Umakoshi H, Yoshimoto M, Shimanouchi T, Kuboi R, Komasawa I
Department of Chemical Science and Engineering, Graduate School of Engineering Science, Osaka University, 1-3 Machikaneyamacho, Toyonaka, Osaka 560-0043, Japan.
Biotechnol Prog. 1998 Mar-Apr;14(2):218-26. doi: 10.1021/bp9800135.
The possibility of the translocation of the enzyme across the phospholipid bilayer membrane was investigated by using the liposomes prepared by 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) in which beta-galactosidase (beta-gal) was entrapped. Exposing the POPC liposomes entrapping beta-gal inside to heat treatment (40-50 degrees C, 1-60 min) was found to induce its translocation across the liposome membrane. The translocated activity of beta-gal from inner to outer aqueous phase of liposomes indicated the maximal value when the liposomes entrapping beta-gal were heated at 45 degrees C for 30 min. The gel permeation profiles of the liposomes before and after heat treatment (45 degrees C, 30 min) also supported the translocation of beta-gal across the liposome membrane. The membrane fluidity of liposomes was found to be increased with increasing temperature, so that the hydrophobicity of liposome membrane was also increased. The local hydrophobicity of beta-gal was maximized at the temperature of 40-50 degrees C. The mechanisms of beta-gal translocation have been suggested to be triggered by the enhancement of hydrophobic interaction between the liposome surface and beta-gal molecules. Finally, a minimal scheme of possible mechanism on the heat-induced translocation of beta-gal has been presented on the basis of the hydrophobic interaction between the liposome and the proteins. The experimental data on the heat-induced translocation of beta-gal were well corresponding to those from model calculation.
通过使用由1-棕榈酰-2-油酰-sn-甘油-3-磷酸胆碱（POPC）制备的脂质体来研究该酶跨磷脂双分子层膜转运的可能性，其中包裹了β-半乳糖苷酶（β-gal）。发现将包裹有β-gal的POPC脂质体进行热处理（40-50℃，1-60分钟）会诱导其跨脂质体膜转运。当包裹有β-gal的脂质体在45℃加热30分钟时，β-gal从脂质体内部到外部水相的转运活性显示出最大值。热处理（45℃，30分钟）前后脂质体的凝胶渗透谱也支持β-gal跨脂质体膜的转运。发现脂质体的膜流动性随温度升高而增加，因此脂质体膜的疏水性也增加。β-gal的局部疏水性在40-50℃的温度下达到最大值。已提出β-gal转运的机制是由脂质体表面与β-gal分子之间疏水相互作用的增强所触发。最后，基于脂质体与蛋白质之间的疏水相互作用，提出了关于热诱导β-gal转运可能机制的最简方案。β-gal热诱导转运的实验数据与模型计算的数据非常吻合。
