Tyrosine Aminotransferase Catalyzes the Final Step of Methionine Recycling in
            <i>Klebsiella pneumoniae</i>

Heilbronn, Jacqueline; Wilson, Judith; Berger, Bradley J.

doi:10.1128/jb.181.6.1739-1747.1999

Cited by 38 publications

(18 citation statements)

References 50 publications

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“…Finally, the role of amino acid transaminases in MOB transamination in yeast seems to be an intriguing question, as different isoenzymes may have different roles in different conditions, resulting in a very robust step of the cycle. We have clearly demonstrated that the aromatic and branched chain amino acid transaminases are the main enzymes for this step, similar to the situation in bacteria [12][13][14][15]. Thus, all of the enzymes in the methionine salvage pathway have been identified in a eukaryotic organism.…”

Section: Discussionsupporting

confidence: 66%

A complete inventory of all enzymes in the eukaryotic methionine salvage pathway

Pirkov¹,

Norbeck²,

Gustafsson³

et al. 2008

The FEBS Journal

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Sulfur metabolism has been studied extensively and is, to a large degree, universal for eukaryotes [1][2][3][4]. However, there are still predicted pathways in which all enzymes ⁄ genes have not been identified. Sulfur is needed in the form of the amino acids cysteine and methionine, as well as S-adenosylmethionine, the adenosylated form of methionine. S-adenosylmethionine has many different functions in the cell, including as a starting point for the synthesis of polyamines: putrescine, spermine and spermidine. Polyamines are important for growth, and yeast has an absolute requirement for putrescine and spermidine, as studied in deletion mutants of biosynthetic enzymes [5,6]. During the formation of spermidine and spermine, the metabolite 5¢-methylthioadenosine (MTA) is formed, which contains the sulfur atom of methionine.As the assimilation of sulfur is strongly energy consuming in the form of redox equivalents [2], most organisms from bacteria to mammals and plants have evolved recycling pathways to reuse sulfur and regenerate methionine: the 'methionine salvage pathway' (MTA cycle) [7][8][9][10][11]. The cycle of mammals and yeast consists of six enzymatic steps and one spontaneous reaction. The active enzymes are MTA phosphorylase The methionine salvage pathway is universally used to regenerate methionine from 5¢-methylthioadenosine, a byproduct of certain reactions involving S-adenosylmethionine. We identified and verified the genes encoding the enzymes of all steps in this cycle in a commonly used eukaryotic model system: the yeast Saccharomyces cerevisiae. The genes encoding 5¢-methylthioribose-1-phosphate isomerase and 5¢-methylthioribulose-1-phosphate dehydratase are herein named MRI1 and MDE1, respectively. The 5¢-methylthioadenosine phosphorylase was verified as Meu1p, the 2,3-dioxomethiopentane-1-phosphate enolase ⁄ phosphatase as Utr4p and the aci-reductone dioxygenase as Adi1p. The homologue of the enolase ⁄ phosphatase gene, YNL010w, was excluded from its candidate role in the cycle. The methodology used involved auxotrophic growth tests and analysis of intracellular 5¢-methylthioadenosine in deletion mutants. The last step, a transamination of 4-methylthio-2-oxobutyrate to yield methionine, was found to be a highly redundant step. It was catalysed by amino acid transaminases, mainly coupled with aromatic and branched chain amino acids as amino donors, but also with proline, lysine and glutamate ⁄ glutamine. The aromatic amino acid transaminases, Aro8p and Aro9p, and the branched chain amino acid transaminases, Bat1p and Bat2p, seemed to be the main enzymes exhibiting 4-methylthio-2-oxobutyrate transaminase activity. Bat2p was found to be less specific and used proline, lysine, tyrosine and glutamate as amino donors in addition to the branched chain amino acids. Thus, for the first time, all enzymes of the methionine salvage pathway were identified in a eukaryote.Abbreviations MOB, 4-methylthio-2-oxobutyrate; MTA, 5¢-methylthioadenosine; SGD, Saccharomyces Genome Database

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Section: Discussionsupporting

confidence: 66%

A complete inventory of all enzymes in the eukaryotic methionine salvage pathway

Pirkov¹,

Norbeck²,

Gustafsson³

et al. 2008

The FEBS Journal

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“…Therefore, we presume that these three steps, dehydration, enolization and dephosphorylation, may be performed by a single enzyme in higher plants. In addition, we suppose that IDI4, the putative aspartate/tyrosine/aromatic aminotransferase induced by Fe deficiency, is a candidate enzyme for the final step of the methionine cycle (Berger et al, 2003;Heilbronn et al, 1999). It has been confirmed by Northern blot analysis that transcript levels of all the candidate genes participating in this pathway (Figure 7) were increased in Fe-deficient rice roots .…”

