Two enzymic mechanisms for the methylation of homocysteine by extracts of <i>Escherichia coli</i>

Foster, M. A.; Tejerina, G.; Guest, J. R.; Woods, D. D.

doi:10.1042/bj0920476

Cited by 69 publications

(57 citation statements)

References 21 publications

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“…The orientation of the polar effects is consistent with the direction of transcription of the eut operon (from left to right in Fig. 3 and 4) which was determined previously by using eut-lac operon fusions (27 (16). The function of the B12-dependent enzyme…”

Section: Methodssupporting

confidence: 57%

“…A B12-dependent methyl transferase (encoded by the metH gene) methylates homocysteine to form methionine (35). The metH enzyme is not essential for methionine biosynthesis because a B12-independent enzyme (encoded by the metE gene) can catalyze the same reaction (16). Vitamin B12 is also required for formation of the modified base queuosine present in the anticodon loop of some tRNAs, but this modification is not essential under standard growth conditions (18).…”

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confidence: 99%

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Functions required for vitamin B12-dependent ethanolamine utilization in Salmonella typhimurium

1989

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When B12 is available, Salmonella typhimurium can degrade ethanolamine to provide a source of carbon and nitrogen. B12 is essential since it is a cofactor for ethanolamine ammonia-lyase, the first enzyme in ethanolamine breakdown. S. typhimurium makes B12 only under anaerobic conditions; in the presence of oxygen, exogenous B12 must be provided to permit ethanolamine utilization. Genes required for ethanolamine utilization are encoded in the eut operon generally provided in laboratory media, neither form of B12 can be used directly as the cofactor for ethanolamine ammonia-lyase. To form Ado-B12 from exogenous B12, the cell must transport the B12, reduce the central cobalt atom, and add an adenosyl group (Fig. 1) (20). A high-affinity B12 transport system has been described for Escherichia coli (13); a similar system appears to exist in S. typhimurium.The enzymes responsible for reduction and adenosylation have been studied in several species of bacteria (5,31,33 (27). Induction of transcription of the eut operon requires the simultaneous presence of ethanolamine and B12, but the mechanism by which this regulation pattern 3316

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Section: Methodssupporting

confidence: 57%

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confidence: 99%

Functions required for vitamin B12-dependent ethanolamine utilization in Salmonella typhimurium

1989

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“…It has been shown ( Table 3) that extracts of Escherichia coli 26/18 lack cystathionase whilst it was known that extracts of strain 1211176 lack homocysteine methylase activity (i.e. ability to convert homocysteine to methionine) unless cobalamin is present (Guest et al 1960;Foster, Tejerina & Woods, 1961). Neither extract alone converted cystathionine to methionine, but a mixture of the two was effective (Table 4), thus confirming the view that methionine formation from cystathionine requires the successive action of cystathionase and homocysteine methylase, and that in this particular case each organism provides the enzyme or enzymes lacking in the other.…”

Section: Cystathionase Activity Of Various Strains Of Escherichia Colimentioning

confidence: 99%

“…The final reaction by which homocysteine is converted to methionine is a complicated one requiring folic acid derivatives and, in certain circumstances, also cobalamin as cofactors (Guest & Woods, 1962). However, the formation of the enzyme complex (homocysteine methylase), and indeed individual components of it, is repressed by the presence of methionine in the culture medium; the enzymes are, however, rapidly resynthesized when methionine is removed (Rowbury & Woods, 1961 ;Foster, Rowbury & Woods, 1963). The main objective of the present work was to examine the effect of growth with methionine on the cystathionase content of E. coli with conditions under which it could be strictly compared with the known effect on the homoc ys t eine met hy lase complex.…”

