Selhub J, Powell G M, Rosenberg I H
Am J Physiol. 1984 May;246(5 Pt 1):G515-20. doi: 10.1152/ajpgi.1984.246.5.G515.
The mechanism of intestinal absorption of 5-methyltetrahydrofolate (5- CH3THF ) has been the topic of some controversy. In the present study, we have used enzymatically prepared 5- CH3THF to characterize transport by rat intestinal loops in vivo and everted jejunal sacs in vitro. Transport of 5- CH3THF is saturable (Km = 5.2 microM) and highly pH dependent, with the rate of maximal transport occurring at pH 5.8. Transport is competitively inhibited by folic acid (Ki = 4.2 microM) and methotrexate (Ki = 4.65 microM). Metabolic poisons and anaerobiosis greatly reduce 5- CH3THF transport. We conclude that 5- CH3THF transport in the rat intestine occurs by the same structure-specific mechanism responsible for the transport of unreduced folic acid and other monoglutamyl folates.
5-甲基四氢叶酸（5-CH3THF）的肠道吸收机制一直存在一些争议。在本研究中，我们使用酶法制备的5-CH3THF来表征其在大鼠体内肠袢和体外外翻空肠囊中的转运情况。5-CH3THF的转运具有饱和性（Km = 5.2微摩尔）且高度依赖pH值，最大转运速率出现在pH 5.8时。叶酸（Ki = 4.2微摩尔）和甲氨蝶呤（Ki = 4.65微摩尔）可竞争性抑制其转运。代谢毒物和无氧环境会大大降低5-CH3THF的转运。我们得出结论，大鼠肠道中5-CH3THF的转运是通过与未还原叶酸及其他单谷氨酸叶酸转运相同的结构特异性机制进行的。
