Modulation excitation spectrophotometry of purple membrane of Halobacterium halobium
Modulation excitation spectrophotometry of purple membrane of Halobacterium halobium
复制标题
盐杆菌紫色膜的调制激发分光光度法
作者：
M. Slifkin;S. Caplan
当盐生盐杆菌在低氧浓度的光照下生长时，它会合成含有紫色色素的膜。如果暴露在低盐浓度下，细胞膜会解离成蛋白质和色素组成不同的片段，并且可以分离1。这些碎片中最明显的是所谓的“紫膜”2。分离的紫膜含有25%的脂质和75%的蛋白质2;只发现了一种蛋白质，这种蛋白质，细菌视紫红质，显然类似于动物的视觉色素;它含有1摩尔视网膜每摩尔蛋白质结合作为希夫碱的赖氨酸残基3。蛋白质在膜中形成平面晶格4，并在570 nm 3处显示出宽吸收最大值4。光的吸收将570 nm的物质转化为在412 nm处吸收最大的第二种物质，并且在黑暗中在几毫秒内重新转化为570 nm的复合物。这显然伴随着蛋白质的构象变化，它在两种构象之间快速循环，在第一次转换中在膜的一侧释放质子，并在第二次转换中将它们带到另一侧。因此，在完整的细胞中，细菌视紫红质似乎充当光驱动的质子泵6，7。
WHEN Halobacterium halobium is grown at low oxygen concentrations in the light, it synthesises patches of membrane containing a purple pigment. If exposed to low salt concentrations, the cell membrane dissociates into fragments which differ in their protein and pigment composition and can be separated1. The most conspicuous of these fragments is the so-called ‘purple membrane’2. The isolated purple membrane contains 25% lipid and 75% protein2; only a single species of protein has been found. This protein, bacteriorhodopsin, is apparently similar to the animal visual pigment; it contains 1 mol of retinal per mol protein bound as a Schiff base to a lysine residue3. The protein forms a planar lattice in the membrane4 and shows a broad absorption maximum at 570 nm3,4. Absorption of light converts the 570 nm species to a second species which absorbs maximally at 412 nm, and in the dark reconverts to the 570 nm complex within a few milliseconds. This is apparently accompanied by a conformational change in the protein, which cycles rapidly between the two conformations, releasing protons on one side of the membrane in the first transition and taking them up on the other in the second5. Thus, in the intact cells the bacteriorhodopsin seems to act as a light-driven proton pump6,7.