STUDIES ON THE REACTION BETWEEN CATALASE MOLECULE AND VARIOUS INHIBITORY SUBSTANCES, I
1950 年 37 巻 2 号 p. 153-177
詳細
1950 年 37 巻 2 号 p. 153-177
1) The reaction between catalase molecule and various inhibitory substances was studied quantitatively by using both kinetic and spectrophotometric methods.
2) The characteristic spectrum of catalase is changed by its combination with cyanide, chloride, fluoride, sulfide, azide and hydroxylamine, while no change could be observed by that with phenol, resorcinol, hydroquinone, cresols, chlorophenols, nitrophenols and hydrogen ion, though these strongly inhibit catalase activity. Substances of the latter group may be regarded as exerting their inhibitory action by combining with certain structual element in protein moiety of the catalase molecule.
3) In the absence of inhibitors, the Iog[H2O2]-time-curve observed in the catalatic H2O2-decomposition represents, as is well known, a straight line at lower temperatures and within certain limits of H2O2 concentration applied. In the presence of inhibitors, however, the log[H2O2)-time-curve usually bends more or less convexly towards the time-axis. The exception was found only in cyanide in which the log[H2O2]-time -curve represented a straight line as in the control experiment. The bending curves were found to be composed of two straight lines with different tangents, and for the corresponding two states of inhibition, referred to as the which is in accordance with the fact that in the absence of inhibitors the log[H2O2]-time-curve represents a straight line.
In the presence of an inhibitor the following two reaction will occur besides the above-mentioned three:
E+G_??_EG (IV)
SE+G_??_SEG (V)
Assuming that both these reactions can take place rather slowly, it was deduced that the φ-values found in the “initial” and “final” S states are the dissociation constants of EG and SEG, respectively, the former having larger dissociation constant than the latter. Among all the inhibitors studied, cyanide occupies a special position, in which reactions (IV) and (V) seem to occur very rapidly with the dissociation constants not differing from one another.
This investigation forms a part of the study of the Research Commitee of Heavy Metal Catalysis of the National Research Council and was supported by a grant donated to one of the authors (Tamiya) by the Ministry of Education.
