Catalase: kinetics of photooxidation.

The kinetics of photooxidation of catalase is a four-step consecutive reaction, if each of the four porphyrin moieties acts independently. The rate of enzyme inactivation is a first-order reaction resulting from destruction of a single porphyrin. The kinetics of absorbancy is more complex, depending upon the absorption probabilities of each of the microspecies. With equal probabilities. the log of the sum of the normalized absorptivities is a linear function of time.