Rajendran V M, Ansari S A, Harig J M, Adams M B, Khan A H, Ramaswamy K
Gastroenterology. 1985 Dec;89(6):1298-304. doi: 10.1016/0016-5085(85)90646-8.
This study characterizes the transport of [1-14C]glycyl-L-proline into purified brush border membrane vesicles prepared from human small intestine. Time-course uptake curves of glycyl-L-proline were similar under sodium thiocyanate or potassium thiocyanate gradient conditions (extravesicular greater than intravesicular) and did not show any overshoot phenomena. The transport of glycine and proline, however, was stimulated by the presence of sodium gradient. Measurement of peptide uptake with increasing medium osmolarity showed that glycyl-L-proline was transported into an osmotically reactive intravesicular space with insignificant binding to the surface of the vesicles. Only 2% of the glycyl-L-proline in the incubation media was hydrolyzed after 10 min of incubation. Also, there was no hydrolysis of peptide transported into the intravesicular space. The effects of increasing concentrations of glycyl-L-proline on uptake showed that uptake of the peptide was saturable and conformed to Michaelis-Menten kinetics with a Km of 4.1 +/- 0.5 mM and a Vmax of 1.53 +/- 0.07 nmol/mg protein X 0.5 min. Free amino acids did not inhibit the transport of glycyl-L-proline while dipeptides and tripeptides exerted appreciable inhibition (up to 60%). Our results show that human small intestinal brush border membrane vesicles transport glycyl-L-proline as an intact peptide by a carrier-mediated, Na+-independent process.
本研究对[1-¹⁴C]甘氨酰-L-脯氨酸转运至从人小肠制备的纯化刷状缘膜囊泡中的过程进行了表征。在硫氰酸钠或硫氰酸钾梯度条件下（囊泡外浓度高于囊泡内），甘氨酰-L-脯氨酸的时间进程摄取曲线相似，且未显示任何过冲现象。然而，甘氨酸和脯氨酸的转运受到钠梯度的刺激。随着培养基渗透压增加对肽摄取的测量表明，甘氨酰-L-脯氨酸被转运至具有渗透活性的囊泡内空间，与囊泡表面的结合不显著。孵育10分钟后，孵育培养基中只有2%的甘氨酰-L-脯氨酸被水解。此外，转运至囊泡内空间的肽也没有水解。增加甘氨酰-L-脯氨酸浓度对摄取的影响表明，该肽的摄取是可饱和的，符合米氏动力学，Km为4.1±0.5 mM，Vmax为1.53±0.07 nmol/mg蛋白质×0.5分钟。游离氨基酸不抑制甘氨酰-L-脯氨酸的转运，而二肽和三肽则有明显抑制作用（高达60%）。我们的结果表明，人小肠刷状缘膜囊泡通过载体介导的、不依赖Na⁺的过程将甘氨酰-L-脯氨酸作为完整肽进行转运。
