Sacchi V F, Perego C, Magagnin S
Istituto di Fisiologia Generale e di Chimica Biologica, Facoltà di Farmacia, Milano, Italy.
J Exp Biol. 1995 Apr;198(Pt 4):961-6. doi: 10.1242/jeb.198.4.961.
The injection of poly(A)+ mRNA prepared from Philosamia cynthia midgut caused time- and dose-dependent increases of leucine transport in Xenopus laevis oocytes, with an increase in leucine uptake 1.5-3 times that of oocytes injected with water. When the NaCl concentration was reduced from 100 to 5 mmol l-1, the difference between mRNA- and water-injected oocytes was greater and a fourfold increase of L-leucine uptake was measured. D-Leucine (10 mmol l-1) completely inhibited the induced uptake of 0.1 mmol l-1 L-leucine. The newly expressed component of L-leucine uptake increased at alkaline pH and was abolished by incubation for 15 min with 15 mmol l-1 phenylglyoxal. The mean Km values, calculated using Na+ activation curves of leucine uptake, were 23.3 +/- 6.1 mmol l-1 in water-injected oocytes and 0.4 +/- 0.2 mmol l-1 for the newly expressed component of leucine uptake in mRNA-injected oocytes. On the basis of these results, we conclude that the increase of L-leucine uptake in mRNA-injected oocytes was due to the expression of a new transport system, which differs from the endogenous ones and shares many features with that found previously in Philosamia cynthia midgut.
注射从蓖麻蚕中肠制备的聚腺苷酸加尾信使核糖核酸（poly(A)+ mRNA），可使非洲爪蟾卵母细胞中的亮氨酸转运呈时间和剂量依赖性增加，亮氨酸摄取量比注射水的卵母细胞增加1.5至3倍。当氯化钠浓度从100毫摩尔/升降至5毫摩尔/升时，注射信使核糖核酸和注射水的卵母细胞之间的差异更大，L-亮氨酸摄取量增加了四倍。D-亮氨酸（10毫摩尔/升）完全抑制了0.1毫摩尔/升L-亮氨酸的诱导摄取。新表达的L-亮氨酸摄取成分在碱性pH值下增加，并在与15毫摩尔/升苯乙二醛孵育15分钟后消失。根据亮氨酸摄取的钠离子激活曲线计算，注射水的卵母细胞的平均米氏常数（Km值）为23.3±6.1毫摩尔/升，注射信使核糖核酸的卵母细胞中新表达的亮氨酸摄取成分的Km值为0.4±0.2毫摩尔/升。基于这些结果，我们得出结论，注射信使核糖核酸的卵母细胞中L-亮氨酸摄取的增加是由于一种新的转运系统的表达，该系统不同于内源性转运系统，并且与先前在蓖麻蚕中肠中发现的转运系统有许多共同特征。
