| 摘要 |
A high affinity and extremely selective tryptophan transport system present in human monocyte-derived macrophages is disclosed. Human monocyte-derived macrophages include two distinct transporters, a high affinity (Km=290±160 nM) transporter that is highly specific for tryptophan and a low affinity (Km=27±4 muM) transporter that is less specific for tryptophan, consistent with the known system L. The tryptophan transport system is predominantly (86%) sodium-independent. The high-affinity system is very specific for tryptophan and shows no transport of any other essential amino acids in the tryptophan transport concentration range. This high-affinity system is expressed at very low levels in fresh monocytes, but undergoes a 10-30 fold induction during macrophage differentiation. This high affinity, tryptophan-selective transport system allows macrophages to take up tryptophan efficiently under conditions of very low substrate concentration, such as can occur at sites of inflammation.
|
