Co(II)/Co(I) reduction-induced axial histidine-flipping in myoglobin reconstituted with a cobalt tetradehydrocorrin as a methionine synthase model

A conjugate between apomyoglobin and cobalt tetradehydrocorrin was prepared to replicate the coordination behavior of cob(I) alamin in methionine synthase. X-ray crystallography reveals that the tetra-coordinated Co(I) species is formed through the cleavage of the axial Co-His93 ligation after the reduction of the penta-coordinated Co(II) cofactor in the heme pocket.