Catalase native system

The autoxidation of ascorbate, a cosubstrate of dopamine P-monooxygenase, induces the degradation of most proteins including catalase and dopamine p-monooxygenase, but with the exception of (Cu,Zn)-SOD. Catalase protects dopamine P-monooxy-genase and is therefore generally added in the assay systems . The apparent activation or rather the stabilization of the enzyme (6.5 pg) by small amounts of catalase (3.1 pg) was enhanced by native but not by boiled SOD (100 pg) and also by similar amounts of serumalbumin (100 pg) or of boiled catalase (65 pg)... 

However, the activity of a heme(in) protein towards hydroperoxides is influenced by its steric accessibility to fatty acid hydroperoxides. Hydroperoxide binding to the Fe-porphyrin moiety of native catalase and peroxidase molecules is obviously not without interferences. The prosthetic group is free to promote hydroperoxide decomposition only after heat denaturation of the enzymes. Indeed, a model experiment with peroxidase showed that the peroxidation of linoleic acid increased by a factor of 10 when the enzyme was heated for 1 minute to 140 °C. As expected, the enzymatic activity of peroxidase decreased and was only 14%. Similar results were obtained in reaction systems containing catalase. 

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