Abstract
The inhibitory effects of aliphatic and aromatic carboxylic acids (formic, acetic, propionic, butyric, benzoic, and salicylic acids) on catalase at pH 7.0 were studied by measuring the catalatic activity as a function of reagent concentration, and the results were correlated with the data obtained simultaneously by spectroscopic and ultracentrifugal analyses. The inhibition by salicylic and benzoic acids proceeds in two steps. In the first step, the activity drops to a certain level, and the sedimentation peak of the native catalase is unaltered. The second step of inhibition is accompanied by the dissociation of the catalase molecule into subunits, and the absorption spectrum is changed greatly. The inhibition by the aliphatic carboxylic acids except formic acid proceeds also in two steps in which the second step of inhibition is accompanied by the association of the catalase molecules. The inhibition by formic acid obeys the mechanism of the combination between heme and the free acid rather than its anion. These different types of inhibitions at neutral pH are discussed in relation to the data obtained previously at acidic pH's.
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