Evolution of cyanelles deduced from constituents of cyenelle envelopes of a glaucocystophyte, Cyanophora paradoxa

异藻拥有一种特殊的细胞器，即进行含氧光合作用的小藻。真核光合生物的叶绿体被假设是由蓝藻的祖先通过内共生建立的。由于藻青仍然保留了蓝藻的一些共同特征，因此对藻青胞质体包膜的研究将为阐明内生蓝藻质体的进化过程提供一些依据。在本研究项目中，我们分离并表征了异芽胞杆菌的囊膜，并与蓝藻和植物叶绿体的特征进行了比较。用溶菌酶处理分离的完整小胞，用法压细胞法分离。采用蔗糖梯度浮选离心法从匀浆中纯化包膜膜。分离出两个黄色馏分。其中一个部分的浮力密度为1.12 g/cm^3，富含玉米黄质。这与内包膜相对应。浮力密度<1.00 g/cm^3的部分则富含β-胡萝卜素。然而，通过电镜观察，该组分未显示膜状结构。结果表明，该组分不含包膜。对类囊体膜进行洗洁剂处理后，发现仍有黄色部分残留。它富含玉米黄质，浮力密度估计为1.18 g/cm^3，因此估计是一个外包膜。外包膜在蛋白质组成上与外包膜相似，而在浮力密度和对洗涤剂的不溶性上与蓝藻相似。另一方面，内包膜的蛋白质组成与蓝藻的质膜相似。结果表明，蓝藻与植物的包膜具有嵌合性。

Cyanophora paradoxa posseses a special organelle, a cyanelle, which performs oxygenic photosynthesis. Chloroplasts of eukaryotic photosynthetic organisms are hypothesized to be established by endosymbiosis by a progenitor of cyanobacteria. Investigation of plastid envelope of cyanelles of C.paradoxa will provide some crue to elucidate the evolutionary processes of plastids from endosymbiotic cyanobacteria, sice cyanelles stil preserve some characteristics common to cyanobacteria. In the present research project, we have isolated and characterized envelope membranes from C.paradoxa cyanelles and compared characteristics with those of cyanobacteria and plant chloroplasts.Isolated intact cyanelles were treated with lysozyme and raptured by French Pressure cell treatment. Envelope membranes were purified from the homogenate by sucrose gradient floatation centrifugation. Two yellow fractions were separated. One fraction has a buoyant density of 1.12 g/cm^3 and rich in zeaxanthin. This corresponded to inner envelope membranes. Another fraction with a buoyant density of <1.00 g/cm^3 was rich in β-carotene. This fraction however, did not show membranous structures by observation with electron microscopy. It was concluded that the fraction does not contain envelope membanes.A yellow fraction was found to be remained after detergent treatment of thylakoid membranes. This was rich in zeaxanthin with an estimated buoyant density of 1.18 g/cm^3, and thus estimated to be an outer envelope membranes.The outer envelope membranes have an affinity to that of outer envelope membranes in protein composition, while to that of cyanobacteria in buoyant density and insolubility to detergent. On ther other hand, the protein composition of inner envelope membranes was similar to that of plasma membranes of cyanobactria. The results indicate that the envelope membranes have chimeric nature between cyanobacteria and plants.