By thermal analysis of the reaction velocity, the influences of cyanide and azide upon the catalatic reaction by blood catalase (red cell suspension and hemolysate) has been examined. As cyanide and azide, KCN and Na N₃ were used. The inhibition of the reaction has been discussed from the stand-point of adsorption theory. The results obtained are summarized as follows:
(1) The reaction type is not different by the addition of cyanide from that of the standard reaction in the absence of cyanide and is mainly of the first order, except at the initial stage. As the amount of cyanide is increased, the duration of time of the initial stage increases and the velocity constant of the first order reaction decreases.
(2) The reaction type deviates from that of the standard reaction at the initial stage when azide is added, but is mainly of the first order. The velocity constant of the first order reaction decreases as the amount of azide is increased.
(3) CN^-and N^-₃ions have a special affinity and can be selectively adsorbed on the blood catalase surface and retard the reaction velocity by ionic adsorption which is the absorption of potential determining ion.
(4) From the relation between the activity and the concentration of azide, it is considered that there are at leat two kinds of active centres in a blood catalase molecule and N^-₃is combined with one of the two alone.