Pedraza Raúl Osvaldo, Ramírez-Mata Alberto, Xiqui Ma Luisa, Baca Beatriz Eugenia
Centro de Investigaciones Microbiológicas, Instituto de Ciencias, Universidad Autónoma de Puebla, Apdo. Postal 1622. C.P. 72,000, Puebla Pue, Mexico.
FEMS Microbiol Lett. 2004 Apr 1;233(1):15-21. doi: 10.1016/j.femsle.2004.01.047.
In this work, we report the detection of aromatic amino acid aminotransferase (AAT) activity from cell-free crude extracts of nine strains of N(2)-fixing bacteria from three genera. Using tyrosine as substrate, AAT activity ranged in specific activity from 0.084 to 0.404 micromol min(-1)mg(-1). When analyzed under non-denaturating PAGE conditions; and using tryptophan, phenylalanine, tyrosine, and histidine as substrates Pseudomonas stutzeri A15 showed three isoforms with molecular mass of 46, 68 and 86 kDa, respectively; Azospirillum strains displayed two isoforms which molecular mass ranged from 44 to 66 kDa and Gluconacetobacter strains revealed one enzyme, which molecular mass was estimated to be much more higher than those of Azospirillum and P. stutzeri strains. After SDS-PAGE, some AAT activity was lost, indicating a differential stability of proteins. All the strains tested produced IAA, especially with tryptophan as precursor. Azospirillum strains produced the highest concentrations of IAA (16.5-38 microg IAA/mg protein), whereas Gluconacetobacter and P. stutzeri strains produced lower concentrations of IAA ranging from 1 to 2.9 microg/mg protein in culture medium supplemented with tryptophan. The IAA production may enable bacteria promote a growth-promoting effect in plants, in addition to their nitrogen fixing ability.
在本研究中，我们报告了从三个属的9株固氮细菌的无细胞粗提物中检测到芳香族氨基酸转氨酶（AAT）活性。以酪氨酸为底物时，AAT的比活性范围为0.084至0.404微摩尔·分钟⁻¹·毫克⁻¹。在非变性聚丙烯酰胺凝胶电泳（PAGE）条件下进行分析时，以色氨酸、苯丙氨酸、酪氨酸和组氨酸为底物，斯氏假单胞菌A15显示出三种分别具有46 kDa、68 kDa和86 kDa分子量的同工型；固氮螺菌属菌株显示出两种分子量范围为44至66 kDa的同工型，而葡糖醋杆菌属菌株显示出一种酶，其分子量估计比固氮螺菌属和斯氏假单胞菌属菌株的分子量高得多。十二烷基硫酸钠-聚丙烯酰胺凝胶电泳（SDS-PAGE）后，一些AAT活性丧失，表明蛋白质的稳定性存在差异。所有测试菌株均产生吲哚-3-乙酸（IAA），尤其是以色氨酸为前体时。固氮螺菌属菌株产生的IAA浓度最高（16.5 - 38微克IAA/毫克蛋白质），而在添加色氨酸的培养基中，葡糖醋杆菌属和斯氏假单胞菌属菌株产生的IAA浓度较低，范围为1至2.9微克/毫克蛋白质。除了固氮能力外，IAA的产生可能使细菌对植物产生促生长作用。
