Department of Diabetes and Clinical Nutrition, Graduate School of Medicine, Kyoto University, Shogoin, Sakyo-ku, Kyoto 606-8507, Japan.
Biochem Biophys Res Commun. 2010 Feb 26;393(1):73-8. doi: 10.1016/j.bbrc.2010.01.081. Epub 2010 Jan 25.
SIR2 protein, an NAD-dependent deacetylase, is localized to nucleus and is involved in life span extension by calorie restriction in yeast. In mammals, among the seven SIR2 homologues (SIRT1-7), SIRT3, 4, and 5 are localized to mitochondria. As SIRT5 mRNA levels in liver are increased by fasting, the physiological role of SIRT5 was investigated in liver of SIRT5-overexpressing transgenic (SIRT5 Tg) mice. We identified carbamoyl phosphate synthetase 1 (CPS1), a key enzyme of the urea cycle that catalyzes condensation of ammonia with bicarbonate to form carbamoyl phosphate, as a target of SIRT5 by two-dimensional electrophoresis comparing mitochondrial proteins in livers of SIRT5 Tg and wild-type mice. CPS1 protein was more deacetylated and activated in liver of SIRT5 Tg mice than in wild-type. In addition, urea production was upregulated in hepatocytes of SIRT5 Tg mice. These results agree with those of a previous study using SIRT5 knockout (KO) mice. Because ammonia generated during fasting is toxic, SIRT5 protein might play a protective role by converting ammonia to non-toxic urea through deacetylation and activation of CPS1.
SIR2 蛋白是一种 NAD 依赖性去乙酰化酶，存在于细胞核内，通过限制热量摄入可延长酵母的寿命。在哺乳动物中，在 7 种 SIR2 同源物（SIRT1-7）中，SIRT3、4 和 5 定位于线粒体。由于禁食可增加肝脏中 SIRT5mRNA 的水平，因此在 SIRT5 过表达转基因（SIRT5Tg）小鼠的肝脏中研究了 SIRT5 的生理作用。我们通过比较 SIRT5Tg 和野生型小鼠肝脏中的线粒体蛋白，通过二维电泳鉴定出 CPS1（尿素循环的关键酶，催化氨与碳酸氢盐缩合形成氨甲酰磷酸）为 SIRT5 的靶标。CPS1 蛋白在 SIRT5Tg 小鼠的肝脏中比在野生型中去乙酰化和激活程度更高。此外，SIRT5Tg 小鼠的肝细胞中尿素的生成增加。这些结果与之前使用 SIRT5 敲除（KO）小鼠的研究结果一致。由于禁食期间产生的氨是有毒的，因此 SIRT5 蛋白可能通过去乙酰化和激活 CPS1 将氨转化为无毒的尿素来发挥保护作用。
