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四季豆幼苗中尿囊酸酰胺水解酶的一些特性
引用本文:徐志伟,周华新,黄维南.四季豆幼苗中尿囊酸酰胺水解酶的一些特性[J].植物生理与分子生物学学报,2004,30(4):460-468.
作者姓名:徐志伟  周华新  黄维南
作者单位:1. Department of Internal Medicine, University of Iowa, Iowa, IA 52242, USA
2. 福建省亚热带植物研究所,厦门,361006
摘    要:酰脲代谢在许多固氮豆科植物氮素代谢中起重要作用;尿囊酸的酰胺水解酶(EC3.5.3.9)分解尿囊酸成为脲基乙醇酸和CO2、NH3,脲基乙醇酸的酰胺水解酶进一步分解脲基乙醇酸产生乙醛酸和CO2、NH3.该文首次报告测定四季豆尿囊酸降解酶(分解尿囊酸的酶)的方法,酶反应基质需要盐酸苯肼存在.在四季豆干种子、幼苗根、茎和叶,均可测出尿囊酸降解酶活力.从四季豆幼苗分离出两个尿囊酸降解酶.一个分子量大于200 kD,另一个分子量为13.5 kD;小分子量的尿囊酸降解酶(没有脲基乙醇酸酰胺水解酶或脲酶活力)用于性质研究.酶反应产物分析表明,该酶是尿囊酸的酰胺水解酶.该酶反应的最适pH为8.5.Mn2 是该酶的金属辅助因子.Km为76μmol/L,Vmax为16.7 nKat/mg(=1 002 nmol min1mg1).乙醛酸和乙醇酸抑制该酶活力.赖氨酸残基和色氨酸残基是酶活力的必需基团;巯基和酪氨酸残基不是酶活力的必需基团.

关 键 词:尿囊酸酰胺水解酶  性质  四季豆

Some Properties of the Allantoate Amidohydrolase from French Bean Seedlings
Abstract.Some Properties of the Allantoate Amidohydrolase from French Bean Seedlings[J].Journal Of Plant Physiology and Molecular Biology,2004,30(4):460-468.
Authors:Abstract
Institution:Department of Internal Medicine, University of Iowa, IA 52242, USA. zhiwei-xu@uiowa.edu
Abstract:Allantoate degradation was demonstrated in the extracts of ungerminated seeds and roots, stems and leaves in germinated seedlings of French bean (Phaseolus vulgaris L.). Activity of allantoate-degrad- ing enzyme could only be measured when phenylhy- drazine was included in the assay mixture. Partial pu- rification of allantoate-degrading enzyme from seed- lings was performed and two fractions with allantoate- degrading enzyme activity were obtained. The molecu- lar mass of the first fraction was over 200 kD and that of the second one was 13.5 kD. The allantoate-degrad- ing enzyme with small molecular weight contained no activity of either ureidoglycolate-degrading enzyme or urease. From the stoichiometry of the reaction cata- lyzed by the allantoate-degrading enzyme with small molecular weight it followed that the enzyme was allantoate amidohydrolase (EC 3.5.3.9). The optimal pH for the allantoate amidohydrolase was 8.5. Mn2 ions were essential for enzymatic activity. Glyoxylate and glycolate strongly inhibited the enzyme activity. The lysine and tryptophan residues were essential to the enzymatic catalysis; thiol group and tyrosyl resi- dues were not involved in the enzyme catalysis.
Keywords:allantoate amidohydrolase  properties  French bean
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