Mechanism of exchange of cytochrome b5 between phosphatidylcholine vesicles.
Mechanism of exchange of cytochrome b5 between phosphatidylcholine vesicles.
复制标题
磷脂酰胆碱囊泡之间细胞色素 b5 的交换机制。
作者：
T. Leto;M. Roseman;P. W. Holloway
用荧光猝灭法研究了细胞色素b5的囊泡间交换。细胞色素b5与1，2-双（9，10-二溴硬脂酰）-sn-甘油-3-磷酸胆碱囊泡的结合导致细胞色素b5荧光猝灭，而与1-棕榈酰-2-油酰-sn-甘油-3-磷酸胆碱囊泡结合后荧光增强。结合时细胞色素b5荧光的这种差异用于研究“淬灭”和“增强”囊泡之间细胞色素b5囊泡间交换的动力学。通过密度梯度离心分离两种细胞色素b5囊泡复合物，为细胞色素b5囊泡间交换提供了直接证据。荧光测定和密度梯度测定都产生相同的值的细胞色素b5交换的程度，平衡后获得的，两种类型的囊泡之间。这两个实验也表明，细胞色素b5结合在一个可逆的方式，并具有相同的亲和力的两种类型的囊泡。交换过程的动力学与涉及细胞色素b5通过水相转移的机制一致，并排除了涉及囊泡碰撞的机制。
The intervesicle exchange of cytochrome b5 has been studied by fluorescence quenching. The binding of cytochrome b5 to 1,2-bis(9.10-dibromostearoyl)-sn-glycerol-3-phosphorylcholine vesicles results in a quenching of cytochrome b5 fluorescence whereas the fluorescence is enhanced upon binding to 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphorylcholine vesicles. This difference in cytochrome b5 fluorescence upon binding was used to study the kinetics of cytochrome b5 intervesicle exchange between the "quenching" and "enhancing" vesicles. Separation of the two cytochrome b5-vesicle complexes by density gradient centrifugation provided direct evidence for cytochrome b5 intervesicle exchange. Both the fluorescence assay and the density gradient assay yield the same value for the extent of cytochrome b5 exchange, obtained after equilibration, between the two types of vesicles. Both experiments also indicate that cytochrome b5 binds in a reversible fashion and has an equal affinity for the two types of vesicles. The kinetics of the exchange process are consistent with a mechanism involving the transfer of cytochrome b5 through the aqueous phase and rule out a mechanism involving vesicle collision.