424 



IX. HEMATIN ENZYMES, II 



malachite green, (k2 + k3)/ki (over-all Michaelis constant) = 0.5 X 

 10-^ whereas experimentally {cj. 1862) 5 X 10"^ was found. The 

 combination with hydrogen peroxide is thus very rapid and practically 

 irreversible; ka is greater than k2. It could be measured more readily 

 with ascorbic acid than with leucomalachite green, since the forma- 

 tion of the dye is not a straightforward bimolecular reaction (c/. 1470). 

 No evidence for a chain reaction could be discovered, the induction 

 period being no longer than that required for the formation of the 

 peroxidase-hydrogen peroxide compound. The main difference 

 between peroxidase and catalase is the rapid irreversible breakdown 

 of the hydrogen peroxide catalase compound. 



3.2.5. Protein of Peroxidase. Peroxidase contains one protohem- 

 atin group (1.48%) in a molecule of molecular weight 44,000, as 

 established by measurement in the ultracentrifuge {2773). The 

 frictional ratio, ///o, is 1.36, corresponding to a prolate ellipsoid with 

 an axial ratio of 7. Theorell and Akesson {2786) have studied the 

 amino acid composition of horse-radish peroxidase by the electro- 

 dialytic micromethod and by estimation of the basic amino acids 

 (Table V). 



TABLE V 



Fractions of Horse-radish Peroxidase Hydrolyzate" 



" According to Theorell and Akesson (^7.*?^) . 



There is much less histidine in peroxidase (2 moles) than in catalase. 

 Peroxidase contains six atoms of sulfur. The nitrogen (13.2%) and 

 carbon contents are low. These data, the positive MoIi.sch reaction, 

 and the fact that on hydrolysis no less than 18.4% of the weight of 

 the peroxidase yielded humin substances of low nitrogen content, 



