Theg S M, Bauerle C, Olsen L J, Selman B R, Keegstra K
Department of Botany, University of Wisconsin, Madison 53706.
J Biol Chem. 1989 Apr 25;264(12):6730-6.
The energy requirements for the import of nuclear-encoded proteins into isolated chloroplasts have been reinvestigated. We have shown that, in contrast to protein import into mitochondria, the translocation of the precursors to ferredoxin, plastocyanin (prPC) and the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (prSS) across all chloroplastic membranes is independent of a protonmotive force and requires only ATP. This extends previous works in which investigations were limited to prSS and demonstrates that our results are probably general to all chloroplastic protein precursors. Our results are particularly interesting for the import of prPC, since in addition to the two envelope membranes, this protein must traverse the energy-transducing thylakoid membranes en route to its proper location in the thylakoid lumen. This lack of involvement of a protonmotive force, specifically of a transmembrane electric potential, demonstrates that separate mechanisms operate during the import of proteins into chloroplasts and mitochondria. We also examined the question of whether ATP is utilized inside or outside of chloroplasts during protein import. Previous attempts to resolve this question have resulted in conflicting answers. We found, by two independent approaches, that ATP for protein import is utilized inside chloroplasts. The implications of these results on the possible mechanisms of protein import into chloroplasts are discussed.
对将核编码蛋白导入分离叶绿体的能量需求进行了重新研究。我们已经表明，与蛋白导入线粒体不同，铁氧化还原蛋白、质体蓝素（prPC）和1,5-二磷酸核酮糖羧化酶/加氧酶小亚基（prSS）的前体穿过所有叶绿体膜的转运不依赖于质子动力，仅需要ATP。这扩展了先前的研究工作，之前的研究仅限于prSS，并表明我们的结果可能适用于所有叶绿体蛋白前体。我们的结果对于prPC的导入特别有趣，因为除了两层包膜膜之外，这种蛋白在到达类囊体腔中其正确位置的途中还必须穿过能量转换类囊体膜。这种质子动力，特别是跨膜电势的不参与，表明在将蛋白导入叶绿体和线粒体的过程中存在不同的机制。我们还研究了在蛋白导入过程中ATP是在叶绿体内还是外被利用的问题。先前解决这个问题的尝试得出了相互矛盾的答案。我们通过两种独立的方法发现，用于蛋白导入的ATP是在叶绿体内被利用的。讨论了这些结果对蛋白导入叶绿体可能机制的影响。
