Coulson R A, Hernandez T
Comp Biochem Physiol A Comp Physiol. 1983;75(3):407-12. doi: 10.1016/0300-9629(83)90102-0.
Seventeen amino acids were fed singly to small caimans and the rates of their disappearance from the gut lumen, and of their appearance in intestinal mucosa, whole intestine, whole stomach, and plasma were determined. The results were compared with those in which massive amounts of protein were fed. When single amino acids were fed, only traces of arginine, ornithine, lysine, aspartate and asparagine were absorbed intact. Glycine, alanine and serine were absorbed rapidly reaching mucosal concentrations as high as 40 mM. The others were not concentrated as highly and most were absorbed by the mucosa more slowly than the glycine group. Protein feeding did not result in high amino acid concentrations in the mucosa. Whether amino acids were ingested as protein or in the free state, glycine, alanine and glutamine increased in the mucosa, suggesting these three incorporate nitrogen released from the others. It appeared that several transport systems operate if amino acids are given singly, and that a different more efficient transport system operates during protein digestion.
将17种氨基酸分别投喂给小凯门鳄，并测定它们从肠腔消失的速率以及在肠黏膜、整个肠道、整个胃和血浆中出现的速率。将结果与投喂大量蛋白质时的结果进行比较。当投喂单一氨基酸时，只有微量的精氨酸、鸟氨酸、赖氨酸、天冬氨酸和天冬酰胺被完整吸收。甘氨酸、丙氨酸和丝氨酸吸收迅速，黏膜浓度高达40 mM。其他氨基酸的浓度没有那么高，大多数氨基酸被黏膜吸收的速度比甘氨酸组慢。投喂蛋白质不会导致黏膜中氨基酸浓度升高。无论氨基酸是以蛋白质形式还是以游离状态摄入，甘氨酸、丙氨酸和谷氨酰胺在黏膜中都会增加，这表明这三种氨基酸结合了其他氨基酸释放的氮。似乎如果单独给予氨基酸，有几种转运系统在起作用，而在蛋白质消化过程中起作用的是一种不同的、更有效的转运系统。
