FIGURE 6.

Kinetics of the reaction of a pre-mixed solution of MCR_red1 (18 μm) and CoB₇SH (18 μm) with methyl-SCoM at concentrations of 0.125, 0.25, 0.5, 1, and 2 mm (final concentrations) in 50 mm Tris-HCl pH 7.6. The reactions were performed under anaerobic conditions using the stopped-flow spectrophotometer at 25 °C and monitored at 385 (A) and 420 nm (B). The traces were fit to a single exponential equation. The dashed lines represent simulations based on the model presented in Scheme 2 with kinetic parameters listed in Table 1 and the following extinction coefficients: ϵ₃₈₅(MCR(Ni^I)) = 37,340 m⁻¹ cm⁻¹; ϵ₃₈₅(MCR(Ni^I)·CH₃SCoM) = 35,040 m⁻¹ cm⁻¹; ϵ₃₈₅(CoB₇SH·MCR(Ni^I)·CH₃SCoM) = 30,010 m⁻¹ cm⁻¹; ϵ₃₈₅(MCR(Ni^II)·CoB₇S⁻·SCoM) = 25,490 m⁻¹ cm⁻¹; ϵ₃₈₅(MCR(Ni^I)·CoB₇SH) = 35,790 m⁻¹ cm⁻¹; ϵ₃₈₅(CoB₇SH·MCR(Ni^I)·CH₃SCoM*) = 35,550 m⁻¹ cm⁻¹; ϵ₄₂₀(MCR(Ni^I)) = 18,060 m⁻¹ cm⁻¹; ϵ₄₂₀(MCR(Ni^I)·CH₃SCoM) = 20,620 m⁻¹ cm⁻¹; ϵ₄₂₀(CoB₇SH·MCR(Ni^I)·CH₃SCoM) = 20,550 m⁻¹ cm⁻¹; and ϵ₄₂₀(MCR(Ni^II)·CoB₇S⁻·SCoM) = 20,100 m⁻¹ cm⁻¹; ϵ₄₂₀(MCR(Ni^I)·CoB₇SH) = 21,070 m⁻¹ cm⁻¹; and ϵ₄₂₀(CoB₇SH·MCR(Ni^I)·CH₃SCoM*) = 22,920 m⁻¹ cm⁻¹.