xanthine to uric acid with concomitant reduction of either NAD⁺ or O₂. The enzyme is a target of drugs to treat hyperuricemia, gout and reactive oxygen-related diseases. Human diseases associated with genetically determined dysfunction of XOR are termed xanthinuria, because of the excretion of xanthine in urine. Xanthinuria is classified into two subtypes, type I and type II. Type I xanthinuria involves XOR deficiency due to genetic defect of XOR, whereas type II xanthinuria involves dual deficiency of XOR and aldehyde oxidase (AO, a molybdoflavo enzyme similar to XOR) due to genetic defect in the molybdenum cofactor sulfurase. Molybdenum cofactor deficiency is associated with triple deficiency of XOR, AO and sulfite oxidase, due to defective synthesis of molybdopterin, which is a precursor of molybdenum cofactor for all three enzymes. The present review focuses on mutation or chemical modification studies of mammalian XOR, as well as on XOR mutations identified in humans, aimed at understanding the reaction mechanism of XOR and the relevance of mutated XORs as models to estimate the possible side effects of clinical application of XOR inhibitors.     

Syntheses of 1,2,4-triazolo[4,3-c]pteridines. Potential substrates for xanthine oxidase

A synthetic route for the preparation of 9-phenyl-1,2,4-triazolo[4,3-c]pteridines 8 is described. Their reactivities towards xanthine oxidase from Arthrobacter M-4 are determined and compared with the pteridine derivatives 6-phenylpteridin-4[3H]-thione 5, 6-phenyl-4-thiomethylpteridine 6, 4-hydrazino-6-phenylpteridine 7, 3-N-methyl-6-phenylpteridin-4[3H]-thione 19, 4-amino-6-phenylpteridine 22 and 1-N-methyl-6-phenylpteridin-4[1H]-one 24, in order to inspect a possible influence of pyrimidine ring substitution pattern on their interaction with the bacterial enzyme. It has been suggested that a planar structure of the pteridine moiety and the substituents could be an important factor that so far has been overlooked when considering the enzyme activity. Some literature data are also discussed in view of revision of structure assignment of the compounds 12, 14, and 17. This revised version was published online in August 2006 with corrections to the Cover Date.     

Antioxidative activities of bran extracts from twenty one pigmented rice cultivars

Ethanol–water (70:30, v/v) extracts from the bran of rice seeds from twenty one pigmented and one nonpigmented rice cultivars were evaluated for antioxidative activities using the following tests: inhibition of peroxidation of linoleic acid; inhibition of peroxidation of rabbit lipid erythrocyte membranes; reduction of potassium ferricyanide, and scavenging of superoxide anions and hydroxyl radicals. With some exceptions, extracts from the pigmented rice seeds had higher antioxidative activity than did the nonpigmented variety. The following pigmented cultivars had the highest antioxidative activities in all tests: Jumlalocal-1, Parnkhari 203, DZ78, LK1-3-6-12-1-1, and Elwee. A significant correlation was also noted between reducing power, inhibition of erythrocyte ghost membrane peroxidation, and superoxide anion and hydroxyl radical scavenging. The results suggest that: (a) ferricyanide reducing power might be a useful and simple index for large-scale evaluation of antioxidative potencies of natural products present in rice; (b) pigmented rice varieties with high antioxidative activities provide a source of antioxidants and a genetic resource to develop new health-promoting rice cultivars.     

Scavenger effect of a mango (Mangifera indica L.) food supplement’s active ingredient on free radicals produced by human polymorphonuclear cells and hypoxanthine–xanthine oxidase chemiluminescence systems

The in vitro antioxidant and free radical scavenging properties of a stem bark aqueous extract of mango tree (Mangifera indica L.), whose formulations are used in Cuba as food supplements under the brand name of Vimang^®, were studied. Luminol-enhanced chemiluminescence was used to elucidate the effect of this extract on the generation of reactive oxygen species in PMA- or zymosan-stimulated human polymorphonuclear leukocytes and on superoxide radicals generated in the hypoxanthine–xanthine oxidase reaction. Chemiluminescence was reduced in a dose-dependent manner at extract concentrations from 5 to 100 μg/ml, most probably by inhibiting the superoxide generation reaction. Part of this M. indica extract antioxidant activity could be ascribed to the presence of mangiferin as its main component.     

朝鲜蓟叶提取物的体外抗氧化作用

对朝鲜蓟叶提取物(ALE)进行体外抗氧化实验,评价其抗氧化功能。采用4种不同的体外抗氧化评价体系对ALE进行抗氧化功能的评价,结果以IC50来表示。ALE在4种系统中表现出不同的抗氧化能力。其中以NH2OH-Xan-XOD系统的IC50值最低,为16.5μg/mL,二酪氨酸/酪氨酸系统的IC50值最高,为310μg/mL。ALE具有抗氧化作用,且存在剂量依赖效应。     

