Holtorf H, Reinbothe S, Reinbothe C, Bereza B, Apel K
Institute of Plant Sciences, Swiss Federal Institute of Technology (ETH), Zurich.
Proc Natl Acad Sci U S A. 1995 Apr 11;92(8):3254-8. doi: 10.1073/pnas.92.8.3254.
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.
NADPH-原叶绿素酸酯氧化还原酶（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步骤，即将原叶绿素酸酯（Pchlide）还原为叶绿素酸酯。在大麦中，鉴定出了两种不同的具有免疫反应性的POR蛋白。与迄今为止研究的光敏感POR酶（POR-A）不同，第二种POR蛋白的水平在幼苗从暗生长转变为光照以及在绿色植物中保持恒定。通过分离和测序编码与POR-A氨基酸序列同一性为75%的第二种POR多肽（POR-B）的cDNA，证实了第二种与POR相关蛋白的存在。在NADPH和Pchlide存在的情况下，体外合成的POR-A和POR-B蛋白可以重构为三元酶活性复合物，该复合物仅在光照后将Pchlide还原为叶绿素酸酯。尽管这两种酶的体外活性相似，但它们的基因在黄化幼苗向绿色幼苗的光诱导转变过程中的表达是不同的。在黑暗生长的幼苗光照期间，POR-A mRNA迅速下降并很快消失，而POR-B mRNA在黑暗生长和绿色幼苗中保持在大致恒定的水平。因此，这些结果表明叶绿素合成由两种光依赖的POR酶控制，一种仅在光照开始时在黄化幼苗中短暂活跃，另一种也在绿色植物中起作用。
