Uroporphyrinogen III Research Articles

GSTU43 gene involved in ALA-regulated redox homeostasis, to maintain coordinated chlorophyll synthesis of tomato at low temperature

BackgroundExogenous 5-aminolevulinic acid (ALA) positively regulates plants chlorophyll synthesis and protects them against environmental stresses, although the protection mechanism is not fully clear. Here, we explored the effects of ALA on chlorophyll synthesis in tomato plants, which are sensitive to low temperature. We also examined the roles of the glutathione S-transferase (GSTU43) gene, which is involved in ALA-induced tolerance to oxidation stress and regulation of chlorophyll synthesis under low temperature.ResultsExogenous ALA alleviated low temperature caused chlorophyll synthesis obstacle of uroporphyrinogen III (UROIII) conversion to protoporphyrin IX (Proto IX), and enhanced the production of chlorophyll and its precursors, including endogenous ALA, Proto IX, Mg-protoporphyrin IX (Mg-proto IX), and protochlorophyll (Pchl), under low temperature in tomato leaves. However, ALA did not regulate chlorophyll synthesis at the level of transcription. Notably, ALA up-regulated the GSTU43 gene and protein expression and increased GST activity. Silencing of GSTU43 with virus-induced gene silencing reduced the activities of GST, superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase, and increased the membrane lipid peroxidation; while fed with ALA significant increased all these antioxidase activities and antioxidant contents, and alleviated the membrane damage.ConclusionsALA triggered GST activity encoded by GSTU43, and increased tomato tolerance to low temperature-induced oxidative stress, perhaps with the assistance of ascorbate- and/or a glutathione-regenerating cycles, and actively regulated the plant redox homeostasis. This latter effect reduced the degree of membrane lipid peroxidation, which was essential for the coordinated synthesis of chlorophyll.

Exogenous spermidine delays chlorophyll metabolism in cucumber leaves (Cucumis sativus L.) under high temperature stress

This study evaluated the effects of exogenous spermidine (Spd) on chlorophyll (Chl) biosynthesis and catabolism in the leaves of cucumber (Cucumis sativus L.) seedlings under high temperature stress. Substrate culture experiments were performed using the high temperature-sensitive variety ‘Jinchun No. 2’ in an artificial climate chamber at 42/32 °C with foliar applications of 1.0 mmol L−1 Spd. The results suggested that high temperature stress markedly reduced the leaf Chl concentrations and inhibited plant growth; the harmful effect of high temperature on the cucumber seedlings was mitigated by exogenous Spd, which increased the leaf Chl concentration and promoted plant growth. Under high temperature stress, the conversion of porphobilinogen (PBG) into uroporphyrinogen III (UroIII) in the Chl biosynthetic pathway and the catabolic process of Chl were accelerated. Following the application of exogenous Spd, the conversion of PBG into UroIII was suppressed, and the accumulation of certain intermediates, e.g., protoporphyrin IX (ProtoIX) and Mg-protoporphyrin IX (Mg-ProtoIX), was decreased in the Chl biosynthetic pathway. Additionally, exogenous Spd reduced chlorophyllase (Chlase) and Mg-dechelatase (MDCase) activity and transcript levels and markedly downregulated pheophorbide A oxygenase (PaO), red Chl catabolite reductase (RCCR), Chl b reductase 1 (CBR1) and stay-green reductase 1 (SGR1) transcript levels. These results indicate that although high temperature stress accelerated Chl biosynthesis, it concurrently facilitated Chl catabolism in cucumber leaves. Exogenous Spd delayed the conversion of PBG into UroIII in the Chl biosynthetic pathway, effectively preventing oxidative bleaching of Chl in cucumber leaves. Meanwhile, Spd clearly decreased PaO pathway-related enzyme activity and transcript levels, thereby slowing Chl catabolism and increasing Chl concentrations.

Alternative pathways for siroheme synthesis in Klebsiella aerogenes.

