Properties of the methylcobalamin:H4folate methyltransferase involved in chloromethane utilization by Methylobacterium sp. strain CM4
| Autor: | Stéphane Vuilleumier, Alex Studer, Thomas Leisinger |
|---|---|
| Rok vydání: | 1999 |
| Předmět: |
Methyltransferase
Stereochemistry Molecular Sequence Data Biochemistry Catalysis Cofactor chemistry.chemical_compound medicine Amino Acid Sequence DNA Primers chemistry.chemical_classification Base Sequence Gram-Negative Aerobic Bacteria Sequence Homology Amino Acid biology Chloromethane Temperature Tetrahydromethanopterin Hydrogen-Ion Concentration Chromatography Ion Exchange Protein O-Methyltransferase biology.organism_classification Recombinant Proteins Enzyme chemistry Methylcobalamin Methyl Chloride biology.protein Methylobacterium Electrophoresis Polyacrylamide Gel Energy source medicine.drug |
| Zdroj: | European Journal of Biochemistry. 264:242-249 |
| ISSN: | 1432-1033 0014-2956 4615-4620 |
| DOI: | 10.1046/j.1432-1327.1999.00629.x |
| Popis: | Methylobacterium sp. strain CM4 is a strictly aerobic methylotrophic proteobacterium growing with chloromethane as the sole carbon and energy source. Genetic evidence and measurements of enzyme activity in cell-free extracts have suggested a multistep pathway for the conversion of chloromethane to formate. The postulated pathway is initiated by a corrinoid-dependent methyltransferase system involving methyltransferase I (CmuA) and methyltransferase II (CmuB), which transfer the methyl group of chloromethane onto tetrahydrofolate (H4folate) [Vannelli et al. (1999) Proc. Natl Acad. Sci. USA 96, 4615-4620]. We report the overexpression in Escherichia coli and the purification to apparent homogeneity of methyltransferase II. This homodimeric enzyme, with a subunit molecular mass of 33 kDa, catalyzed the conversion of methylcobalamin and H4folate to cob(I)alamin and methyl-H4folate with a specific activity of 22 nmol x min-1 x (mg protein)-1. The apparent kinetic constants for H4folate were: Km = 240 microM, Vmax = 28.5 nmol x min-1 x (mg protein)-1. The reaction appeared to be first order with respect to methylcobalamin at concentrations up to 2 mM, presumably reflecting the fact that methylcobalamin is an artificial substitute for the methylated methyltransferase I, the natural substrate of the enzyme. Tetrahydromethanopterin, a coenzyme also present in Methylobacterium, did not serve as a methyl group acceptor for methyltransferase II. Purified methyltransferase II restored chloromethane dehalogenation by a cell free extract of a strain CM4 mutant defective in methyltransferase II. |
| Databáze: | OpenAIRE |
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