Adibi S A, Soleimanpour M R
J Clin Invest. 1974 May;53(5):1368-74. doi: 10.1172/JCI107685.
The present studies were performed to determine whether dipeptide absorption in human jejunum exhibits the characteristics of carrier-mediated transport. 15-cm jejunal segments from human volunteers were perfused with test solutions containing varying amounts of either glycylglycine, glycylleucine, glycine, leucine, glycylglycine with leucine or glycine, glycylglycine with glycylleucine, or glycylleucine with an equimolar mixture of free glycine and leucine. Jejunal absorption rates of both glycylglycine and glycylleucine followed the kinetics of a saturable process. The K(m) value in millimoles/liter of glycylglycine was significantly greater than the K(m) value of glycylleucine (43.3+/-2.6 vs. 26.8+/-5.9, P < 0.05); and the K(m) value of glycine was also significantly greater than the K(m) value of leucine (42.7+/-7.5 vs. 20.4+/-5.4, P < 0.05). While overlapping occurred among the K(m) values of free amino acids and dipeptides, the transport kinetics of dipeptides were characterized by higher V(max) values (in micromoles per minute per 15 centimeters) than those of free amino acids. For example, the V(max) values for glycylglycine and glycine were 837+/-62 and 590+/-56, respectively (P < 0.02). While jejunal absorption rates of glycylglycine were not significantly affected by free leucine or free glycine, they were competitively inhibited by glycylleucine. The jejunal absorption rate of glycylleucine was not significantly altered by an equimolar mixture of free glycine and leucine. The selective absorption of dipeptides was investigated by infusing three equimolar mixtures, each containing two different dipeptides. Among the three dipeptides examined, glycylglycine was the least absorbed. There was no significant difference between the absorption of glycylleucine and leucylglycine. The above studies suggest that absorption of both glycylglycine and glycylleucine is mediated by a carrier which is not shared with free neutral amino acids; and that both COOH- and NH(2)-terminal amino acids appear to be influential in imposing the affinity of a dipeptide for the absorption sites.
进行本研究以确定人空肠中双肽吸收是否具有载体介导转运的特征。用含有不同量甘氨酰甘氨酸、甘氨酰亮氨酸、甘氨酸、亮氨酸、甘氨酰甘氨酸与亮氨酸、甘氨酸与甘氨酰甘氨酸、甘氨酰甘氨酸与甘氨酰亮氨酸或甘氨酰亮氨酸与游离甘氨酸和亮氨酸等摩尔混合物的测试溶液灌注人类志愿者的15厘米空肠段。甘氨酰甘氨酸和甘氨酰亮氨酸的空肠吸收率均遵循可饱和过程的动力学。甘氨酰甘氨酸的K(m)值（毫摩尔/升）显著大于甘氨酰亮氨酸的K(m)值（43.3±2.6对26.8±5.9，P<0.05）；甘氨酸的K(m)值也显著大于亮氨酸的K(m)值（42.7±7.5对20.4±5.4，P<0.05）。虽然游离氨基酸和双肽的K(m)值之间存在重叠，但双肽的转运动力学特征是V(max)值（每15厘米每分钟微摩尔数）高于游离氨基酸。例如，甘氨酰甘氨酸和甘氨酸的V(max)值分别为837±62和590±56（P<0.02）。虽然甘氨酰甘氨酸的空肠吸收率不受游离亮氨酸或游离甘氨酸的显著影响，但受甘氨酰亮氨酸竞争性抑制。甘氨酰亮氨酸的空肠吸收率未因游离甘氨酸和亮氨酸的等摩尔混合物而显著改变。通过输注三种等摩尔混合物（每种混合物包含两种不同的双肽）研究了双肽的选择性吸收。在所检测的三种双肽中，甘氨酰甘氨酸吸收最少。甘氨酰亮氨酸和亮氨酰甘氨酸的吸收之间没有显著差异。上述研究表明，甘氨酰甘氨酸和甘氨酰亮氨酸的吸收均由一种不与游离中性氨基酸共用的载体介导；并且COOH-末端和NH(2)-末端氨基酸似乎都对双肽与吸收位点的亲和力有影响。
