Cheeseman C I, Johnston G
Can J Physiol Pharmacol. 1982 Sep;60(9):1177-84. doi: 10.1139/y82-171.
The uptake of the peptide glycyl-L-leucine across the brush border of the rat small intestinal enterocyte was studied using everted rings. The transfer of leucine from the dipeptide into the enterocyte was greater than the glycine uptake from glycyl-L-leucine. This additional component for leucine transport was found to be abolished by the removal of sodium, by the presence of 10 mM L-alanine beta-naphthylamide, and by excess free leucine. In contrast, the uptake of glycine from glycyl-L-leucine was not sodium-dependent and was not reduced by the presence of excess free leucine. The presence of harmaline over a concentration range up to 10 mM inhibited some of the peptide-bound leucine and glycine uptake. Transport of leucine from glycyl-L-leucine in the presence of 20 mM free leucine was competitively inhibited by glycyl-L-proline, although not completely. It is concluded that, in the rat, the sodium-sensitive component of amino acid uptake from the dipeptide represents free amino acid liberated by superficial hydrolysis, while the transport of the intact peptide is not sodium dependent. In addition, it appears that there are at least two routes of entry for the intact dipeptide glycyl-L-leucine, only one of which is shared with glycyl-L-proline.
利用外翻肠段研究了大鼠小肠肠上皮细胞刷状缘对肽甘氨酰 - L - 亮氨酸的摄取。从二肽中转运至肠上皮细胞的亮氨酸量大于从甘氨酰 - L - 亮氨酸中摄取的甘氨酸量。发现这种额外的亮氨酸转运成分可被去除钠离子、存在10 mM L - 丙氨酸β - 萘酰胺以及过量游离亮氨酸所消除。相比之下，从甘氨酰 - L - 亮氨酸中摄取甘氨酸不依赖于钠离子，且不会因过量游离亮氨酸的存在而减少。在浓度高达10 mM的范围内，harmaline的存在会抑制部分肽结合的亮氨酸和甘氨酸摄取。在存在20 mM游离亮氨酸的情况下，甘氨酰 - L - 脯氨酸会竞争性抑制甘氨酰 - L - 亮氨酸中亮氨酸的转运，尽管抑制并不完全。得出的结论是，在大鼠中，从二肽摄取氨基酸的钠敏感成分代表了由表面水解释放的游离氨基酸，而完整肽的转运不依赖于钠离子。此外，似乎完整的二肽甘氨酰 - L - 亮氨酸至少有两条进入途径，其中只有一条与甘氨酰 - L - 脯氨酸共用。
