Thermokinetic Study on the Reversible Competitive Inhibition of Bovine Liver Arginase

Introduction Arginase (EC 3.5.3.1) is a widespread and very im-portant enzyme in mammals, which specifically cata-lyzes the hydrolysis of L-arginine to urea and the non-protein amino acid L-ornithine, a key step in the urea cycle.1 Urea is the principal metabolite for disposal of nitrogen as a neutral and nontoxic waste product formed during amino acid metabolism in mammals. L-ornithine serves as a biosynthetic precursor to L-proline and the polyamines such as putrescine, sper-mine (in eucar…     

Microcalorimetric Studies on the Product Inhibition of Hydrolysis of L-arginine Catalyzed by Bovine Liver Arginase

A new thermokinetic reduced extent method for the product inhibition of single substrate enzyme-catalyzed reactions is proposed and compared with the traditional initial rate method in this paper. The arginase-catalyzed hydrolysis of L-arginine to L-ornithine and urea was studied at 37°C in 40 mM sodium barbiturate-HCl buffer solution (pH=9.4). Michaelis constant (K _m) for arginine and maximum velocity (V _m) of the reaction were determined by initial method and thermokinetic method. The activation of exogenous manganese to this reaction was also studied. The product inhibition constant (K _P), which cannot be obtained directly from the initial rate method, was determined by thermokinetic without adding L-ornithine to the reaction system. When the concentration of Mn²⁺ in cell is 0.1 mM, the enzyme gets its full activity. Incubation arginase with appropriate concentration of Mn²⁺resulted in increased Vmax and a higher sensitivity of the enzyme to product with no change in the K _m for arginine. We suggest that the exogenous manganese ions in solution have just recovered the activity of arginase, which was lost in dissolving and dilution, but no effect on the mechanism of the reaction. This revised version was published online in August 2006 with corrections to the Cover Date.     

国产732型阳离子交换树脂吸附L-精氨酸的特性

考察了溶液中氯化钠和氯化铵浓度、pH值、温度对732阳离子交换树脂吸附L－精氨酸的影响规律。结果表明：随着无机盐浓度的增大L－精氨酸的吸附率急剧降低，且盐浓度在大于1.0mol/L时几乎无法吸附；在低于等电点下，随着pH值的下降L－精氨酸的吸附率增大；适当升高温度，有助于提高L－精氨酸的吸附率。     

生产L-精氨酸的脯氨酸营养缺陷型菌株的选育

以谷氨酸棒杆菌（Corynebacterium glutamicum）BC001为出发菌株,经紫外单因子诱变、紫外与硫酸二乙酯复合诱变处理,获得一株脯氨酸营养缺陷型菌株BC3071584（D- Arg^r; Pro^-）,菌株的结构类似物抗性为6 g/L,在含葡萄糖质量浓度为40 g/L的培养基中摇瓶发酵96 h,L-精氨酸产量为5.76 g/L,相比出发菌株提高了10倍。     

Etch pit study of different crystallographic faces of L-arginine hydrobromide monohydrate (LAHBr) in alcohols

Chemical etchants based on simple alcohols were successfully applied for the first time to reveal dislocation sites on the polished {1 0 0}, {0 1 0}, {0 0 1} and {1 1 0} faces of L-arginine hydrobromide monohydrate. Fast dissolving etchants could produce etch pits only on the ‘F' faces but they have no effect on the ‘S' face. Selective behaviour of the etchants for revealing inclined dislocations and cooperating spirals has been demonstrated. Presence of growth spirals on {0 0 1} and {1 1 0} faces reveal that growth of these faces is governed by screw dislocation mechanism.     

钯掺杂聚精氨酸修饰电极同时测定5-羟基色氨酸和多巴胺

制备了钯掺杂聚L-精氨酸修饰玻碳电极(Pd-PA/GCE),研究了5-羟基色氨酸(5-HTP)和多巴胺(DA)在该修饰电极上的电化学行为,建立了同时测定5-HTP和DA的电化学新方法。在pH=2.0的磷酸缓冲溶液中,扫描速率为160mV/s时,DA在该电极上产生一对氧化还原峰,峰电位分别为0.515V和0.464V;5-HTP在该电极上产生一个氧化峰,峰电位为0.643V,两者的氧化峰电位差达128mV。在最优条件下,同时测定5-HTP和DA的线性范围分别为:9.00×10-7~1.00×10-5 mol/L、1.00×10-5~4.00×10-5 mol/L(5-HTP);7.00×10-7~1.00×10-5 mol/L、1.00×10-5~4.00×10-5 mol/L(DA)。检出限分别为7.0×10-7 mol/L和5.0×10-7 mol/L。方法可用于药剂中5-HTP和DA的测定。     

毛细管电泳-化学发光法用于L-精氨酸纯度分析

基于碱性介质中精氨酸对鲁米诺-铁氰化钾化学发光体系有增敏作用的事实,建立了毛细管电泳-化学发光法鉴定L-精氨酸纯度的新方法.优化发光条件为:缓冲溶液为2.5×10-3mol.L-1硼砂含2×10-3mol.L-1鲁米诺,氧化试剂为2×10-4mol.L-1铁氰化钾(用氢氧化钠调节pH值为13.3).在保证L-精氨酸与其产品中的杂质基线分离的情况下,得到L-精氨酸的线性范围为0.001 43~0.143 mol.L-1,检出限(S/N=3)为1.43×10-3mol.L-1.通过对来源不同的三种L-精氨酸标准样品进行分析,效果令人满意.     

靶向iNOS的雷公藤甲素氨基酸前药的合成

雷公藤甲素(TL)是从卫矛科雷公藤中提取的环氧二萜内酯,具有显著的抗炎和免疫抑制活性,但TL本身毒性较大、水溶性差、治疗窗窄,极大地限制其在临床上的应用.以炎症部位过度表达的诱导型一氧化氮合酶(iNOS)为靶点,在TL结构中引入iNOS底物及其类似物设计合成系列雷公藤甲素氨基酸前药,提高其水溶性和靶向性.雷公藤甲素氨基...     

A General Procedure for Synthesis of NG-Alkyl,and NG-Aryl-L-Arginines as Potential Nitric Oxide Synthase inhibitors

A general procedure for the synthesis of N^G-alkyl, and N^G-aryl-L -arginines with relatively high overall yield is reported. The key step involved the coupling of protected L -ornithine 4 with isothiourea 7 to give the fully protected N^G-aryl-L -arginine derivative 8 . Subsequent deprotection of 8 in acidic condition provided the final target compound 9 with an overall yield of more than 80%.     

羧酸型离子交换纤维吸附L-精氨酸

测定羧酸型离子交换纤维吸附L-精氨酸的动力学曲线和吸附等温线,详细考察温度、pH值、氯化铵和氯化钠浓度等因素对其吸附L-精氨酸的影响,结果表明,离子交换纤维吸附L-精氨酸20min后,基本上达到平衡,L-精氨酸在纤维上的吸附,可以用Langmuir方程来描述;温度对吸附影响很小,在实验pH范围内,随着pH升高吸附量增大,直到pH为9时达到最大;而当pH高于10后吸附量迅速下降．溶液中铵离子或钠离子浓度增大,L-精氨酸的吸附量迅速下降。