Spectroscopic study of the cobalamin-dependent methionine synthase in the activation conformation: effects of the Y1139 residue and S-adenosylmethionine on the B12 cofactor.

ABSTRACT: The cobalamin-dependent methionine synthase (MetH) from Escherichia coli is a modular enzyme that catalyzes a methyl group transfer from methyltetrahydrofolate to homocysteine via a methylcob(III)alamin (MeCbl) intermediate, generating tetrahydrofolate and methionine (Met). Once every approximately 2000 turnovers, the cobalamin cofactor is converted to the inactive cob(II)alamin (Co(2+)Cbl) form, from which MeCbl has to be recovered for MetH to re-enter the catalytic cycle. A particularly puzzling aspect of this reactivation process is that it requires the reduction of the Co(2+)Cbl species to cob(I)alamin (Co(1+)Cbl) by flavodoxin, a reaction that would appear to be endergonic on the basis of the corresponding reduction potentials. To explore how MetH may overcome this apparent thermodyna

SUBMITTER: Liptak MD 

PROVIDER: S-EPMC3101771 | biostudies-literature | 2008 Dec

REPOSITORIES: biostudies-literature