Interaction of met-Hb with HOCl leads to the transient formation of Compound II, prior to heme destruction. Absorbance spectra recorded by diode array stopped-flow when a phosphate buffer solution (0.20 M, pH 7.0) containing 1.25 µM met-Hb was rapidly mixed with a buffer solution containing 400 µM HOCl, at 10°C. The upper panel contains spectra collected after 0.05, 0.15, 0.25, 0.95 and 1.5 s of initiating the reaction, which shows the accumulation of compound II. The inset in upper panel shows the accumulation of Compound II as judged by the transition of the Soret absorbance peak from 405 nm to 420 nm. The lower panel contains spectra collected after 1.5, 9.5, 34.5, 89.5, 149.5, 599.5 s of initiating the reaction, which shows Compound II heme destruction. Arrows indicate the direction of spectral change over time. The experiment shown is representative of three.