Saito K, Ohta Y, Nagamura Y, Sasaki E, Ishiguro I
Department of Biochemistry, School of Medicine, Fujita-Gakuen Health University, Aichi.
Biochem Int. 1990;20(1):71-80.
The relationship between L-tryptophan uptake and tryptophan 2,3-dioxygenase activity in hepatocytes was examined and compared with the change of hepatic L-leucine, L-phenylalanine, and L-tyrosine uptakes using isolated hepatocytes of rats in which the oxygenase was induced with L-tryptophan or hydrocortisone. In L-tryptophan- or hydrocortisone-treated rat hepatocytes, the rate of L-tryptophan uptake into hepatocytes via the saturable high-affinity transport component significantly increased but the hepatic uptake rate of L-leucine did not change at all. In hydrocortisone-treated rat hepatocytes, a little stimulated hepatic uptake of L-phenylalanine or L-tyrosine was observed. In the stimulated hepatic uptake of L-tryptophan via the high-affinity transport component, the Km value did not change but the Vmax value increased. Liver plasma membranes prepared from rats treated with L-tryptophan or hydrocortisone showed the same binding rate of L-tryptophan to the membranes as those from control rats. In addition, hepatic L-tryptophan uptake via the high-affinity transport component correlated well with hepatic tryptophan 2,3-dioxygenase activity (r = 0.787). The present results indicate that the uptake of L-tryptophan into hepatocytes via a transport system which works under physiological conditions is closely related to hepatic tryptophan 2,3-dioxygenase activity.
研究了肝细胞中L-色氨酸摄取与色氨酸2,3-双加氧酶活性之间的关系，并使用经L-色氨酸或氢化可的松诱导该加氧酶的大鼠分离肝细胞，将其与肝脏L-亮氨酸、L-苯丙氨酸和L-酪氨酸摄取的变化进行比较。在经L-色氨酸或氢化可的松处理的大鼠肝细胞中，通过可饱和的高亲和力转运成分进入肝细胞的L-色氨酸摄取速率显著增加，但L-亮氨酸的肝脏摄取速率完全没有变化。在经氢化可的松处理的大鼠肝细胞中，观察到L-苯丙氨酸或L-酪氨酸的肝脏摄取略有刺激。在通过高亲和力转运成分刺激的L-色氨酸肝脏摄取中，Km值没有变化，但Vmax值增加。从经L-色氨酸或氢化可的松处理的大鼠制备的肝细胞膜显示，L-色氨酸与膜的结合率与对照大鼠的相同。此外，通过高亲和力转运成分的肝脏L-色氨酸摄取与肝脏色氨酸2,3-双加氧酶活性密切相关（r = 0.787）。目前的结果表明，在生理条件下起作用的转运系统将L-色氨酸摄取到肝细胞中与肝脏色氨酸2,3-双加氧酶活性密切相关。
