FIG 4.
MtpA does not catalyze cob(I)alamin methylation using methyl-CoM, DMS, MeOH, or DMA. Methylation of cob(I)alamin monitored via UV-visible spectroscopy using a variety of potential methyl donors. Formation of methyl-cob(III)alamin would result in an increase in absorbance at 540 nm, as seen in Fig. 3, as opposed to the slight loss of absorbance, presumably caused by photobleaching, seen in these assays (indicated by arrows). (A) Spectra gathered of cob(I)alamin with 40 mM CH3-CoM at 30-min intervals for 10 h after the start of reaction. (B) Spectra gathered of cob(I)alamin with 40 mM DMS at 2-min intervals from 0 min to 40 min after the start of reaction. (C) Spectra gathered of cob(I)alamin with 40 mM MeOH at 2-min intervals from 0 min to 40 min after the start of reaction. (D) Spectra gathered of cob(I)alamin with 40 mM DMA at 2-min intervals from 0 min to 40 min after the start of reaction.