Colombo J P, Pfister U, Cervantes H
Department of Clinical Chemistry, Inselspital, University of Berne, Switzerland.
Biochem Biophys Res Commun. 1990 Nov 15;172(3):1239-45. doi: 10.1016/0006-291x(90)91582-d.
Urea cycle enzymes are subjected to regulation by dietary proteins. We have shown that this is also the case for N-acetylglutamate synthetase (EC 2.3.1.1.) (NAGS). Four different groups (n = 7) of male Wistar rats received either a low protein (8.7%) or a high (32% and 51%) protein diet and a control diet of 17% protein. The NAGS-activity in the liver, assayed after 15 days of feeding the different diets, increased from 25 +/- 7 (controls, 17% protein) to 31 +/- 5 (32% protein) and to 52 +/- 17 (51% protein) nmoles.min-1.g-1 wet weight. It decreased in the group with low protein diet (8.7%) to 5 +/- 3. The ratio of the arginine stimulated to the unstimulated enzyme activity remained constant over the range of protein intake. Similar changes were observed for carbamylphosphate synthetase, ornithine carbamyltransferase and arginase. As it is known for these enzymes adaptive mechanisms in relation to variations in dietary protein consumption also could be demonstrated for the enzyme NAGS.
尿素循环酶受膳食蛋白质的调节。我们已经表明，N-乙酰谷氨酸合成酶（EC 2.3.1.1.）（NAGS）也是如此。将四组不同的雄性Wistar大鼠（每组n = 7）分别给予低蛋白（8.7%）、高蛋白（32%和51%）饮食以及17%蛋白质的对照饮食。在给予不同饮食15天后测定肝脏中的NAGS活性，其活性从25±7（对照组，17%蛋白质）增加到31±5（32%蛋白质），再增加到52±17（51%蛋白质）纳摩尔·分钟⁻¹·克⁻¹湿重。在低蛋白饮食组（8.7%）中，其活性降至5±3。在蛋白质摄入范围内，精氨酸刺激的酶活性与未刺激的酶活性之比保持恒定。对于氨甲酰磷酸合成酶、鸟氨酸氨甲酰转移酶和精氨酸酶也观察到了类似的变化。正如已知这些酶一样，与膳食蛋白质消耗变化相关的适应性机制也可在NAGS酶中得到证实。
