The Regulation of Enzymes Involved in Chlorophyll Biosynthesis

Reinbothe, Steffen; Reinbothe, Christiane

doi:10.1111/j.1432-1033.1996.00323.x

Cited by 125 publications

(54 citation statements)

References 329 publications

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“…The biosynthesis of tetrapyrrole (porphyrins and chlorins) via the C5-pathway, a process taking place entirely in chloroplasts, was found to have three potential thioredoxin-linked members: glutamate-1-semialdehyde 2,1-(GSA)-aminomutase, uroporphyrinogen decarboxylase, and magnesium chelatase. The first of these, glutamate-1-semialdehyde 2,1 aminomutase, catalyzes the formation of ␦-aminolevulinic acid, the first committed precursor of the C5-pathway (21). Other evidence supports such a role for thioredoxin in this series of reactions.…”

Section: Resultsmentioning

confidence: 99%

“…Other evidence supports such a role for thioredoxin in this series of reactions. For example, the activity of glutamate-1-semialdehyde aminomutase in etiolated barley seedlings increases dramatically in the light whereas the level of the corresponding mRNA remains constant (21). Further, it has been observed that DTT alleviates the inhibition of the synthesis of an intermediate of the pathway, protoporphyrin IX under oxidizing conditions (22).…”

Section: Resultsmentioning

confidence: 99%

“…Further, it has been observed that DTT alleviates the inhibition of the synthesis of an intermediate of the pathway, protoporphyrin IX under oxidizing conditions (22). Finally, the second potential target, uroporphyrinogen decarboxylase, catalyzes a reaction in common with heme biosynthesis, and the third, magnesium chelatase, catalyzes the insertion of magnesium, the first dedicated step of chlorophyll synthesis (21) that is considered pivotal to plastid-tonucleus signaling (23,24). The present results thus link chloroplast thioredoxins to the regulation of both tetrapyrrole biosynthesis and nuclear gene expression.…”

Section: Resultsmentioning

confidence: 99%

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Proteomics gives insight into the regulatory function of chloroplast thioredoxins

Balmer

Koller

Val

et al. 2002

Proc. Natl. Acad. Sci. U.S.A.

397

370

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Thioredoxins are small multifunctional redox active proteins widely if not universally distributed among living organisms. In chloroplasts, two types of thioredoxins ( f and m) coexist and play central roles in regulating enzyme activity. Reduction of thioredoxins in chloroplasts is catalyzed by an iron-sulfur disulfide enzyme, ferredoxin-thioredoxin reductase, that receives photosynthetic electrons from ferredoxin, thereby providing a link between light and enzyme activity. Chloroplast thioredoxins function in the regulation of the Calvin cycle and associated processes. However, the relatively small number of known thioredoxin-linked proteins (about 16) raised the possibility that others remain to be identified. To pursue this opportunity, we have mutated thioredoxins f and m, such that the buried cysteine of the active disulfide has been replaced by serine or alanine, and bound them to affinity columns to trap target proteins of chloroplast stroma. The covalently linked proteins were eluted with DTT, separated on gels, and identified by mass spectrometry. This approach led to the identification of 15 potential targets that function in 10 chloroplast processes not known to be thioredoxin linked. Included are proteins that seem to function in plastid-to-nucleus signaling and in a previously unrecognized type of oxidative regulation. Approximately two-thirds of these targets contained conserved cysteines. We also identified 11 previously unknown and 9 confirmed target proteins that are members of pathways known to be regulated by thioredoxin. In contrast to results with individual enzyme assays, specificity for thioredoxin f or m was not observed on affinity chromatography.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Proteomics gives insight into the regulatory function of chloroplast thioredoxins

Balmer

Koller

Val

et al. 2002

Proc. Natl. Acad. Sci. U.S.A.

