García-Campusano Florencia, Anaya Víctor-Hugo, Robledo-Arratia Luis, Quezada Héctor, Hernández Hugo, Riego Lina, González Alicia
Departamento de Genetica Molecular, Instituto de Fisiologia Celular, Universidad Nacional Autonoma de Mexico, Apartado Postal 70-242, Mexico City, D.F. 04510, Mexico.
Can J Microbiol. 2009 Apr;55(4):368-74. doi: 10.1139/w08-150.
In the yeast Saccharomyces cerevisiae, the paralogous genes ALT1 and ALT2 have been proposed to encode alanine aminotransferase isozymes. Although in other microorganisms this enzyme constitutes the main pathway for alanine biosynthesis, its role in S. cerevisiae had remained unclear. Results presented in this paper show that under respiratory conditions, Alt1p constitutes the sole pathway for alanine biosynthesis and catabolism, constituting the first example of an alanine aminotransferase that simultaneously carries out both functions. Conversely, under fermentative conditions, it plays a catabolic role and alanine is mainly synthesized through an alternative pathway. It can thus be concluded that ALT1 has functions in alanine biosynthesis and utilization or only alanine utilization under respiratory and fermentative conditions, respectively. ALT2 expression was repressed under all tested conditions, suggesting that Alt2p biosynthesis is strictly controlled and only allowed to express under peculiar physiological conditions.
在酿酒酵母中，同源基因ALT1和ALT2被认为编码丙氨酸转氨酶同工酶。尽管在其他微生物中，这种酶是丙氨酸生物合成的主要途径，但其在酿酒酵母中的作用仍不清楚。本文给出的结果表明，在呼吸条件下，Alt1p构成了丙氨酸生物合成和分解代谢的唯一途径，这是丙氨酸转氨酶同时执行这两种功能的首个例子。相反，在发酵条件下，它发挥分解代谢作用，丙氨酸主要通过另一条途径合成。因此可以得出结论，ALT1分别在呼吸和发酵条件下具有丙氨酸生物合成和利用功能或仅具有丙氨酸利用功能。在所有测试条件下，ALT2的表达均受到抑制，这表明Alt2p的生物合成受到严格控制，仅在特殊的生理条件下才允许表达。
