Giudicelli J, Delque-Bayer P, Sudaka P, Poiree J C
Laboratoire de Biochimie, Faculté de Médecine, Nice, France.
Am J Physiol. 1998 Apr;274(4):R1150-7. doi: 10.1152/ajpregu.1998.274.4.R1150.
To reinvestigate the "hydrolase-related transport" concept, neutral alpha-D-glucosidase, a membrane-bound disaccharidase of renal proximal tubule, was first purified from brush-border membranes and then asymmetrically reincorporated into egg phosphatidylcholine vesicles. Proteolytic treatments and immunotitration studies demonstrated that this enzyme was integrated in native and artificial membrane vesicles with a similar topology. The uptake of free glucose and glucose produced by maltose hydrolysis was studied using 1) proteoliposomes containing integrated neutral alpha-D-glucosidase, in combination with other membrane proteins, and 2) proteoliposomes containing only the other membrane proteins but incubated in a medium containing neutral alpha-D-glucosidase in its hydrophilic form. No modification was observed in the uptake of free D-glucose or D-glucose produced by maltose hydrolysis, regardless of enzyme localization. In contrast to previous findings on the hydrolase-related transport concept, these results rule out any participation of neutral alpha-D-glucosidase in the transport of free glucose or glucose produced by maltose hydrolysis. Hydrolytic activity and transmembrane transport appear to be two independent and sequential steps.
为了重新研究“水解酶相关转运”的概念，中性α-D-葡萄糖苷酶，一种肾近端小管的膜结合二糖酶，首先从刷状缘膜中纯化出来，然后不对称地重新整合到卵磷脂囊泡中。蛋白水解处理和免疫滴定研究表明，这种酶以相似的拓扑结构整合到天然和人工膜囊泡中。使用1）含有整合的中性α-D-葡萄糖苷酶以及其他膜蛋白的蛋白脂质体，以及2）仅含有其他膜蛋白但在含有亲水性形式的中性α-D-葡萄糖苷酶的培养基中孵育的蛋白脂质体，研究了游离葡萄糖和麦芽糖水解产生的葡萄糖的摄取。无论酶的定位如何，在游离D-葡萄糖或麦芽糖水解产生的D-葡萄糖的摄取中均未观察到修饰。与先前关于水解酶相关转运概念的发现相反，这些结果排除了中性α-D-葡萄糖苷酶在游离葡萄糖或麦芽糖水解产生的葡萄糖转运中的任何参与。水解活性和跨膜转运似乎是两个独立且连续的步骤。
