Iyengar Vasuprada, Pullakhandam Raghu, Nair K Madhavan
Micronutrient Research Group, Biophysics Division, National Institute of Nutrition, Indian Council of Medical Research, Jamai Osmania, Ilyderabad 500 604, India.
Indian J Biochem Biophys. 2009 Aug;46(4):299-306.
Iron and zinc interact at the enterocyte during absorption, but the mechanism(s) remain elusive. The aim was, therefore, to understand the mechanism of interaction using kinetic analyses of iron and zinc uptake, individually and in combination under normal and altered cellular mineral concentrations in human intestinal Caco-2 cell line. Striking differences in kinetic parameters were observed between iron and zinc uptake. Iron uptake followed a two-component model, while zinc uptake followed a three-component model. Iron uptake had a Km of 3.6 microM and Vmax of 452 pmol/mg protein/min, while zinc uptake had a Km of 42 microM and Vmax of 3.09 pmol/mg protein/min. Zinc dose-dependently inhibited iron uptake through mixed-inhibition but iron marginally increased zinc uptake. Cellular zinc repletion doubled iron uptake and eliminated inhibition, but zinc depletion decreased iron uptake. Iron pre-treatment had no effect on zinc uptake. Based on these results, a two-transporter model of iron uptake, comprising the apical iron uptake transporter divalent metal ion transporter-1 (DMT-1) and an unknown putative transporter was derived. This model for DMT-1 was verified by immunoblotting. These results implied that cellular zinc status profoundly influenced iron uptake and its interactions with zinc during uptake. DMT-1 might not simultaneously transport iron and zinc, providing a mechanistic basis for observed interactions.
铁和锌在吸收过程中于肠细胞处相互作用，但其机制仍不清楚。因此，本研究旨在通过对人肠道Caco-2细胞系在正常及改变的细胞矿物质浓度下单独及联合摄取铁和锌的动力学分析，来了解其相互作用机制。观察到铁和锌摄取的动力学参数存在显著差异。铁摄取遵循双组分模型，而锌摄取遵循三组分模型。铁摄取的米氏常数（Km）为3.6微摩尔，最大反应速度（Vmax）为452皮摩尔/毫克蛋白质/分钟，而锌摄取的Km为42微摩尔，Vmax为3.09皮摩尔/毫克蛋白质/分钟。锌剂量依赖性地通过混合抑制作用抑制铁摄取，但铁对锌摄取的增加作用微弱。细胞内锌充足使铁摄取增加一倍并消除了抑制作用，但锌缺乏则降低铁摄取。铁预处理对锌摄取无影响。基于这些结果，推导了一个铁摄取的双转运体模型，该模型包括顶端铁摄取转运体二价金属离子转运体-1（DMT-1）和一个未知的假定转运体。通过免疫印迹法验证了该DMT-1模型。这些结果表明，细胞内锌状态深刻影响铁摄取及其在摄取过程中与锌的相互作用。DMT-1可能不会同时转运铁和锌，这为观察到的相互作用提供了机制基础。
