Rindi G
Acta Vitaminol Enzymol. 1984;6(1):47-55.
In different animal species, including man, thiamin is absorbed in vivo from the small intestine by means of two mechanism: at low intraluminal concentrations (less than 1.5 microM), absorption shows a saturation kinetics; at higher concentrations, passive transport (diffusion) takes place. The absorption is maximal in the duodenum, its rate decreasing caudally along the small intestine. In vitro at low concentrations, the transcellular transport system of thiamin shows the following general features: it takes place against a chemical concentration gradient, is easily saturable (Km = 0.16-0.63 microM; Vmax = 5.2 mumol X g-1 X h-1), is blocked by cellular metabolic inhibitors, anoxia, low temperature and thiamin structural analogues. It is Na+-dependent and operates mainly from mucosa to serosa. In contrast, distinctive features of the thiamin transfer are the following: entry in the enterocyte in the free form (sodium-independent); pyrophosphorylation by means of a cytoplasm thiamin-pyrophosphokinase; the dephosphorylation of thiamin-pyrophosphate by means of particulate intracellular phosphatases; the cellular exit mainly in the free form, through the action of the controluminal Na-K activated ATPase. A working scheme for thiamin intestinal transport is proposed and discussed.
在包括人类在内的不同动物物种中，硫胺素在体内通过两种机制从小肠吸收：在肠腔内浓度较低（低于1.5微摩尔）时，吸收呈现饱和动力学；在较高浓度时，发生被动转运（扩散）。十二指肠的吸收最大，其速率沿小肠向尾部降低。在体外低浓度时，硫胺素的跨细胞转运系统具有以下一般特征：它逆化学浓度梯度进行，容易饱和（Km = 0.16 - 0.63微摩尔；Vmax = 5.2微摩尔×克-1×小时-1），被细胞代谢抑制剂、缺氧、低温和硫胺素结构类似物阻断。它依赖钠离子，主要从黏膜向浆膜运作。相比之下，硫胺素转运的独特特征如下：以游离形式（不依赖钠）进入肠细胞；通过细胞质硫胺素焦磷酸激酶进行焦磷酸化；通过颗粒状细胞内磷酸酶使硫胺素焦磷酸去磷酸化；细胞主要以游离形式通过腔面膜钠钾激活的ATP酶作用排出。提出并讨论了硫胺素肠道转运的工作方案。
