Said H M, Hoefs J, Mohammadkhani R, Horne D W
Veterans Administration Medical Center, Long Beach, California.
Gastroenterology. 1992 Jun;102(6):2120-5. doi: 10.1016/0016-5085(92)90341-u.
The characteristics of biotin transport into human liver were examined using purified liver basolateral membrane vesicle (BLMV) preparations. Biotin uptake by BLMVs was mostly due to transport of the vitamin into the inside of vesicles. In the presence of an Na+ gradient (out greater than in), biotin transport with time was significantly higher than that in the presence of a K+ gradient and showed transient accumulation (overshoot). High concentrations of unlabeled biotin and related compounds caused significant cis inhibition in biotin transport in the presence of an Na+ (but not a K+) gradient. Transport of biotin as a function of concentration in the presence of an Na+ gradient included a saturable component, while it was lower and linear in the presence of a K+ gradient. Apparent Km and Vmax of the saturable Na+ gradient-dependent component were 1.22 mumol/L and 4.76 pmol.mg protein-1 x 10 s-1, respectively. Induction of a negative or positive intravascular potential using valinomycin-K diffusion methodology did not affect biotin transport into BLMVs. Also, neither the anion-exchange inhibitor 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid nor 4-acetamido-4-isothiocyanostilbene-2,2'-disulfonic acid caused significant inhibition in biotin transport. These results indicate that biotin transport into human liver occurs via a specialized, carrier-mediated transport system. This system is Na(+)-gradient dependent and transports the vitamin via an electroneutral process.
利用纯化的肝基底外侧膜囊泡（BLMV）制剂研究了生物素转运至人肝脏的特性。BLMV对生物素的摄取主要是由于该维生素转运至囊泡内部。在存在Na⁺梯度（胞外大于胞内）的情况下，生物素随时间的转运显著高于存在K⁺梯度时的转运，并呈现瞬时积累（过冲）。高浓度的未标记生物素及相关化合物在存在Na⁺（而非K⁺）梯度时对生物素转运产生显著的顺式抑制。在存在Na⁺梯度时，生物素转运作为浓度的函数包含一个可饱和成分，而在存在K⁺梯度时其转运较低且呈线性。可饱和的Na⁺梯度依赖性成分的表观Km和Vmax分别为1.22 μmol/L和4.76 pmol·mg蛋白⁻¹×10 s⁻¹。使用缬氨霉素-K扩散方法诱导血管内负电位或正电位并不影响生物素转运至BLMV。此外，阴离子交换抑制剂4,4'-二异硫氰酸根合芪-2,2'-二磺酸和4-乙酰氨基-4-异硫氰酸根合芪-2,2'-二磺酸均未对生物素转运产生显著抑制。这些结果表明，生物素转运至人肝脏是通过一种特殊的、载体介导的转运系统进行的。该系统依赖Na⁺梯度，并通过电中性过程转运该维生素。
