Substrate-dependent transport of the NADPH:protochlorophyllide oxidoreductase into isolated plastids.

Reinbothe, Steffen; Runge, Sönke; Reinbothe, Christiane; Cleve, Barbara van; Apel, Klaus

doi:10.1105/tpc.7.2.161

Cited by 109 publications

(99 citation statements)

References 60 publications

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“…This idea is supported by the fact that POR-A is imported into plastids in a protochlorophyllide dependent way (Reinbothe et al 1995(Reinbothe et al , 1996.…”

Section: Light-dependent Protochlorophyllide Oxidoreductasesupporting

confidence: 58%

A short overview of chlorophyll biosynthesis in algae

et al. 2008

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Chlorophylls are the most abundant classes of natural pigments and their biosynthesis is therefore a major metabolic activity in the ecosphere. Two pathways exist for chlorophyll biosynthesis, one taking place in darkness and the other requiring continuous light as a precondition. The key process for Chl synthesis is the reduction of protochlorophyllide (Pchlide). This enzymatic reaction is catalysed by two different enzymes -DPOR (dark-operative Pchlide oxidoreductase) or the structurally distinct LPOR (light-dependent Pchlide oxidoreductase). DPOR which consists of three subunits encoded by three plastid genes in eukaryotes was subject of our study. A short overview of our present knowledge of chlorophyll biosynthesis in Chlamydomonas reinhardtii in comparison with other plants is presented.

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“…This idea is supported by the fact that POR-A is imported into plastids in a protochlorophyllide dependent way (Reinbothe et al 1995(Reinbothe et al , 1996.…”

Section: Light-dependent Protochlorophyllide Oxidoreductasesupporting

confidence: 58%

A short overview of chlorophyll biosynthesis in algae

et al. 2008

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“…However, if the effect is physiological, Walker and Willows (1997) have suggested that the results can be reconciled if the buildup of intermediates inhibits the import of one or more of the Mg-chelatase subunits into the chloroplasts. Such a mechanism has been proposed for the regulation of protochlorophyllide reductase import (Reinbothe et al, 1995).…”

Section: Discussionmentioning

confidence: 99%

Magnesium-Chelatase from Developing Pea Leaves1

1998

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Mg-chelatase catalyzes the ATP-dependent insertion of Mg 2؉ into protoporphyrin-IX to form Mg-protoporphyrin-IX. This is the first step unique to chlorophyll synthesis, and it lies at the branch point for porphyrin utilization; the other branch leads to heme. Using the stromal fraction of pea (Pisum sativum L. cv Spring) chloroplasts, we have prepared Mg-chelatase in a highly active (1000 pmol 30 min ؊1 mg ؊1 ) and stable form. The reaction had a lag in the time course, which was overcome by preincubation with ATP. The concentration curves for ATP and Mg 2؉ were sigmoidal, with apparent K m values for Mg 2؉ and ATP of 14.3 and 0.35 mM, respectively. The K m for deuteroporphyrin was 8 nM. This K m is 300 times lower than the published porphyrin K m for ferrochelatase. The soluble extract was separated into three fractions by chromatography on blue agarose, followed by size-selective centrifugal ultrafiltration of the column flow-through. All three fractions were required for activity, clearly demonstrating that the plant Mg-chelatase requires at least three protein components. Additionally, only two of the components were required for activation; both were contained in the flow-through from the blue-agarose column.The biosynthesis of heme and chlorophyll are integral parts of chloroplast development and the acquisition of photosynthetic capacity. Both end products are required in specific but vastly different amounts and are synthesized within the chloroplast via a common tetrapyrrole biosynthetic pathway (Beale and Weinstein, 1990;Porra, 1997). The branch point for the formation of chlorophyll and heme is the use of Proto by the two enzymes that catalyze metal insertion. Ferrochelatase catalyzes the insertion of Fe 2ϩ into Proto, whereas Mg-chelatase catalyzes the insertion of Mg 2ϩ into Proto. Because the flux of common precursors to the respective end products is likely to be controlled by modulation of the branch-point enzymes, we were interested in the properties of these enzymes. This report describes the properties of a totally soluble enzyme system from pea (Pisum sativum L. cv Spring) chloroplasts that catalyzes the Mg-chelatase reaction.Previous work has shown that Mg-chelatase activity requires ATP (Pardo et al., 1980; Walker and Weinstein, 1991b). Although the reaction is formally similar to the ferrochelatase reaction, insertion of a divalent cation into Proto, there is no ATP requirement for the Fe-insertion reaction. Our previous work has shown that the Mgchelatase reaction requires at least two different protein components (Walker and Weinstein, 1991b; Walker et al., 1992). We also showed that the reaction proceeds by a two-step mechanism, involving activation followed by Mg 2ϩ insertion; both steps require ATP (Walker and Weinstein, 1994). This hypothesis was based on the following observations. There is a lag phase in the kinetics that can be overcome by preincubation of the crude enzyme fraction with ATP before the porphyrin substrate is added. ATP␥S can substitute for ATP in the preincubatio...

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“…In angiosperms such as barley, Arabidopsis (1, 2), tobacco (3) and Amaranthus tricolor (4), and gymnosperms such as pine species (5-7), several por gene families were identified that encode highly conserved POR polypeptides. PORA represents the negatively light-regulated POR enzyme whose level drops as a result of the concerted effect of light at the levels of transcription, mRNA stability, plastid import, and protein degradation after light-induced catalysis (8)(9)(10)(11). PORB, the second POR protein identified in barley and Arabidopsis (1,12), is constitutively expressed in darkgrown, illuminated, and light-adapted plants (see ref.…”

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confidence: 99%