Variations in dietary protein but not in dietary fat plus cellulose or carbohydrate levels affect cysteine metabolism in rat isolated hepatocytes
Variations in dietary protein but not in dietary fat plus cellulose or carbohydrate levels affect cysteine metabolism in rat isolated hepatocytes
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DOI：
10.1093/jn/126.9.2179
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发表时间：
1996-09-01
影响因子：
4.2
通讯作者：
Stipanuk, MH
中科院分区：
文献类型：
--
作者：
Bella, DL;Kwon, YH;Stipanuk, MH
为了确定之前观察到的饮食蛋白质对肝脏半胱氨酸代谢的影响是由于饮食蛋白质的增加还是伴随的饮食碳水化合物的减少，进行了两个实验。在一项实验中，大鼠被喂以含有不同水平蛋白质的饮食，而不是脂肪+纤维素和恒定量碳水化合物的等卡路里混合物。在另一组中，大鼠被喂以含有恒定蛋白质但碳水化合物水平不同的饮食，而不是脂肪+纤维素的等卡路里混合物。饲喂2~3wk，分离肝细胞。当饲料中添加蛋白质时，肝脏半胱氨酸双加氧酶活性逐渐升高，半胱氨酸亚硫酸盐脱羧酶和γ-谷氨酰半胱氨酸合成酶活性逐渐降低。半胱氨酸二加氧酶、半胱氨酸亚磺酸脱羧酶和γ-谷氨酰半胱氨酸合成酶活性的变化分别与半胱氨酸分解代谢率、牛磺酸生成率和谷胱甘肽合成率的变化相一致。当改变碳水化合物、脂肪和纤维素的比例，而蛋白质水平保持不变时，酶活性或代谢物产生水平几乎或没有变化。参与半胱氨酸代谢的酶活性的调节主要是由于饮食蛋白质摄入量的变化，而不是与其他膳食常量营养素摄入量的相关变化。
To determine If previously observed effects of dietary protein on hepatic cysteine metabolism were due specifically to increases in dietary protein or to the accompanying decreases in dietary carbohydrate, two experiments were conducted. In one experiment, rats were fed diets that contained different levels of protein vs. an isocaloric mixture of fat + cellulose and a constant amount of carbohydrate. In the other, rats were fed diets that contained a constant amount of protein but different levels of carbohydrate vs. an isocaioric mixture of fat + cellulose. Diets were fed for 2-3 wk and hepatocytes were then isolated. Hepatic cysteine dioxygenase activity increased and cysteinesulfinate decarboxylase and gamma-glutamylcysteine synthetase activities decreased in a stepwise manner when protein was added to the diet at the expense of fat + cellulose. Changes in cysteine dioxygenase, cysteinesulfinate decarboxylase and gamma-glutamylcysteine synthetase activities were consistent with changes in rates of cysteine catabolism, taurine production and glutathione synthesis, respectively, by intact hepatocytes incubated with 0.2 mmol/L cysteine. When the carbohydrate to fat + cellulose ratio was varied, but the protein level was held constant, little or no change in enzyme activities or levels of metabolite production was observed. Regulation of the activities of enzymes involved in cysteine metabolism is predominantly due to changes in dietary protein intake and not to the associated changes in intake of other dietary macronutrients.