414 IX. HEMATIN ENZYMES, II 



groups — with inactive oxidized catalase — containing four bile pigment 

 hematin groups. Sumner and Lemberg have both shown that the ratio of 

 protohematin to bile pigment liematin varies {cf.,e.g., 61^), although usually 

 within rather narrow limits, and that the catalase activity decreases with 

 increased bile pigment hematin content. Hybrids may exist, but then 

 interaction between dissimilar hematins has not been demonstrated. If the 

 mixture contains active and inactivated catalase, the proteins to wjiich the 

 different prosthetic groups are attached must be the same. The rather constant 

 proportion must then be conditioned physiologically rather than chemically. 

 This is supported by the fact that erythrocyte catalase does not contain any 

 bile pigment hematin (Laskowski and Sumner, lGd7; Agner, 28). These 

 observations are of interest with regard to the role of catalase in vivo. This 

 aspect will receive consideration in a later section. A claim of Agner (24) 

 that copper is an essential part of the catalase molecule w'as withdrawn {25). 



2.6. Protein of Catalase 



Catalase is not as stable as cytochrome c, but is not as readily 

 denatured as hemoglobin. At 0° C. it can be kept for a long time. It 

 has been claimed, however, that very dilute solutions soon lose their 

 activity. By means of ultracentrifuge experiments the molecular 

 weight of ox and horse liver catalase was found to be 225,000 {2700, 

 2702); Stern and Wyckoff {2661) had previously reported a similar, 

 but somewhat higher value of 250,000 to 300,000. From the iron 

 content — 0.0947o of horse liver catalase {27), 0.087% of erythrocyte 

 catalase {28) — a molecular weight of 238,000 can be calculated for the 

 former, and of 257,000 for the latter — assuming four atoms of iron 

 per molecule. At /:>H 9.9 the molecule splits into smaller units. 



The isoelectric point of crystalline ox liver catalase is 5.7 {2698); 

 for horse liver catalase values between 5.4 and 5.6 have been reported 

 {25, 26If5, 261^6). Theorell and Akesson {2786) have studied the 

 hydroly^ate of horse liver catalase with a new electrodialytic micro- 

 method, and have investigated the content of basic amino acids. 

 The results are given in Table III. The asymmetry ratio of 4.8 was 

 observed for anhydrous, that of 3.4 for hydrated, catalase {2045). 



Catalase is an antigen; the antibody-catalase precipitate is cata- 

 lytically inactive {399). Horse liver catalase differs immunologically 

 to a greater extent from ox liver catalase than does sheep liver 

 catalase {2828). 



Practically nothing is known as yet about the linkage of the 

 prosthetic group to the protein, which confers an extraordinary 

 stability on the ferric form of the former. Agner {23) had claimed 

 that catalase could be split reversibly if the enzyme was dialyzed 



