Biosynthesis of Mustard Oil Glucosides: Iv. The Administration of Methionine-C14 and Related Compounds to Horseradish

Chisholm, M. D.; Wetter, L. R.

doi:10.1139/o64-114

Cited by 47 publications

(15 citation statements)

References 7 publications

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“…1). Early feeding experiments with radiolabeled amino acids and acetate (Chisholm and Wetter 1964;Serif 1968, 1970) suggested an outline for the pathway. This was confirmed by more detailed in vivo studies with stableisotope-labeled tracers (Graser et al 2000) and by isolation of a key intermediate (Chapple et al 1988).…”

Section: Introductionmentioning

confidence: 99%

Biosynthesis of methionine-derived glucosinolates in Arabidopsis thaliana : recombinant expression and characterization of methylthioalkylmalate synthase, the condensing enzyme of the chain-elongation cycle

Textor

Bartram

Kroymann

et al. 2004

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The major class of glucosinolates in Arabidopsis thaliana (L.) Heynh. are biosynthesized from methionine involving a three-step chain-elongation cycle. Each passage through the cycle results in the net addition of a single methylene group, with up to six cycles of elongation occurring in A. thaliana. The first reaction of the cycle is catalyzed by a methylthioalkylmalate synthase (MAMS), which condenses a omega-methylthio-2-oxoalkanoic acid with acetyl-CoA. Here we have demonstrated that MAM1, one of two similar genes in the A. thaliana ecotype Columbia, encodes a MAMS catalyzing the condensing reactions of the first two elongation cycles but not those of further cycles. The Columbia ecotype is dominated by compounds that have undergone only two elongation cycles. The A. thaliana MAM1 protein exhibits basic sequence similarity to other previously described enzymes catalyzing the condensation of 2-oxo acids and acetyl-CoA, such as isopropylmalate synthase (EC 2.3.3.13), an enzyme of leucine biosynthesis, and homocitrate synthase (EC 2.3.3.14). It also shares similar properties with them, including the catalytic requirements for a divalent metal ion and an adenine nucleotide. However, the MAM1 protein does not show activity with the substrates of any of these other enzymes, and was chromatographically separable from isopropylmalate synthase in extracts of A. thaliana. Thus, MAM1 is exclusively an enzyme of secondary metabolism, distinct from primary metabolic enzymes catalyzing similar reactions.

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Section: Introductionmentioning

confidence: 99%

Biosynthesis of methionine-derived glucosinolates in Arabidopsis thaliana : recombinant expression and characterization of methylthioalkylmalate synthase, the condensing enzyme of the chain-elongation cycle

Textor

Bartram

Kroymann

et al. 2004

Planta

111

129

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“…Glucosinolates of six different chain lengths are produced in Arabidopsis. Studies with labeled Met and acetate have shown that elongation of the Met side chain involves a repetitive cycle of three reaction steps that result in the net addition of one methylene carbon for each turn of the cycle (Chisholm and Wetter, 1964;Serif, 1968, 1970;Graser et al, 2000). To enter the cycle, Met is first deaminated to the corresponding 2-oxo-acid, 4-methylthio-2-oxobutanoic acid.…”

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confidence: 99%

MAM3 Catalyzes the Formation of All Aliphatic Glucosinolate Chain Lengths in Arabidopsis

