Hisanaga H, Iioka H, Moriyama I, Nabuchi K, Morimoto K, Ichijo M
Department of Obstetrics and Gynecology, Nara Medical School, Japan.
Asia Oceania J Obstet Gynaecol. 1991 Mar;17(1):67-72. doi: 10.1111/j.1447-0756.1991.tb00253.x.
To elucidate the mechanism of placental amino acid transport, the transport of amino acids into brush border membrane vesicles was investigated using brush border membrane vesicles (BBMV) separated from the human full-term placenta. 1. The transport of l-alanine and l-glutamine into the brush border membrane vesicles prepared from either early gestational placenta or full-termed placenta disclosed a typical overshooting phenomenon in the presence of H+ concentration gradient (extravesicular pH greater than intravesicular pH). 2. The H(+)-dependent overshooting transport of urea into the brush border membrane vesicles disappeared in the presence of H+ ionophore. 3. The initial velocity of H+ concentration gradient dependent uptake of urea into the brush border membrane vesicles was regulated by the saturation kinetics determined by the concentration of urea. The values of Km and Vmax, calculated as the kinetic parameters of urea transport by reciprocal plotting of the initial velocity of uptake and the concentration of urea, were 10.8 mM and 410 mumol/mg protein/10 sec, respectively. The above results indicate that a transport system which transports urea in exchange for H+ exists in human full-term placental microvillous membrane.
为阐明胎盘氨基酸转运机制，利用从足月人胎盘中分离出的刷状缘膜囊泡（BBMV）研究了氨基酸向刷状缘膜囊泡的转运。1. 在存在H⁺浓度梯度（囊泡外pH大于囊泡内pH）的情况下，l-丙氨酸和l-谷氨酰胺向早期妊娠胎盘或足月胎盘制备的刷状缘膜囊泡中的转运显示出典型的过冲现象。2. 在存在H⁺离子载体的情况下，尿素向刷状缘膜囊泡的H⁺依赖性过冲转运消失。3. 尿素向刷状缘膜囊泡的H⁺浓度梯度依赖性摄取的初始速度受尿素浓度决定的饱和动力学调节。通过摄取初始速度与尿素浓度的倒数作图计算出的尿素转运动力学参数Km和Vmax值分别为10.8 mM和410 μmol/mg蛋白质/10秒。上述结果表明，在足月人胎盘微绒毛膜中存在一种以H⁺交换转运尿素的转运系统。
