NATURE OF PROSTHETIC GROUP IN CATALASE 413 



as due to "pliilocatalase." In Section i. these phenomena will be discussed 

 in relation to the theory of the mode of action of catalase. They deserve a 

 reinvestigation with modern methods. 



2.5. Nature of the Prosthetic Group 



Zeile and Hellstrom (3166) demonstrated that alkali, pyridine, and 

 dithionite transform horse Hver catalase into a hemochrome which is 

 spectroscopically indistinguishable from pyridine protohemochrome. 

 By treatment with hydrazine and acetic acid this was transformed 

 into protoporphyrin. Crystalline hemin was isolated from catalase 

 by Stern {2652) and transformed into mesoporphyrin dimethyl ester. 

 By mixed melting point determinations it was shown that this was 

 mesoporphyrin IX ester. The prosthetic group of catalase is thus 

 the same as that of hemoglobin. 



Bile pigment in catalase. From a fraction of Stern's preparation, 

 Lemberg {cf. 2652) isolated biliverdin. This later became of interest 

 when Summer and Dounce (2699) showed that their crystalline ox 

 liver catalase did not contain four hematin groups per molecule, as 

 had been claimed by Stern and WyckoflF {2661), but only two, the 

 remainder of the iron (two atoms per molecule) being accompanied 

 by a blue substance after treatment with acetone -hydrochloric acid. 

 The blue substance was again identified as biliverdin by Lemberg and 

 co-workers {1705,171 If.). They showed that biliverdin was not present 

 in the catalase as such but was detached from a bile pigment hematin 

 by treatment with acid. The presence of this hematin was also 

 revealed by the absorption curves of the hemochrome obtained from 

 the catalase by treatment with alkali and dithionite. 



Lemberg and Legge as well as Agner {27) found about three of the 

 four iron atoms of the molecule of ox and horse liver catalase to be 

 protohematin groups. The fourth iron was ascribed by Lemberg to 

 the bile pigment hematin group, while Theorell {2771,2778) and Agner 

 {27) considered the proportionality of iron and biliverdin to be 

 accidental. Lately, however {29), these authors have themselves 

 found additional evidence for the presence of a hematin group differ- 

 ent from protohematin in liver catalase.* 



There is no conclusive evidence today to show whether protohematin and 

 bile pigment hematin groups occur in one and the same molecule, or whether 

 liver catalase is a mixture of active catalase — containing four protohematin 



* Human liver catalase apparently does not contain this group (unpul)lished 

 experiments cited by Theorell, 27J9a). 



