242 



E. Margoliash and A. Schejter 



within 90 min, with a haemolysate representing a 1 : 10 dilution, as compared 



to a 30% inhibition in 120 min at an ascorbate concentration of 2 x 10~^ m. 



Thus either a decrease of the haemolysate concentration or an increase of 



the hydrogen peroxide concentration resulted in an increased rate of inhibition. 



Effect of Dialysis on the Rate of Inhibition of Catalase by 3-aniino-\:2:4- 

 triazole in Rat Erythrocyte Haemolysates 



Figure 1 shows that when rat erythrocyte haemolysates were dialysed, the 

 substance or substances responsible for preventing the AT inhibition of 

 catalase in the presence of hydrogen peroxide rapidly disappeared. Within 

 6 hr of the beginning of dialysis the rate of catalase inhibition was essentially 

 the same in the dialysed haemolysate as with purified catalase preparations 

 (Margoliash et al., 1960). 



Effect of N-ethyhnaleimide on the Inhibition of Catalase by 3-amino-l:2:4- 

 triazole in Rat Erythrocyte Haemolysates 



Table 2 shows that with a relatively concentrated rat erythrocyte haemo- 

 lysate no inhibition of catalase by AT could be obtained under the usual 



Table 2 



Effect of N-ethylmaleimide on the inhibition of catalase activity in rat 

 erythrocyte haemolysates by 3-amino-l :2:4-triazole. Final concentra- 

 tions: 1 : 5 dilution of packed rat erythrocytes and 5 x 10"^ m ascorbate 

 present in all incubation mixtures; 0-02 m NaHCOg buffer at pH 8-5 or 

 0-02 M 2-amino-2-hydroxymethylpropane-l :3-diol-HCl buffer at pH 7-2; 

 0-02 M AT; 0002 M N-ethylmaleimide. The solutions were incubated 

 for 90 min at 37°C in air. At the end of the incubation, samples were 

 suitably diluted and catalatic activity was determined : 



conditions. However, the addition of N-ethylmaleimide, which itself had no 

 effect on catalatic activity, completely reversed the protection of catalase in 

 the haemolysate resulting in a normal rate of inhibition of the enzyme. 



DISCUSSION 



The physiological role of catalase particularly in tissues rich in the enzyme 

 such as liver, red blood cells and kidney, has been the object of numerous 