Section: Introductionmentioning

confidence: 99%

Repression by Methionine of Cystathionase Formation in Escherichia coli

Rowbury

Woods

1964

Journal of General Microbiology

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SUMMARYCystathionase catalyses the formation of homocysteine from cystathionine; its formation in cultures of Escherichia coli is repressed by the presence of methionine in the growth medium, and to a similar extent to that shown with homocysteine methylase (the enzyme complex which catalyses the conversion homocysteine -+ methionine). Cystathionase, again like homocysteine methylase, is formed rapidly without concomitant growth when repressed organisms are transferred to a medium free from methionine ; such enzyme formation is prevented by chloramphenicol, suggesting that de novo synthesis of protein is required. The co-repression by methionine of the two enzyme systems fortifies the evidence that cystathionase is a component of the normal pathway of methionine synthesis by E . coli and consequently that its substrate, cystathionine, is a normal intermediate. Cystathionase preparations also formed pyruvate from cysteine; this activity paralleled that of cystathionase itself when the methionine status of the medium was changed, and it is concluded that the same protein is responsible for both activities. INTRODUCTIONIn previous work in this laboratory Wijesundera & Woods (1962) showed that L-cystathionine was converted to homocysteine, pyruvate and ammonia by a cystathionase enzyme present in several strains of Escherichia coli. Since homocysteine is undoubtedly the immediate precursor of methionine in this organism (see review by Guest & Woods, 1962), these observations supported the view, originating from the properties of methionine auxotrophs of 23. coli and other micro-organisms, that cystathionine is an earlier intermediate, though there remained some evidence to the contrary (see Discussion). The final reaction by which homocysteine is converted to methionine is a complicated one requiring folic acid derivatives and, in certain circumstances, also cobalamin as cofactors (Guest & Woods, 1962). However, the formation of the enzyme complex (homocysteine methylase), and indeed individual components of it, is repressed by the presence of methionine in the culture medium; the enzymes are, however, rapidly resynthesized when methionine is removed (Rowbury & Woods, 1961 ; Foster, Rowbury & Woods, 1963). The main objective of the present work was to examine the effect of growth with methionine on the cystathionase content of E. coli with conditions under which it could be strictly compared with the known effect on the homoc ys t eine met hy lase complex. TO Xhcrob. xxxvDownloaded from www.microbiologyresearch.org by

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“…B12-dependent transferase (metH) is not essential since, in the absence of B12, an alternative transferase (metE) is capable of synthesizing methionine without B12 (19). Thus, neither of the B12-dependent functions is essential under most growth conditions.…”

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Ethanolamine utilization in Salmonella typhimurium

1988

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Ethanolamine can serve as the sole source of carbon and nitrogen for Salmonella typhimurium if vitamin B,2 is present to serve as a cofactor. The pathway for ethanolamine utilization has been investigated in order to understand its regulation and determine whether the pathway is important to the selective forces that have maintained the ability to synthesize B12 in S. typhimurium. We isolated mutants that are defective in ethanolamine utilization (eut mutants). These mutants defined a cluster of genes located between purC and cysA at 50 min on the Salmonella chromosome. A genetic map of the eut region was constructed. Included in the map are mutations which affect ethanolamine ammonia lyase, the first degradative enzyme, and mutations which affect the second enzyme in the pathway, acetaldehyde dehydrogenase. Transcriptional regulation of the eat genes was studied by using eut-lac operon fusions created by insertion of Mu d lac. Transcription is induced by the simultaneous presence of ethanolamine and B12 in the growth medium. The eut genes constitute a single unit of transcription. One class of mutations located at the promoter-distal end of the eut operon prevent induction of transcription.

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Two enzymic mechanisms for the methylation of homocysteine by extracts of Escherichia coli

Cited by 69 publications

References 21 publications

Functions required for vitamin B12-dependent ethanolamine utilization in Salmonella typhimurium

Functions required for vitamin B12-dependent ethanolamine utilization in Salmonella typhimurium

Repression by Methionine of Cystathionase Formation in Escherichia coli

Ethanolamine utilization in Salmonella typhimurium

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