Siroheme, the cofactor for sulfite and nitrite reductases, is formed by methylation, oxidation, and iron insertion into the tetrapyrrole uroporphyrinogen III (Uro-III). The CysG protein performs all three steps of siroheme biosynthesis in the enteric bacteria Escherichia coli and Salmonella enterica. In either taxon, cysG mutants cannot reduce sulfite to sulfide and require a source of sulfide or cysteine for growth. In addition, CysG-mediated methylation of Uro-III is required for de novo synthesis of cobalamin (coenzyme B(12)) in S. enterica. We have determined that cysG mutants of the related enteric bacterium Klebsiella aerogenes have no defect in the reduction of sulfite to sulfide. These data suggest that an alternative enzyme allows for siroheme biosynthesis in CysG-deficient strains of Klebsiella. However, Klebsiella cysG mutants fail to synthesize coenzyme B(12), suggesting that the alternative siroheme biosynthetic pathway proceeds by a different route. Gene cysF, encoding an alternative siroheme synthase homologous to CysG, has been identified by genetic analysis and lies within the cysFDNC operon; the cysF gene is absent from the E. coli and S. enterica genomes. While CysG is coregulated with the siroheme-dependent nitrite reductase, the cysF gene is regulated by sulfur starvation. Models for alternative regulation of the CysF and CysG siroheme synthases in Klebsiella and for the loss of the cysF gene from the ancestor of E. coli and S. enterica are presented.

Human Uroporphyrinogen-III Synthase: Genomic Organization, Alternative Promoters, and Erythroid-Specific Expression

Uroporphyrinogen-III (URO) synthase is the heme biosynthetic enzyme defective in congenital erythropoietic porphyria. The ∼34-kb human URO-synthase gene (UROS) was isolated, and its organization and tissue-specific expression were determined. The gene had two promoters that generated housekeeping and erythroid-specific transcripts with unique 5′-untranslated sequences (exons 1 and 2A) followed by nine common coding exons (2B to 10). Expression arrays revealed that the housekeeping transcript was present in all tissues, while the erythroid transcript was only in erythropoietic tissues. The housekeeping promoter lacked TATA and SP1 sites, consistent with the observed low level expression in most cells, whereas the erythroid promoter contained GATA1 and NF-E2 sites for erythroid specificity. Luciferase reporter assays demonstrated that the housekeeping promoter was active in both erythroid K562 and HeLa cells, while the erythroid promoter was active only in erythroid cells and its activity was increased during hemin-induced erythroid differentiation. Thus, human URO-synthase expression is regulated during erythropoiesis by an erythroid-specific alternative promoter.

Studies On uro'gen III synthase with modified bilanes

Four new hydroxymethylbilane analogs have been prepared and their activities as substrates/inhibitors of Uroporphyrinogen III synthase investigated.

Involvement of free and enzyme-bound intermediates in the reaction mechanism catalyzed by the bovine liver immobilized porphobilinogen deaminase. Proof that they are substrates for cosynthetase in uroporphyrinogen III biosynthesis.

The detection and accumulation of tetrapyrrole intermediates synthesized by the action of bovine liver porphobilinogen deaminase immobilized to Sepharose 4B is reported. Employing Sepharose-deaminase preparations, two phases in uroporphyrinogen I synthesis as a function of time were observed, suggesting the accumulation of free and enzyme-bound intermediates, the concentration and distribution of which were time dependent. The deaminase-bound intermediate behaves as a substrate in uroporphyrinogen I synthesis whereas the free intermediates produce enzyme inhibition. The tetrapyrrole intermediate bound to the Sepharose-enzyme is removed from the protein by the binding of porphobilinogen. Free as well as enzyme-bound intermediates are shown to be substrates for cosynthetase with formation of 80% uroporphyrinogen III.

Erythrocyte 5-Aminolaevulinic Acid Dehydrase Hydroxymethylbilane Synthase and Uroporphyrinogen Iii Synthase Activities in Alcoholics

Erythrocyte 5-Aminolaevulinic Acid Dehydrase Hydroxymethylbilane Synthase and Uroporphyrinogen Iii Synthase Activities in Alcoholics

Erythrocyte 5-Aminolaevulinic Acid Dehydrase Hydroxymethylbilane Synthase and Uroporphyrinogen Iii Synthase Activities in Alcoholics

Erythrocyte 5-Aminolaevulinic Acid Dehydrase Hydroxymethylbilane Synthase and Uroporphyrinogen Iii Synthase Activities in Alcoholics