Section: Genes Involved In the Methionine Cycle Are Upregulated By Znmentioning

confidence: 71%

“…The expression of these genes also increased dramatically in response to Fe deficiency, with induction ratios higher than those in response to Zn deficiency. Putative aspartate/tyrosine/aromatic aminotransferase (IDI4, accession number AB206815), which has been predicted to be the enzyme that catalyze the conversion of 2-keto-4-methylthiobutyric acid (KMTB) to methionine by transamination (Berger et al, 2003;Heilbronn et al, 1999), was also upregulated by Zn deficiency and Fe deficiency. Methylthioribose (MTR) kinase was upregulated by Fe deficiency but not by Zn deficiency.…”

Section: Microarray Analysis Of Gene Expression In Barley Roots In Rementioning

confidence: 99%

Biosynthesis and secretion of mugineic acid family phytosiderophores in zinc‐deficient barley

et al. 2006

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SummaryMugineic acid family phytosiderophores (MAs) are metal chelators that are produced in graminaceous plants in response to iron (Fe) deficiency, but current evidence regarding secretion of MAs during zinc (Zn) deficiency is contradictory. Our studies using HPLC analysis showed that Zn deficiency induces the synthesis and secretion of MAs in barley plants. The levels of the HvNAS1, HvNAAT-A, HvNAAT-B, HvIDS2 and HvIDS3 transcripts, which encode the enzymes involved in the synthesis of MAs, were increased in Zn-deficient roots. Studies of the genes involved in the methionine cycle using microarray analysis showed that the transcripts of these genes were increased in both Zn-deficient and Fe-deficient barley roots, probably allowing the plant to meet its demand for methionine, a precursor in the synthesis of MAs. In addition, HvNAAT-B transcripts were detected in Zn-deficient shoots, but not in those that were deficient in Fe. Increased synthesis of MAs in Zndeficient barley was not due to a deficiency of Fe, because Zn-deficient barley accumulated more Fe than did the control plants, ferritin transcripts were increased in Zn-deficient plants, and Zn deficiency promoted Fe transport from root to shoot. Moreover, analysis using the positron-emitting tracer imaging system (PETIS) confirmed that more 62 Zn(II)-MAs than 62 Zn 2þ were absorbed by the roots of Zn-deficient barley plants. These data suggest that the increased biosynthesis and secretion of MAs arising from a shortage of Zn are not due to an induced Fe deficiency, and that secreted MAs are effective in absorbing Zn from the soil.

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“…suggesting that it is a plant TAT with multi-substrate specificity. Some microbial TATs also have a broad substrate specificity, including TATs from Klebsiella pneumoniae (Heilbronn et al, 1999), Bacillus sp. (Berger et al, 2003), and Trypanosoma cruzi (Nowickia et al, 2001), which deaminate Tyr (3) as well as other aromatic and aliphatic amino acids.…”

Section: Attat1 and Attat2 Have Distinct Substrate Specificity And Prmentioning

confidence: 99%

Biochemical properties and subcellular localization of tyrosine aminotransferases in Arabidopsis thaliana

2016

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Plants produce various L-tyrosine (Tyr)-derived compounds that are of pharmaceutical or nutritional importance to humans. Tyr aminotransferase (TAT) catalyzes the reversible transamination between Tyr and 4-hydroxyphenylpyruvate (HPP), the initial step in the biosynthesis of many Tyr-derived plant natural products. Herein reported is the biochemical characterization and subcellular localization of TAT enzymes from the model plant Arabidopsis thaliana. Phylogenetic analysis showed that Arabidopsis has at least two homologous TAT genes, At5g53970 (AtTAT1) and At5g36160 (AtTAT2). Their recombinant enzymes showed distinct biochemical properties: AtTAT1 had the highest activity towards Tyr, while AtTAT2 exhibited a broad substrate specificity for both amino and keto acid substrates. Also, AtTAT1 favored the direction of Tyr deamination to HPP, whereas AtTAT2 preferred transamination of HPP to Tyr. Subcellular localization analysis using GFP-fusion proteins and confocal microscopy showed that AtTAT1, AtTAT2, and HPP dioxygenase (HPPD), which catalyzes the subsequent step of TAT, are localized in the cytosol, unlike plastid-localized Tyr and tocopherol biosynthetic enzymes. Furthermore, subcellular fractionation indicated that, while HPPD activity is restricted to the cytosol, TAT activity is detected in both cytosolic and plastidic fractions of Arabidopsis leaf tissue, suggesting that an unknown aminotransferase(s) having TAT activity is also present in the plastids. Biochemical and cellular analyses of Arabidopsis TATs provide a fundamental basis for future in vivo studies and metabolic engineering for enhanced production of Tyr-derived phytochemicals in plants.

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Tyrosine Aminotransferase Catalyzes the Final Step of Methionine Recycling in Klebsiella pneumoniae

Cited by 38 publications

References 50 publications

A complete inventory of all enzymes in the eukaryotic methionine salvage pathway

A complete inventory of all enzymes in the eukaryotic methionine salvage pathway

Biosynthesis and secretion of mugineic acid family phytosiderophores in zinc‐deficient barley

Biochemical properties and subcellular localization of tyrosine aminotransferases in Arabidopsis thaliana

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