Urrestarazu A, Vissers S, Iraqui I, Grenson M
Laboratoire de Physiologie Cellulaire et de Génétique des Levures, Université Libre de Bruxelles, Belgium.
Mol Gen Genet. 1998 Jan;257(2):230-7. doi: 10.1007/s004380050643.
This paper reports the first isolation of Saccharomyces cerevisiae mutants lacking aromatic aminotransferase I activity (aro8), and of aro8 and aro9 double mutants which are auxotrophic for both phenylalanine and tyrosine, because the second mutation, aro9 affects aromatic aminotransferase II. Neither of the single mutants displays any nutritional requirement on minimal ammonia medium. In vitro, aromatic aminotransferase I is active not only with the aromatic amino acids, but also with methionine, alpha-aminoadipate, and leucine when phenylpyruvate is the amino acceptor, and in the reverse reactions with their oxo-acid analogues and phenylalanine as the amino donor. Its contribution amounts to half of the glutamate:2-oxoadipate activity detected in cell-free extracts and the enzyme might be identical to one of the two known alpha-aminoadipate aminotransferases. Aromatic aminotransferase I has properties of a general aminotransferase which, like several aminotransferases of Escherichia coli, may be able to play a role in several otherwise unrelated metabolic pathways. Aromatic aminotransferase II also has a broader substrate specificity than initially described. In particular, it is responsible for all the measured kynurenine aminotransferase activity. Mutants lacking this activity grow very slowly on kynurenine medium.
本文报道了首次分离出缺乏芳香族氨基转移酶I活性（aro8）的酿酒酵母突变体，以及aro8和aro9双突变体，这两种双突变体对苯丙氨酸和酪氨酸均为营养缺陷型，因为第二个突变aro9影响芳香族氨基转移酶II。这两种单突变体在基本氨培养基上均未表现出任何营养需求。在体外，当苯丙酮酸作为氨基受体时，芳香族氨基转移酶I不仅对芳香族氨基酸有活性，而且对蛋氨酸、α-氨基己二酸和亮氨酸也有活性；在以它们的氧代酸类似物和苯丙氨酸作为氨基供体的逆反应中也有活性。其贡献量占无细胞提取物中检测到的谷氨酸：2-氧代己二酸活性的一半，该酶可能与两种已知的α-氨基己二酸氨基转移酶之一相同。芳香族氨基转移酶I具有一般氨基转移酶的特性，与大肠杆菌的几种氨基转移酶一样，可能能够在几种原本不相关的代谢途径中发挥作用。芳香族氨基转移酶II也具有比最初描述的更广泛的底物特异性。特别是，它负责所有测定的犬尿氨酸氨基转移酶活性。缺乏这种活性的突变体在犬尿氨酸培养基上生长非常缓慢。