et al. 2007

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Chain elongated, methionine (Met)-derived glucosinolates are a major class of secondary metabolites in Arabidopsis (Arabidopsis thaliana). The key enzymatic step in determining the length of the chain is the condensation of acetyl-coenzyme A with a series of v-methylthio-2-oxoalkanoic acids, catalyzed by methylthioalkylmalate (MAM) synthases. The existence of two MAM synthases has been previously reported in the Arabidopsis ecotype Columbia: MAM1 and MAM3 (formerly known as MAM-L). Here, we describe the biochemical properties of the MAM3 enzyme, which is able to catalyze all six condensation reactions of Met chain elongation that occur in Arabidopsis. Underlining its broad substrate specificity, MAM3 also accepts a range of non-Met-derived 2-oxoacids, e.g. converting pyruvate to citramalate and 2-oxoisovalerate to isopropylmalate, a step in leucine biosynthesis. To investigate its role in vivo, we identified plant lines with mutations in MAM3 that resulted in a complete lack or greatly reduced levels of long-chain glucosinolates. This phenotype could be complemented by reintroduction of a MAM3 expression construct. Analysis of MAM3 mutants demonstrated that MAM3 catalyzes the formation of all glucosinolate chain lengths in vivo as well as in vitro, making this enzyme the major generator of glucosinolate chain length diversity in the plant. The localization of MAM3 in the chloroplast suggests that this organelle is the site of Met chain elongation.

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“…2) that convert 2-oxoisovalerate into Leu ( Fig. 1; Chisholm and Wetter, 1964;Matsuo and Yamazaki, 1968;Serif and Schmotzer, 1968;Graser et al, 2000). Each cycle of elongation is initiated by an aldol-type condensation between acetyl-CoA and a v-methylthio-2-oxo acid leading to the formation of a v-methylthioalkylmalate.…”

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Two Arabidopsis Genes (IPMS1 and IPMS2) Encode Isopropylmalate Synthase, the Branchpoint Step in the Biosynthesis of Leucine

et al. 2006

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Heterologous expression of the Arabidopsis (Arabidopsis thaliana) IPMS1 (At1g18500) and IPMS2 (At1g74040) cDNAs in Escherichia coli yields isopropylmalate synthases (IPMSs; EC 2.3.3.13). These enzymes catalyze the first dedicated step in leucine (Leu) biosynthesis, an aldol-type condensation of acetyl-coenzyme A (CoA) and 2-oxoisovalerate yielding isopropylmalate. Most biochemical properties of IPMS1 and IPMS2 are similar: broad pH optimum around pH 8.5, Mg 21 as cofactor, feedback inhibition by Leu, K m for 2-oxoisovalerate of approximately 300 mM, and a V max of approximately 2 3 10 3 mmol min 21 g 21 . However, IPMS1 and IPMS2 differ in their K m for acetyl-CoA (45 mM and 16 mM, respectively) and apparent quaternary structure (dimer and tetramer, respectively). A knockout insertion mutant for IPMS1 showed an increase in valine content but no changes in Leu content; two insertion mutants for IPMS2 did not show any changes in soluble amino acid content. Apparently, in planta each gene can adequately compensate for the absence of the other, consistent with available microarray and reverse transcription-polymerase chain reaction data that show that both genes are expressed in all organs at all developmental stages. Both encoded proteins accept 2-oxo acid substrates in vitro ranging in length from glyoxylate to 2-oxohexanoate, and catalyze at a low rate the condensation of acetyl-CoA and 4-methylthio-2-oxobutyrate, i.e. a reaction involved in glucosinolate chain elongation normally catalyzed by methylthioalkylmalate synthases. The evolutionary relationship between IPMS and methylthioalkylmalate synthase enzymes is discussed in view of their amino acid sequence identity (60%) and overlap in substrate specificity.

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Biosynthesis of Mustard Oil Glucosides: Iv. The Administration of Methionine-C14 and Related Compounds to Horseradish

Cited by 47 publications

References 7 publications

Biosynthesis of methionine-derived glucosinolates in Arabidopsis thaliana : recombinant expression and characterization of methylthioalkylmalate synthase, the condensing enzyme of the chain-elongation cycle

Biosynthesis of methionine-derived glucosinolates in Arabidopsis thaliana : recombinant expression and characterization of methylthioalkylmalate synthase, the condensing enzyme of the chain-elongation cycle

MAM3 Catalyzes the Formation of All Aliphatic Glucosinolate Chain Lengths in Arabidopsis

Two Arabidopsis Genes (IPMS1 and IPMS2) Encode Isopropylmalate Synthase, the Branchpoint Step in the Biosynthesis of Leucine

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