CATALASE 311 



SPECIAL REAGENTS 



Substrate Solution. 0.01 M hydrogen peroxide in 0.03 A^ phosphate 



buffer, pH 7.0. Prepare and keep at 0°. 

 Molybdic-Sulfuric Acid Solution. Make up 10 ml. saturated molyb- 



dic acid to 100 ml. with 33% sulfuric acid. 

 2% Potassium Iodide. 



0.2% Soluble Starch in 0.5% Potassium Iodide. 

 0.02 N Sodium Thiosulfate. 



PROCEDURE 



1. Pipette 5-7 fA. enzyme soln. into a reaction tube (Fig. 38, page 

 167) coated with ceresine (page 169). Add a mixing "flea," and cool 

 to 0°. 



2. Add 15 fA. substrate soln. from the cooled pipette. Mix, and 

 keep the liquid at 0°. 



3. After a 1-2 hr. reaction period at 0°, add 10 /xl. molybdic- 

 sulfuric acid soln. and 10 /xl. 2% potassium iodide. 



4. Immediately after adding the iodide, place a seal of 20 /^l. 

 starch soln. across the lumen of the tube about 5 mm. above the sur- 

 face of the reaction mixture to prevent loss of iodine. 



5. After 3 min., pass the tip of the microburette through the 

 starch film into the liquid below, and titrate with 0.02 N thiosulfate. 

 After most of the thiosulfate has been added, draw the starch film 

 down into the mixture and finish the titration. 



