Goto R, Suzuki T, Tamemasa O
J Biochem. 1979 Aug;86(2):363-9. doi: 10.1093/oxfordjournals.jbchem.a132534.
In a previous paper, we reported that various D-amino acids were taken up several times more effectively than the corresponding L-isomers into several tumors tested in vivo. In order to investigate this further, the in vitro uptake of D-[14C]leucine by Ehrlich ascites tumor cells was investigated in comparison with that of L-[14C]leucine. The distribution ratio, the effects of amino acids and pH, and an approximately linear Lineweaver-Burk plot indicated that D-leucine was transported by an active transport system for L-leucine. Vmax and ku, the first-order rate constant for the unsaturable component, for the uptake of D- and L-leucines decreased with a fall in temperature. The activation energies for Vmax and ku were in the range of 5-10 and 18-21 kcal/mol, respectively. The values for L-leucine were greater than those for D-leucine. Km for D-leucine transport increased with decreasing temperature, whereas Km for L-leucine decreased. This difference suggests that the large alkyl chains of D- and L-leucines bind to different portions of a carrier protein.
在之前的一篇论文中，我们报道了在体内测试的几种肿瘤中，各种D - 氨基酸的摄取效率比相应的L - 异构体高几倍。为了进一步研究这一现象，我们将埃利希腹水瘤细胞对D - [¹⁴C]亮氨酸的体外摄取与L - [¹⁴C]亮氨酸的摄取进行了比较。分布比率、氨基酸和pH值的影响以及近似线性的Lineweaver - Burk图表明，D - 亮氨酸是通过L - 亮氨酸的主动转运系统进行转运的。D - 和L - 亮氨酸摄取的Vmax和ku（不饱和成分的一级速率常数）随温度降低而下降。Vmax和ku的活化能分别在5 - 10千卡/摩尔和18 - 21千卡/摩尔范围内。L - 亮氨酸的值大于D - 亮氨酸的值。D - 亮氨酸转运的Km随温度降低而增加，而L - 亮氨酸的Km则降低。这种差异表明，D - 和L - 亮氨酸的大烷基链与载体蛋白的不同部分结合。
