Briggs S, Freedland R A
J Nutr. 1977 Apr;107(4):561-6. doi: 10.1093/jn/107.4.561.
Urea cycle enzymes of rats were altered by feeding protein-free 15% casein, or 70% casein diets. Cells isolated from the livers of these rats were incubated with 10 mM ammonia and varying levels of ornithine (2 or 10 mM) and lactate (0-10 mM). Conditions providing the greatest rate of urea synthesis depended on the diet consumed and on whether rats were fed or starved 24 hours before cell isolation. Maximum rates of urea synthesis, though not different for the fed and starved groups, increased with the protein content of the diet and were equal to the maximum theoretical rates, as determined by argininosuccinate synthetase activity. This indicates that with optimal conditions, the activity of argininosuccinate synthetase is the rate-limiting factor in the synthesis of urea in isolated hepatocytes.
通过给大鼠喂食无蛋白、15%酪蛋白或70%酪蛋白饮食，可改变其尿素循环酶。从这些大鼠肝脏分离出的细胞与10 mM氨以及不同水平的鸟氨酸（2或10 mM）和乳酸（0 - 10 mM）一起孵育。提供最大尿素合成速率的条件取决于所消耗的饮食以及细胞分离前大鼠是喂食还是饥饿24小时。尿素合成的最大速率，尽管喂食组和饥饿组没有差异，但随饮食中蛋白质含量增加，且与精氨琥珀酸合成酶活性所确定的最大理论速率相等。这表明在最佳条件下，精氨琥珀酸合成酶的活性是分离的肝细胞中尿素合成的限速因素。
