Figure 4.

Time course of the oxidation of reduced ba₃ by NO. ba₃ (5 μM) was reduced anaerobically by 1 mM ascorbate in the presence of 1 mM CO, and the resulting CO-bound fully reduced enzyme was mixed with 250 μM NO at 20°C. (Upper) Absorption changes collected from 10 ms to 80 s after mixing. (Lower) Optical components deconvoluted by fitting the first two V columns of the singular value decomposition output (scaled by their relative singular values) to two exponential decays (Inset: best fit). The faster phase (solid spectrum) corresponds to CO displacement by NO, proceeding at k₁ = 9 s⁻¹, whereas cytochrome b oxidation (dashed spectrum) occurs at a much slower rate, k₂ = 0.04 s⁻¹, which is consistent with the turnover number measured for NO consumption by ba₃.