Said H M, Ghishan F K, Redha R
Department of Pediatric Gastroenterology, Vanderbilt University School of Medicine, Nashville, TN 37232.
Biochim Biophys Acta. 1988 Jun 22;941(2):232-40. doi: 10.1016/0005-2736(88)90184-8.
Transport of the dipeptide glycine-L-proline (Gly-L-Pro) in the developing intestine of suckling rats and its subsequent maturation in adult rats was examined using the brush-border membrane vesicles (BBMV) technique. Uptake of Gly-L-Pro by BBMV was mainly the result of transport into the intravesicular space with little binding to membrane surfaces. Transport of Gly-L-Pro in BBMV of suckling rats was: (1) Na+ independent; (2) pH dependent with maximum uptake at an incubation buffer pH of 5.0; (3) saturable as a function of concentration (apparent Km = 21.5 +/- 7.9 mM, Vmax = 8.6 +/- 1.5 nmol/mg protein per 10 s); (4) inhibited by other di- and tripeptides; and (5) stimulated and inhibited by inducing a negative and positive intravesicular membrane electrical potential, respectively. Similarly, transport of Gly-L-Pro in intestinal BBMV of adult rats was saturable as a function of concentration (apparent Km = 17.4 +/- 8.6 mM, Vmax = 9.1 +/- 2.1 nmol/mg protein per 10 s) and was stimulated and inhibited by inducing a relatively negative and positive intravesicular membrane potential, respectively. No difference in the transport kinetic parameters of Gly-L-Pro was observed in suckling and adult rats, indicating a similar activity (and/or number) and affinity of the transport carrier in the two age groups. These results demonstrate that the transport of Gly-L-Pro is by a carrier-mediated process which is fully developed at the suckling period. Furthermore, the process is H+-dependent but not Na+-dependent, electrogenic and most probably occurs by a Gly-L-Pro/H+ cotransport mechanism.
采用刷状缘膜囊泡（BBMV）技术，研究了甘氨酸 - L - 脯氨酸（Gly - L - Pro）二肽在乳鼠发育中的肠道中的转运及其在成年大鼠中的后续成熟过程。BBMV对Gly - L - Pro的摄取主要是转运到囊泡内空间的结果，与膜表面的结合很少。Gly - L - Pro在乳鼠BBMV中的转运具有以下特点：（1）不依赖Na⁺；（2）依赖pH，在孵育缓冲液pH为5.0时摄取量最大；（3）随浓度呈饱和状态（表观Km = 21.5±7.9 mM，Vmax = 8.6±1.5 nmol/mg蛋白质每10秒）；（4）受其他二肽和三肽抑制；（5）分别通过诱导囊泡内膜电势为负和正来刺激和抑制。同样，Gly - L - Pro在成年大鼠肠道BBMV中的转运也随浓度呈饱和状态（表观Km = 17.4±8.6 mM，Vmax = 9.1±2.1 nmol/mg蛋白质每10秒），并且分别通过诱导相对负和正的囊泡内膜电势来刺激和抑制。在乳鼠和成年大鼠中未观察到Gly - L - Pro转运动力学参数的差异，表明两个年龄组中转运载体的活性（和/或数量）及亲和力相似。这些结果表明，Gly - L - Pro的转运是由载体介导的过程，在哺乳期已完全发育。此外，该过程依赖H⁺而非Na⁺，是电生的，很可能通过Gly - L - Pro/H⁺共转运机制发生。