397

370

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“…A crucial branch point of the tetrapyrrole synthetic pathway in higher plants is the chelation of either Mg 2ϩ to make chlorophyll or Fe 2ϩ for heme catalyzed by magnesium chelatase or ferrochelatase, respectively (38). One model that has been proposed for the control of this branchpoint, based on biochemical studies, is that the two enzymes are spatially separated within the chloroplast, magnesium chelatase being associated with the envelope membrane (39), and ferrochelatase existing exclusively in the thylakoids (40).…”

Section: Discussionmentioning

confidence: 99%

Dual Targeting of Spinach Protoporphyrinogen Oxidase II to Mitochondria and Chloroplasts by Alternative Use of Two In-frame Initiation Codons

Watanabe

Che

Iwano

et al. 2001

Journal of Biological Chemistry

148

118

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Protoporphyrinogen oxidase (Protox) is the final enzyme in the common pathway of chlorophyll and heme biosynthesis. Two Protox isoenzymes have been described in tobacco, a plastidic and a mitochondrial form. We isolated and sequenced spinach Protox cDNA, which encodes a homolog of tobacco mitochondrial Protox (Protox II). Alignment of the deduced amino acid sequence between Protox II and other tobacco mitochondrial Protox homologs revealed a 26-amino acid N-terminal extension unique to the spinach enzyme. Immunoblot analysis of spinach leaf extract detected two proteins with apparent molecular masses of 57 and 55 kDa in chloroplasts and mitochondria, respectively. In vitro translation experiments indicated that two translation products (59 and 55 kDa) are produced from Protox II mRNA, using two in-frame initiation codons. Transport experiments using green fluorescent proteinfused Protox II suggested that the larger and smaller translation products (Protox IIL and IIS) target exclusively to chloroplasts and mitochondria, respectively.

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“…The likelihood that its final destination is the thylakoids is increased by the recent reassignment of another Chl-biosynthetic enzyme, Pchlide reductase, to the thylakoids [54,55]. Interestingly, Pchlide reductase had previously been reported to be on the chloroplast envelopes [48], but this has now been explained as an import intermediate [56], and the final destination of this enzyme is thought to be the thylakoids [54,55]. Only two other porphyrin-biosynthetic enzymes have been reported to be on the envelope : protoporphyrinogen oxidase (which functions in both haem and Chl synthesis) [49] and ferrochelatase [57].…”

Section: Localization Of Mg-chelatase Within the Chloroplastmentioning

confidence: 99%

Mechanism and regulation of Mg-chelatase

Walker

Willows

1997

Biochemical Journal

225

173

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Mg-chelatase catalyses the insertion of Mg into protoporphyrin IX (Proto). This seemingly simple reaction also is potentially one of the most interesting and crucial steps in the (bacterio)chlorophyll (Bchl/Chl)-synthesis pathway, owing to its position at the branch-point between haem and Bchl/Chl synthesis. Up until the level of Proto, haem and Bchl/Chl synthesis share a common pathway. However, at the point of metal-ion insertion there are two choices: Mg2+ insertion to make Bchl/Chl (catalysed by Mg-chelatase) or Fe2+ insertion to make haem (catalysed by ferrochelatase). Thus the relative activities of Mg-chelatase and ferrochelatase must be regulated with respect to the organism's requirements for these end products . How is this regulation achieved? For Mg-chelatase, the recent design of an in vitro assay combined with the identification of Bchl-biosynthetic enzyme genes has now made it possible to address this question. In all photosynthetic organisms studied to date, Mg-chelatase is a three-component enzyme, and in several species these proteins have been cloned and expressed in an active form. The reaction takes place in two steps, with an ATP-dependent activation followed by an ATP-dependent chelation step. The activation step may be the key to regulation, although variations in subunit levels during diurnal growth may also play a role in determining the flux through the Bchl/Chl and haem branches of the pathway.

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The Regulation of Enzymes Involved in Chlorophyll Biosynthesis

Cited by 125 publications

References 329 publications

Proteomics gives insight into the regulatory function of chloroplast thioredoxins

Proteomics gives insight into the regulatory function of chloroplast thioredoxins

Dual Targeting of Spinach Protoporphyrinogen Oxidase II to Mitochondria and Chloroplasts by Alternative Use of Two In-frame Initiation Codons

Mechanism and regulation of Mg-chelatase

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