Catalase Activity

C), there is a broad range of temperature-induced decreases in enzyme activity. Catalase is seen as the most thermally stable enzyme in this group, while creatine phosphokinase (or CPK) is the most thermally sensitive enzyme. 

This enzyme occurs in plants, animals, and microorganisms. The molecule has four subunits each of these contains a protohemin group, which forms part of four independent active sites. The molecular weight is 240,000. Catalase is less stable to heat than is peroxidase. At neutral pH, catalase will rapidly lose activity at 35°C. In addition to catalyzing the reaction shown above (catalatic activity), catalase can also have peroxidatic... 

Regbnbration op Active Catalase from the Cvanylated Enzyme, 25 ... 

Some of these enzyme-substrate complexes, in a second reaction sequence, can oxidize a hydrogen donor molecule. If this donor happens to be HiOs we speak of catalatic activity, and if other hydrogen donors are oxidized, of peroxidatic activity. Catalase can exhibit both activities, whereas peroxidase can act only peroxidatically. 

Chance (86) had previously demonstrated the existence of an active catalase-H2O2 complex, now called complex I, and in 1951 Keilin and Hartree (7) found a third, also inactive complex III, formed from complex II at higher Ht02 concentrations. 

Fig. 7A. The principle of the two-mixer method (24) for measuring over-all catalase activity. Catalase and hydrogen peroxide are rapidly mixed and the reaction is quenched by sulfuric acid after a time interval of 0.2 second. The residual HjO, is subsequently titrated with permanganate (FA-19).

Effitiency of the Enzsrme Mechanism.—A highly active catalase has been prepared from horse liver by Zeile and Hellstrbm, and shown to be an iron porphyran with a spectrum resembling alkaline haematin. Haldane has calculated that at 0° C. one molecule of this enzyme catalyses the decomposition of about 2 X 10 molecules per second. 

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