2 ROUTES OF CHLOROPHYLLIDE SYNTHESIS THAT ARE DIFFERENTIALLY REGULATED BY LIGHT IN BARLEY (HORDEUM-VULGARE L)
2 ROUTES OF CHLOROPHYLLIDE SYNTHESIS THAT ARE DIFFERENTIALLY REGULATED BY LIGHT IN BARLEY (HORDEUM-VULGARE L)
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DOI：
10.1073/pnas.92.8.3254
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发表时间：
1995-04-11
影响因子：
11.1
通讯作者：
APEL, K
中科院分区：
文献类型：
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作者：
HOLTORF, H;REINBOTHE, S;APEL, K
nadph -原叶绿素氧化还原酶（POR; EC 1.6.99.1）催化高等植物叶绿素合成中唯一已知的光依赖性步骤，原叶绿素（Pchlide）还原为叶绿素内酯。在大麦中，鉴定出两种不同的免疫反应性POR蛋白，与迄今为止研究的光敏POR酶（POR- a）相反，第二种POR蛋白在幼苗从黑暗生长到光明生长的过渡期间和绿色植物中保持不变。通过分离和测序编码第二个POR多肽（POR- b）的cdna，证实了第二个POR相关蛋白的存在，该蛋白的氨基酸序列与POR- a的同源性为75%。在NADPH和Pchlide存在的情况下，体外合成的Pchlide - a和Pchlide - b蛋白只有在光照后才能重组为具有酶活性的三元复合物，将Pchlide还原为叶绿素内酯。尽管这两种酶的体外活性相似，但它们的基因在黄化向绿色幼苗的光诱导转化过程中的表达是不同的。在暗生幼苗中，POR-A mRNA在光照下迅速下降并消失，而POR-B mRNA在暗生幼苗和绿色幼苗中保持大致恒定的水平。因此，这些结果表明叶绿素合成是由两种依赖光的POR酶控制的，其中一种酶仅在光照开始时在黄化幼苗中短暂活跃，另一种酶也在绿色植物中起作用。
NADPH-protochlorophyllide oxidoreductase (POR; EC 1.6.99.1) catalyzes the only known light-dependent step in chlorophyll synthesis of higher plants, the reduction of protochlorophyllide (Pchlide) to chlorophyllide. In barley, two distinct immunoreactive POR proteins were identified, In contrast to the light-sensitive POR enzyme studied thus far (POR-A), levels of the second POR protein remained constant in seedlings during the transition from dark growth to the light and in green plants. The existence of a second POR-related protein was verified by isolating and sequencing cDNAs that encode a second POR polypeptide (POR-B) with an amino acid sequence identity of 75% to the POR-A. In the presence of NADPH and Pchlide, the in vitro-synthesized POR-A and POR-B proteins could be reconstituted to ternary enzymatically active complexes that reduced Pchlide to chlorophyllide only after illumination. Even though the in vitro activities of the two enzymes were similar, the expression of their genes during the light-induced transformation of etiolated to green seedlings was distinct. While the POR-A mRNA rapidly declined during illumination of dark-grown seedlings and soon disappeared, POR-B mRNA remained at an approximately constant level in dark-grown and green seedlings. Thus these results suggest that chlorophyll synthesis is controlled by two light-dependent POR enzymes, one that is active only transiently in etiolated seedlings at the beginning of illumination and the other that also operates in green plants.