Cheeseman C I, Parsons D S
J Physiol. 1976 Nov;262(2):459-76. doi: 10.1113/jphysiol.1976.sp011605.
The characteristics have been investigated of the transfer into the vascular bed of L-leucine and glycine from free amino acids or peptides in the intestinal lumen of Rana pipiens. Over the concentration range 0-5-10 mM the transfer of L-leucine is but little affected by the presence of equimolar concentrations of glycine but the transfer of glycine, in contrast, is greatly inhibited by the presence of L-leucine. 2. With glycyl-L-leucine in the intestinal lumen, the rate of transfer of glycine into the vascular bed is much greater than from the mixture of the two amino acids and is equal to that of the L-leucine. From L-leucyl-glycine the rates of transfer of leucine and of glycine are also higher than from the mixture of the two amino acids but the rate of transfer of glycine is somewhat lower than that of leucine. There is no evidence of the presence of the dipeptides in the effluent from the portal vein. 3. When the peptide glycyl-L-leucine is added to the lumen in the presence of 10 mM concentrations of the free amino acids, additional amounts of L-leucine and of glycine are transferred in approximately equimolar quantities into the vascular bed. This additional transfer exhibits saturation with respect to concentration of peptide in the intestinal lumen. An additional transfer of amino acids was also found when L-leucyl-glycine was added to the lumen in the presence of saturating concentrations of the two amino acids. 4. Evidence is presented that the presence of the dipeptides in the intestinal lumen had little effect on the transfer of free amino acids from the lumen into the vascular bed. Although the transfer of free amino acids from the lumen into the vascular bed is significantly, but not completely, abolished when the Na in the intestinal lumen is replaced by K, the transfer of the amino acids from the dipeptides is but little affected. 5. The findings are discussed in relation to the view that the dipeptides are transported into the mucosal epithelium by a process that is distinct from those promoting uptake of the individual amino acids. Being completely hydrolysed, there is no evidence for an accumulative uptake of the peptides; it is suggested that this may be related to the fact that the peptide uptake occurs in the absence of Na in the intestinal lumen.
研究了豹蛙肠腔中游离氨基酸或肽中的L-亮氨酸和甘氨酸向血管床的转运特性。在0.5 - 10 mM的浓度范围内，等摩尔浓度的甘氨酸的存在对L-亮氨酸的转运影响很小，但相反，L-亮氨酸的存在会极大地抑制甘氨酸的转运。2. 当肠腔中有甘氨酰-L-亮氨酸时，甘氨酸向血管床的转运速率远高于两种氨基酸混合物的转运速率，且与L-亮氨酸的转运速率相当。从亮氨酰-甘氨酸中，亮氨酸和甘氨酸的转运速率也高于两种氨基酸混合物的转运速率，但甘氨酸的转运速率略低于亮氨酸。门静脉流出液中没有二肽存在的证据。3. 当在10 mM浓度的游离氨基酸存在下将肽甘氨酰-L-亮氨酸添加到肠腔中时，额外量的L-亮氨酸和甘氨酸以近似等摩尔量转运到血管床中。这种额外的转运相对于肠腔中肽的浓度表现出饱和性。当在两种氨基酸饱和浓度存在下将亮氨酰-甘氨酸添加到肠腔中时，也发现了氨基酸的额外转运。4. 有证据表明肠腔中二肽的存在对游离氨基酸从肠腔向血管床的转运影响很小。尽管当肠腔中的Na被K取代时，游离氨基酸从肠腔向血管床的转运显著但未完全消除，但二肽中氨基酸的转运几乎不受影响。5. 结合二肽通过与促进单个氨基酸摄取不同的过程转运到黏膜上皮的观点对这些发现进行了讨论。由于二肽被完全水解，没有证据表明肽有累积摄取；有人认为这可能与肽摄取在肠腔中无Na的情况下发生这一事实有关。
