Jara J R, Martinez-Liarte J H, Solano F, Peñafiel R
Dpto. Bioquimica y Biologia Molecular, Facultad de Medicina, Universidad de Murcia, Spain.
J Cell Sci. 1990 Nov;97 ( Pt 3):479-85. doi: 10.1242/jcs.97.3.479.
The uptake of L-Tyr by B16/F10 malignant melanocytes in culture has been studied. These melanoma cells can either be depleted of amino acids by 1 h preincubation in Hanks' isotonic medium or preloaded with a specific amino acid by 1 h preincubation in the same solution containing 2 mM of the amino acid to be preloaded. By means of these pretreatments, it is shown that the rate of L-Tyr uptake is greatly dependent on the content of other amino acids inside the cells. The L-Tyr uptake is higher in cells preloaded with amino acids transported by the L and ASC systems than in cells depleted of amino acids or preloaded with amino acids transported by the A system. It is concluded that L-Tyr is mainly taken up by an exchange mechanism with other amino acids mediated by the L1 system, although the ASC system can also participate in the process. In agreement with that, the homo-exchange performed by cells preloaded with unlabelled L-Tyr is more efficient than any other hetero-exchange, although L-Dopa, the product of tyrosine hydroxylation in melanin synthesis, is almost as efficient as L-Tyr. Apart from aromatic amino acids, melanoma cells preloaded with L-Met and L-His also yield a high initial rate of L-Tyr uptake. The results herein suggest that melanoma cells do not have transport systems specific for L-Tyr, even if this amino acid is needed to carry out the differential pathway of this type of cells, melanosynthesis.
已对培养的B16/F10恶性黑色素细胞摄取L-酪氨酸的情况进行了研究。这些黑色素瘤细胞既可以通过在汉克斯等渗培养基中预孵育1小时来耗尽氨基酸，也可以通过在含有2 mM待预加载氨基酸的相同溶液中预孵育1小时来预加载特定氨基酸。通过这些预处理表明，L-酪氨酸的摄取速率在很大程度上取决于细胞内其他氨基酸的含量。与耗尽氨基酸的细胞或预加载由A系统转运的氨基酸的细胞相比，预加载由L和ASC系统转运的氨基酸的细胞对L-酪氨酸的摄取更高。得出的结论是，L-酪氨酸主要通过由L1系统介导的与其他氨基酸的交换机制摄取，尽管ASC系统也可以参与该过程。与此一致的是，预加载未标记L-酪氨酸的细胞进行的同型交换比任何其他异型交换更有效，尽管黑色素合成中酪氨酸羟基化的产物L-多巴几乎与L-酪氨酸一样有效。除芳香族氨基酸外，预加载L-蛋氨酸和L-组氨酸的黑色素瘤细胞对L-酪氨酸的摄取也具有较高的初始速率。本文的结果表明，黑色素瘤细胞没有对L-酪氨酸特异的转运系统，即使这种氨基酸是进行这类细胞的特殊途径——黑色素合成所必需的。
