FIGURE 4.

Reaction between wild-type mALAS2 (30 μm) and ALA (10 mm). A, progress curve for the formation of the ALA-mALAS2 external aldimine as monitored at 420 nm. The data points were fit to a two-exponential equation yielding the observed rate constants (k₁ and k₂) and amplitudes (A₁ and A₂): k₁ = 4.7 ± 0.01 s⁻¹ and A₁ = 1.1 × 10⁻³ ± 0.07 × 10⁻³ for the fast phase, and k₂ = 0.37 ± 0.003 s⁻¹ and A₂ = 5.2 × 10⁻³ ± 0.02 × 10⁻³ for the slow phase. The inset shows the first 2.5 s of the reaction. B, progress curve for the formation of the ALA quinonoid intermediate as monitored at 510 nm. The observed rate constants (k₁ and k₂) and amplitudes (A) were: k₁ = 0.61 ± 0.01 s⁻¹ and A₁ = 4.50 × 10⁻³ ± 0.07 × 10⁻³ for the fast phase, and k₂ = 0.08 ± 0.01 s⁻¹ and A₂ = 1.50 × 10⁻³ ± 0.04 × 10⁻³ for the slow phase.