Hayase K, Yokogoshi H, Yoshida A
J Nutr. 1980 Jul;110(7):1327-37. doi: 10.1093/jn/110.7.1327.
A mechanism of regulation in urea biosynthesis under conditions of varying dietary protein quality was investigated in rats adapted to 10% protein diets. A reverse correlation was observed between activities of urea cycle enzymes and urinary excretion of urea under these conditions. The concentrations of several non-essential amino acids in livers of rats fed a 10% gluten diet significantly increased as compared with those of rats fed a 10% whole egg protein diet without change in ornithine concentration. The contents of threonine, serine and ornithine in livers of rats fed a methionine-free diet were higher than those of rats fed a basal diet. The capacity of urea synthesis in vivo of rats fed gluten or a methionine-free amino acid mixture was the same as that of rats fed whole egg protein or basal amino acid mixture. The results suggest that under conditions of varying dietary protein quality, the liver level of free amino acids may regulate mainly the rate of urea synthesis without changes in activities of urea cycle enzymes and that the concentrations of ornithine in addition to free amino acids in liver may play an important role in an increase of urea synthesis in the methionine-deficiency.
在适应10%蛋白质饮食的大鼠中，研究了不同膳食蛋白质质量条件下尿素生物合成的调节机制。在这些条件下，观察到尿素循环酶活性与尿素尿排泄之间呈负相关。与喂食10%全蛋蛋白饮食的大鼠相比，喂食10%麸质饮食的大鼠肝脏中几种非必需氨基酸的浓度显著增加，而鸟氨酸浓度没有变化。喂食无蛋氨酸饮食的大鼠肝脏中苏氨酸、丝氨酸和鸟氨酸的含量高于喂食基础饮食的大鼠。喂食麸质或无蛋氨酸氨基酸混合物的大鼠体内尿素合成能力与喂食全蛋蛋白或基础氨基酸混合物的大鼠相同。结果表明，在不同膳食蛋白质质量条件下，肝脏游离氨基酸水平可能主要调节尿素合成速率，而尿素循环酶活性不变，并且除肝脏游离氨基酸外，鸟氨酸浓度可能在蛋氨酸缺乏时尿素合成增加中起重要作用。
