Samples were prepared in 100 mM aqueous potassium phosphate buffer, pH 7.4, 0.05 % lauryl maltoside, 22°C, 1.00 cm pathlengths. Broken trace: partially-reduced cyanide adduct, 12 μM in enzyme, 0.2 mM in KCN, ~1 mM in Na2S2O4; dotted trace: partially-reduced cyanide adduct plus CO, 12 μM in enzyme, 0.2 mM in KCN, ~1 mM in Na2S2O4, ~1 mM (1.0 atm) CO; solid trace: partially-reduced cyanide adduct plus NO, 12 μM in enzyme, 0.2 mM in KCN, ~1 mM in Na2S2O4, 1.9 mM (1.0 atm) NO.