Shin M, Mori Y, Kimura A, Fujita Y, Yoshida K, Sano K, Umezawa C
School of Pharmacy, Kobe Gakuin University, Japan.
Biochem Pharmacol. 1996 Jul 26;52(2):247-52. doi: 10.1016/0006-2952(96)00201-8.
Hepatocytes were isolated from rats fed a diet with or without 0.25% clofibrate, and NAD+ synthesis by the hepatocytes was determined using either [carboxyl-14C]nicotinic acid or [5-3H]tryptophan. NAD+ and total pyridine nucleotides synthesized from [14C]nicotinic acid by the clofibrate-treated cells were not significantly different from those synthesized by the control cells when expressed on the basis of nanomoles per hour per milligram of DNA. On the contrary, NAD+ synthesized from [3H]tryptophan was significantly higher in the clofibrate-treated cells (158% of the control cells) on the basis of nanomoles per hour per milligram of DNA. Clofibrate was inhibitory to tryptophan metabolism as a whole, affecting the glutarate pathway more (decreased to 37% of control) than the kynureninase flux (decreased to 64% of control). As a result, the quinolinate-NAD flux, estimated as the difference in the amounts of tryptophan metabolized by the two metabolic pathways, increased in the clofibrate-treated hepatocytes. The increase in quinolinate during the incubation was 8 times more in the clofibrate-treated cells than in the control cells, which confirmed alteration in the metabolic fluxes of tryptophan in the clofibrate-treated cells. Hepatic quinolinate phosphoribosyltransferase (EC 2.4.2.19) activity increased with dietary clofibrate and returned to the control level 1 week after removing clofibrate from the diet. Nicotinate phosphoribosyltransferase (EC 2.4.2.11) and NAD+ glycohydrolase (EC 3.2.2.5) activities remained unchanged with dietary clofibrate.
从喂食含或不含0.25%氯贝丁酯饮食的大鼠中分离肝细胞，使用[羧基-¹⁴C]烟酸或[5-³H]色氨酸测定肝细胞的NAD⁺合成。当以每小时每毫克DNA的纳摩尔数表示时，经氯贝丁酯处理的细胞由[¹⁴C]烟酸合成的NAD⁺和总吡啶核苷酸与对照细胞合成的无显著差异。相反，以每小时每毫克DNA的纳摩尔数计，经氯贝丁酯处理的细胞中由[³H]色氨酸合成的NAD⁺显著更高（为对照细胞的158%）。氯贝丁酯总体上抑制色氨酸代谢，对戊二酸途径的影响更大（降至对照的37%），比对犬尿氨酸酶通量的影响（降至对照的64%）更大。结果，通过两种代谢途径代谢的色氨酸量之差估算的喹啉酸-NAD通量在经氯贝丁酯处理的肝细胞中增加。孵育期间，经氯贝丁酯处理的细胞中喹啉酸的增加量比对照细胞高8倍，这证实了经氯贝丁酯处理的细胞中色氨酸代谢通量的改变。肝喹啉酸磷酸核糖基转移酶（EC 2.4.2.19）活性随饮食中的氯贝丁酯增加，在从饮食中去除氯贝丁酯1周后恢复到对照水平。烟酸磷酸核糖基转移酶（EC 2.4.2.11）和NAD⁺糖水解酶（EC 3.2.2.5）活性随饮食中的氯贝丁酯保持不变。
