FIGURE 2.

Free dihydroflavins drive the conversion of 4-coordinate cob(II)alamin bound to PduO-type ACA enzymes to AdoCbl. A, spectral changes associated with the enzymatic conversion of cob(II)alamin by hATR. Arrows and increasing darkness in the spectra represent successive time points after the reaction was initiated by addition of hATR (light gray, 1 min; black, 10 min). B, spectral changes associated with photolysis of AdoCbl. The presence of AdoCbl was confirmed by exposing the product of reaction mixture from A (black) under a tungsten lamp for 10 min in an anoxic cuvette (dotted line). C, presence of AdoCbl in reaction mixture A was confirmed by bioassay using an AdoCbl auxotroph strain of S. enterica (JE7180).