The regulatory mechanisms for maintaining the chlorophyll to apoproteins ratio.

当黄化幼苗被光照时，叶绿素（Chl）开始合成，并伴随Chl-蛋白复合物（CP）脱辅基蛋白的积累。新合成的Chl与脱辅基蛋白结合形成CP，CP与其它组分结合形成功能性光系统，每个CP都由Chl与脱辅基蛋白按一定比例组成。已经表明，捕光叶绿素a/b-PSII蛋白复合物结合15 Chl。据报道，通过SDS-PAGE分离的P700-Chla-蛋白复合物的Chl/P700比率为120。PSII核心的两种脱辅基蛋白都有一定的Chl/apoproteins比值。考虑到所有Chl分子都与类囊体膜上的脱辅基蛋白结合，这表明成熟叶绿体的Chl/apoproteins比值是恒定的，过量的Chl或不结合的脱辅基蛋白的积累对叶绿体是不利的。脱辅基蛋白的积累必须根据叶绿素合成速率的变化进行调节。我们把注意力集中在叶绿体发育过程中维持叶绿素与脱辅基蛋白比例恒定的调控机制上，并阐明了以下内容。（1）Chl以两种方式提供给脱辅基蛋白：通过分配新合成的Chl和通过重新分配先前并入其他CP的Chl。（2）不同CP的形成受到脱辅基蛋白对Chl的不同亲和力的调节。（3）叶绿素与CP脱辅基蛋白的协同积累是通过快速消化不与叶绿素结合的脱辅基蛋白实现的。

When etiolated seedlings are illuminated,chlorophyll(Chl)begins to be synthesized with accumulation of Chl-protein complex(CP)apoproteins. Newly synthesized Chl is incorporated into apoproteins to form CPs,which are associated with other components to form functional photosystems.Each CP is supposed to be composed of Chl and its apoprotein in a definite ratio. It have been shown that light-harvesting Chl a/b-protein complex of PSII binds 15 Chl. The Chl/P700 ratio for P700-Chl a-protein complex isolated by SDS-PAGE was reported to be 120. Two apoproteins of PSII core have definite ratios of Chl to apoproteins Taking into consideration the observation that all the Chl molecules bind to apoproteins in thylakoid membranes,these indicate that the ratio of Chl to apoproteins of mature chloroplasts would be kept constant.Accumulation of excess Chl or apoproteins which do not bind with each other would not be favorable for chloroplasts. The accumulation of apoproteins must be regulated in accordance with changes in the rate of Chl synthesis. We focussed our attention on the regulatory mechanisms operate to maintain the Chl to apoprotein ratio constant during chloroplast development and the followings were elucidated.(1)Chl is supplied to apoproteins in two ways:by distribution of newly synthesized Chl and by redistribution of Chl that have been previously incorporated into other CPs. (2)The formation of different CPs is regulated by differential affinities of the apoproteins for Chl.(3)Coordinate accumulation of Chl and apoproteins of CPs is achieved through rapid digestion of apoproteins which are not bound with Chl.