Conversion of Chlorophyll b to Chlorophyll a and the Assembly of Chlorophyll with Apoproteins

光合机构在适应不同光环境的过程中发生重组。据了解，在低光生长的植物适应强光，捕光叶绿素a/b-蛋白质复合物分解伴随着光系统II的核心复合物的增加。为了研究光系统重组的机制，叶绿素与脱辅基蛋白的组装进行了研究。当14 C-叶绿素B与叶绿体在植基焦磷酸盐存在下孵育时，14 C-叶绿素B被酯化，并且一些14 C-叶绿素B通过7-羟甲基叶绿素转化为14 C-叶绿素a。这些14 C-叶绿素a和B被纳入叶绿素-蛋白质复合物。光系统II的捕光叶绿素a/b-蛋白复合物具有较低的14 C-叶绿素a/14 C-叶绿素B比值，而P700-叶绿素a-蛋白复合物具有较高的比值，表明在我们的系统中叶绿素与脱辅基蛋白特异性结合。7-羟甲基叶绿素是从叶绿素B到叶绿素a的中间分子，不组装成任何脱辅基蛋白。这些结果表明，叶绿素B从光系统II的捕光叶绿素a/b-蛋白质复合物中释放，并通过脂双层中的7-羟甲基叶绿素转化为叶绿素B，并用于形成光系统的核心复合物。

Photosynthetic apparatus is reorganized during acclimation to various light environment. It is known that during adaptation of low light grown plants to high light, light-harvesting chlorophyll a/b-protein complexes decomposes concomitant increase in core complexes of photosystem II.In order to study the mechanisms for reorganization of photosystems, assembly of chlorophyll with apoproteins was investigated by isolated chloroplasts. When 14C-chlorophyllide b was incubated with chloroplasts in the presence of phytylpyrophosphate, 14C-chlorophyllide b was esterified and some of the 14C-chlorophyll b was converted to 14C-chlorophyll a via 7-hydroxymethyl chlorophyll. These 14C-chlorophyll a and b were incorporated into chlorophyll-protein complexes. Light-harvesting chlorophyll a/b-protein complexes of photosystem II had lower 14C-chlorophyll a/14C-chlorophyll b ratio and P700-chlorophyll a-protein complexes had higher ratio, indicating the specific binding of chlorophyll to apoproteins in our systems. 7-Hydroxymethyl chlorophyll, an intermediate molecule from chlorophyll b to chlorophyll a, did not assemble to any apoproteins. These results indicate that chlorophyll b releases from light-harvesting chlorophyll a/b-protein complexes of photosystem II and converted to chlorophyll b via 7-hydroxymethyl chlorophyll in lipid bilayr and them used for the formation of core complexes of photosystems.