title: Characterization of cobalamin-dependent methionine synthase purified from the human malarial parasite, Plasmodium falciparum.
abstract: Methionine synthase, which catalyzes the reaction, 5-methyltetrahydrofolate (5-CH3-H4PteGlu) + homocysteine----methionine + tetrahydrofolate, was detected and partially purified from the human malarial parasite, Plasmodium falciparum (K1 isolate). Partial purification was achieved using high-performance size-exclusion and anion-exchange chromatography. The apparent relative molecular weight of the enzyme was estimated as 105,000 daltons, and the apparent Km for 5-CH3-H4PteGlu was 24.2 microM. The enzyme was dependent on adenosylcobalamin or methylcobalamin but not on cobalamin, cyanocobalamin, or hydroxocobalamin in either the absence or presence of S-adenosylmethionine. Preincubation with nitrous oxide markedly inhibited the enzyme. Methionine synthase in P. falciparum may play a role in the supply of methionine and in folate salvage using exogenous 5-CH3-H4PteGlu for tetrahydrofolate metabolism.
authors.affiliation: Department of Biochemistry, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand.
authors.forename: J
authors.initials: J
authors.lastname: Krungkrai
authors.forename: H K
authors.initials: HK
authors.lastname: Webster
authors.forename: Y
authors.initials: Y
authors.lastname: Yuthavong
mesh_terms: D013766:5-Methyltetrahydrofolate-Homocysteine S-Methyltransferase / Q000032:analysis / Q000302:isolation & purification*; D000818:Animals; D002850:Chromatography, Gel; D002852:Chromatography, Ion Exchange; D006801:Humans; D008780:Methyltransferases / Q000302:isolation & purification*; D008970:Molecular Weight; D010963:Plasmodium falciparum / Q000201:enzymology* / Q000254:growth & development; D014805:Vitamin B 12 / Q000378:metabolism*
chemical_list: D008780:Methyltransferases; D013766:5-Methyltetrahydrofolate-Homocysteine S-Methyltransferase; D014805:Vitamin B 12