ESCHERICHIA-COLI MUTANTS DEFICIENT IN ASPARTATE AND AROMATIC AMINO-ACID AMINOTRANSFERASES
ESCHERICHIA-COLI MUTANTS DEFICIENT IN ASPARTATE AND AROMATIC AMINO-ACID AMINOTRANSFERASES
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DOI：
10.1128/jb.130.1.429-440.1977
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发表时间：
1977-01-01
影响因子：
3.2
通讯作者：
STEINBERG, RA
中科院分区：
文献类型：
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作者：
GELFAND, DH;STEINBERG, RA
描述了两个新的突变，它们一起基本上消除了E. K-12菌株中酪氨酸、苯丙氨酸和天冬氨酸从头生物合成所需的所有氨基转移酶活性。杆菌一个突变，命名为tyrB，位于. apprx。80分钟的E。大肠杆菌图谱和失活酪氨酸抑制酪氨酸/苯丙氨酸氨基转移酶。第二个突变，aspC，映射在. apprx。20分钟，并灭活对芳香族氨基酸也具有活性的不可抑制的天冬氨酸转氨酶。在缺乏支链氨基酸氨基转移酶的ilvE-菌株中，酪氨酸可抑制的氨基转移酶或天冬氨酸氨基转移酶的存在足以在不存在外源酪氨酸、苯丙氨酸或天冬氨酸的情况下生长;酪氨酸可抑制的酶在亮氨酸生物合成中也有活性。ilvE基因产物单独可以逆转苯丙氨酸需求。对携带这些氨基转移酶突变的组合的菌株的提取物的生物化学研究证实存在2种不同的酶，其对α-氨基转移酶具有重叠的特异性。酪氨酸、苯丙氨酸和天冬氨酸的酮酸类似物。这些酶可以通过电泳迁移率、使用各种底物的动力学参数和酪氨酸抑制性的差异来区分。在ilvE-tyrB- aspC-三重突变体的提取物中，对于α- tyrB- aspC-没有氨基转移酶活性。可以检测到酪氨酸、苯丙氨酸或天冬氨酸的酮酸。
Two new mutations are described which, together, eliminate essentially all the aminotransferase activity required for de novo biosynthesis of tyrosine, phenylalanine and aspartic acid in a K-12 strain of E. coli. One mutation, designated tyrB, lies at .apprx. 80 min on the E. coli map and inactivates the tyrosine-repressible tyrosine/phenylalanine aminotransferase. The 2nd mutation, aspC, maps at .apprx. 20 min and inactivates a nonrepressible aspartate aminotransferase that also has activity on the aromatic amino acids. In ilvE- strains, which lack the branched-chain amino acid aminotransferase, the presence of the tyrosine-repressible aminotransferase or the aspartate aminotransferase is sufficient for growth in the absence of exogenous tyrosine, phenylalanine or aspartate; the tyrosine-repressible enzyme is also active in leucine biosynthesis. The ilvE gene product alone can reverse a phenylalanine requirement. Biochemical studies on extracts of strains carrying combinations of these aminotransferase mutations confirm the existence of 2 distinct enzymes with overlapping specificities for the .alpha.-keto acid analogs of tyrosine, phenylalanine and aspartate. These enzymes can be distinguished by electrophoretic mobilities, by kinetic parameters using various substrates and by a difference in tyrosine repressibility. In extracts of an ilvE- tyrB- aspC- triple mutant, no aminotransferase activity for the .alpha.-keto acids of tyrosine, phenylalanine or aspartate could be detected.