STUDIES ON THE CATALASE OF A THERMOPHILIC BACTERIUM

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1. From a lysate of a themophilic bacterium a cell-free solution was prepared, which contained a thermophilic catalase together with a certain factor(s) having a specific suppressing effect upon the catalase at lower temperatures. The catalase could be freed from the suppressing factor (S-factor) by charcoal-treatment of the solution, and the S-factor free from the enzyme was obtained by boiling the same solution. In the coexistence of these two components, the apparent catalytic activity of the solution changed in characteristic manners in response to the changes of temperature and of concentrations of the components in the reaction mixture. By quantitative studies of these phenomena it was concluded that the S-factor combines reversibly with the enzyme to form a heat-dissociable inactive complex.
2. The optimum temperature of the “free” catalase lies at 60°, while it shifts to 65° in the presence of the S-factor. The latter value coincides with the optimum temperature for the growth of the original thermophilic bacterium. The apparent activation energy of the enzyme reaction (in suboptimal temperature ranges) in the presence and absence of the S-factor was found to be about 14 and 3 Kcal./mole, respectively. The remarkably high value obtained in the presence of the S-factor was concluded to be a combined result of the dissociation of the S-factor from the enzyme and the activation of the enzyme reaction itself. Along the line of this inference and based on the results of experiments, in which the enzyme-S-factor-system had been pre-incubated at various temperatures and its enzyme activity was subsequently measured at 0°, it was deduced that the free energy of the dissociation of the inactive complex was 12 Kcal./mole.
3. The catalase freed from the S-factor behaved in respects of reaction kinetics-except for its remarkable temperature-tolerance-like ordinary catalase.
The author wishes to express his heartfelt gratitude to Prof. H. Tamiya, Prof. A. Takainiya, and Prof. K. Shibata for their guidance and valuable advices in carring out the experiments described here.