FIGURE 6.

Reductive activation of MV8465 by MV10335. In order for methylotrophic methanogenesis pathways to function, the corrinoid binding protein must be in the active Co(I) state. MV10335 functions to reduce MV8465 to this active state. Ti(III)-citrate serves as an electron source for MV10335 but can also reduce MV8465 to Co(II), and therefore was added prior to the addition of MV10335. (A) Each spectrum is a time point with the black arrows indicating an increase absorbance at 378 nm and a decrease in absorbance at 478 nm, which is characteristic of reduction from Co(II) to Co(I). (B) MV8465 was initially reduced to Co(II) by Ti(III)-citrate to a stabilized spectrum (black line) and was then reduced to a Co(I) by the addition of MV10335 (red line). The major peak seen at 386 nm is characteristic of a Co(I) species. Addition of MV8460 and GB resulted in a decrease at 386 nm and an increase at 540 nm (blue line) indicating the formation of methylcob(III)alamin.