嗜黏蛋白阿克曼氏菌对高尿酸血症小鼠血清尿酸及组织炎症的影响及机制

目的：研究活的和巴氏杀菌处理的嗜黏蛋白阿克曼氏菌（Akkermansia muciniphila）对高尿酸血症小鼠血清尿酸水平及组织炎症的影响和潜在机制。方法：使用氧嗪酸钾和次黄嘌呤联合含20%（以体系质量计）酵母膏的饲料对ICR小鼠进行为期3周的高尿酸血症造模,同时分别灌胃活的和巴氏杀菌处理的嗜黏蛋白阿克曼氏菌作为处理组,采集小鼠血液和组织样品,测定小鼠血清尿酸浓度以及肝脏黄嘌呤氧化酶活力,并通过苏木精-伊红染色法进行小鼠肾和肠道病理分析。结果：不同形式的嗜黏蛋白阿克曼氏菌均能一定程度地降低小鼠血清尿酸浓度。肝脏黄嘌呤氧化酶活力检测以及蛋白印迹分析结果表明两种形式的嗜黏蛋白阿克曼氏菌能下调该酶活性及蛋白表达,从而减少肝脏尿酸的生成。肾和肠道组织病理分析结果表明模型组小鼠肾脏和肠道均有损伤,包括肾小球萎缩、肾间质炎性细胞浸润以及肠绒毛变短,嗜黏蛋白阿克曼氏菌处理能减轻这些症状。嗜黏蛋白阿克曼氏菌干预还能下调肾脏及肠道Toll样受体4和Caspase 1水平,从而抑制白细胞介素-1β表达,有效缓解小鼠脏器中的炎症反应。结论：嗜黏蛋白阿克曼氏菌能用于改善小鼠高尿酸血症,并且巴氏杀菌处理后的...     

黄嘌呤和谷氨酰胺对枯草芽孢杆菌XGL产腺苷的影响

该研究以枯草芽孢杆菌（Bacillus subtilis）XGL为出发菌株,探究黄嘌呤和谷氨酰胺添加量及添加方式对其产腺苷的影响。结果表明,底物中添加100 mg/L黄嘌呤并在发酵16 h后持续向发酵液中流加3 g/L的黄嘌呤溶液200 mL可使腺苷产量达到34.4 g/L,相比于不流加黄嘌呤时腺苷产量（11.2 g/L）提高207%。在此基础上,再向底物中添加6 g/L谷氨酰胺,发酵32 h之后持续向发酵液中流加6 g/L的谷氨酰胺,腺苷产量达到45.8 g/L,相比于不添加谷氨酰胺腺苷产量（34.4 g/L）提高33%。因此,在B. subtilis XGL发酵过程中,可以通过底物添加和流加补料的发酵方式加入一定量的黄嘌呤和谷氨酰胺以提高腺苷产量。     

鲣鱼蛋白肽谱效关系研究

采用鲣鱼为原料,以蛋白质回收率为指标,酶解制备不同工艺条件的样品。通过测定其黄嘌呤氧化酶(XOD)抑制活性、ORAC值、分子质量分布图谱和总氨基酸含量,构建鲣鱼蛋白肽体外化学活性与其分子质量分布图谱、总氨基酸含量图谱之间的谱效关系。结合超高效液相-质谱联用(LC-MS/MS)方法研究其降尿酸肽和抗氧化肽的分布。研究表明,鲣鱼蛋白肽的XOD抑制活性与其ORAC值具有显著的相关性。由多肽分子质量<1ku所占含量的分布区段和脂肪族氨基酸的含量可初步预测鲣鱼蛋白肽的化学活性。质谱分析表明,纯化组分的质谱基峰图在不同时间段的信号强度与鲣鱼蛋白肽的降尿酸活性和抗氧化活性具有明显的相关性。     

Scavenging effect of tea catechins and their epimers on superoxide anion radicals generated by a hypoxanthine and xanthine oxidase system

Catechins are a major group of polyphenolic compounds contained in abundance in green tea. Using electron spin resonance spectroscopy along with a spin‐trapping agent, the scavenging effect of tea catechins and their corresponding epimers against superoxide anion radicals generated by a hypoxanthine and xanthine oxidase reaction system was evaluated. The presence of 3′,4′,5′‐trihydroxyl groups attached to the B‐ring of the flavan skeleton of tea catechins elevated their radical‐scavenging efficiency in comparison to those with 3′,4′‐dihydroxyl groups. There were no significant differences between the four dominant tea catechins and their corresponding epimers with regard to radical‐scavenging ability. Under the different spin‐trapping agent concentrations, the sigmoid curves of reducing spin‐trapping adducts produced by tea catechins were shifted leftward, suggesting that a likely possible action of tea catechins is to scavenge superoxide anion radicals directly, not to inhibit the function of xanthine oxidase. Although caffeine is also known as a major ingredient of tea, its superoxide anion radical‐scavenging effect was much weaker than that of the catechin family. It is concluded that tea catechins and their epimers serve as powerful antioxidants for directly eliminating superoxide anion radicals, and may be useful in the prevention of diseases relating to in vivo oxidative stress. © 2000 Society of Chemical Industry     

酿酒酵母和大肠杆菌鸟嘌呤脱氨酶基因的克隆、原核表达及活性测定

与植物体内合成路径不同,微生物体内合成咖啡碱存在一条以黄嘌呤为底物,利用鸟嘌呤脱氨酶催化鸟嘌呤生成黄嘌呤有效合成咖啡碱的新途径。为克隆鸟嘌呤脱氨酶的基因,构建可高效合成黄嘌呤的原核表达载体并对外源蛋白活性进行检测,分别以酿酒酵母和大肠杆菌为研究材料,根据GenBank中酿酒酵母和大肠杆菌中鸟嘌呤脱氨酶基因gud1和egud序列设计引物,聚合酶链式反应特异扩增其基因片段,将目的基因连接至pMAL-c5X载体,转入大肠杆菌BL21（DE3）中诱导蛋白表达,并用高效液相色谱法鉴定其目的蛋白的催化活性。结果表明重组载体pMAL-gud1、pMAL-egud均可用来合成黄嘌呤,且GUD1比EGUD合成黄嘌呤的效率更高。研究结果将进一步丰富黑茶加工技术理论,同时为体外构建高效咖啡碱生物工程菌提供理论支持。