Properties of catalase. Catalysis of coupled oxidation of alcohols

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Abstract
Certain oxidizing enzymes, in catalyzing the oxidation of their substrates by molecular O2, reduced the latter to H2O2, which in the presence of catalase was decomposed 2H2O2 = H2O + O2 (1). Pure catalase alternately utilized the H2O2 formed in the primary reaction for catalysis of secondary or coupled oxidation of alcohols to aldehydes: RCH2OH + H2O2 = RCHO + 2H2O (2). For catalysis of this coupled oxidation (2), H2O2 formed in the primary oxidation was replaced by H2O2 resulting from slow decomposition of Ba or Ce peroxides, or by free H2O2 provided the concn. of the latter was kept low by gradual addition. Every molecule of H2O2 derived from primary oxidation was used in reaction (2) but in all other forms of addition of H2O2, reaction (1) predominated. In presence of xanthine oxidase and aldehyde, catalase also promoted a cyclic oxidation of ethanol to acetic acid until all alcohol was oxidized. In a system of d-amino-acid oxidase and alanine, the H2O2 formed was utilized in a non-catalyzed coupled oxidation of pyruvate to acetate and CO2. If catalase and ethanol were added to this system, H2O2 was utilized for the coupled oxidation of the ethanol, leaving the pyruvate unattached. The high endo-erythrocytic catalase did not protect the divalent Fe of Hb from oxidation by H2O2 formed in a primary oxidation system. The presence of catalase in microorganisms did not protect them from the toxic effect of H2O2 either added or formed in the medium by oxidation reactions. The main function of catalase was the catalysis of coupled oxidation by means of H2O2 formed in the primary oxidation, and not to protect cells from the toxic action of H2O2 by decomposing it to H2O and O2. The concn. of catalase in liver tissues was 1000 times higher than required for catalytic decomposition of H2O2, and was of the same order as was necessary for catalysis of coupled oxidation (2). Only methanol, ethanol, n-propanol, isobutanol, [beta]-aminoethanol and ethylene glycol underwent coupled oxidation catalyzed by catalase in vitro.