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

光合作用机构在适应不同光环境的过程中发生重组。已知，在植物对强光的适应过程中，捕光的叶绿素a/b蛋白复合体分解，伴随着光系统II核心复合体的增加。为了研究光系统重组的机制，用分离的叶绿体研究了叶绿素与脱辅基蛋白的组装。当14C-叶绿素b与叶绿体在植基焦磷酸存在下孵育时，14C-叶绿素b被酯化，部分14C-叶绿素b通过7-羟甲基叶绿素转化为14C-叶绿素a。这些14C-叶绿素a和b被结合到叶绿素-蛋白质复合体中。光系统II的捕光叶绿素a/b-蛋白质复合体的14C-叶绿素a/14C-叶绿素b比值较低，而P700-叶绿素a-蛋白质复合体的比值较高，表明本系统中的叶绿素与脱辅基蛋白具有特异性结合。7-羟甲基叶绿素是从叶绿素b到叶绿素a的中间分子，不能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蛋白复合体中释放出来，并通过脂双层中的7-羟甲基叶绿素转化为叶绿素b，用于形成光系统的核心复合体。

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.