Characterization of cobalamin-dependent methionine synthase purified from the human malarial parasite, Plasmodium falciparum

Abstract

Methionine synthase, which catalyzes the reaction, 5-methyltetrahydrofolate (5-CH 3 -H 4 PteGlu)+homocysteine→methionine+tetrahydrofolate, was detected and partially purified from the human malarial parasite, Plasmodium falciparum (K 1 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 105000 daltons, and the apparent K m for 5-CH 3 -H 4 PteGlu was 24.2 μM. 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-CH 3 -H 4 PteGlu for tetrahydrofolate metabolism. © 1989 Springer-Verlag.