The optical absorption spectrum of bovine liver catalase was found to change on light irradiation in the presence of proflavin and EDTA in a deaerated solution. Upon addition of CO to the photolyzed product, the spectrum changed to an another form, suggesting that the photolyzed product is the ferrous form of the enzyme and CO is bound to the ferrous enzyme. When 02was introduced into the ferrous enzyme, the absorption spectrum returned to its original ferric state. An intermediate spectrum was obtained in this reaction at−20°C in 33v/v ethylene glycol. Judged from the spectral characteristics of this compound, it is probablyan oxyferrous enzyme. It was converted into ferric enzyme gradually when the sample was left at room temperature. The ferrous enzyme, which was generated by flash photolysis of the CO complex of the enzyme in an air-saturated buffer, reacted with O2to form the oxyferrous enzyme with a second order rate constant of 9.2×103M−1s−1at pH 8.6 and 20°C. The oxyferrous enzyme thus obtained autodecomposed into the ferric form with a rate constant of
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