SOME PROPERTIES OF CATALASE 407 



horse liver catalase. The iron of catalase itself has five unpaired 

 electrons. 



Earlier studies of Micliaelis and Graiiick {1938) had indicated three 

 unpaired electrons per iron atom, but these results were later withdrawn 

 {1937). Magnetocliemical studies on liver catalase are complicated by the 

 large diamagnetic contribution of the protein which forms 99% of the mole- 

 cule, and also by the fact that only about three quarters of the total iron is 

 hematin iron. The remaining quarter is bile pigment hematin iron, which 

 does not form covalent bonds with any of the reagents. The paramagnetic 

 contribution of this iron has to be subtracted in order to determine the 

 magnetochemical properties of the hematin iron in liver catalase. 



The absorption spectra of catalase and fluoride catalase are those 

 expected for compounds with an ionic type of linkage (c/. Chapter V, 

 Section 1.3.). The band of hydrogen sulfide catalase at 640 m^ may 

 be due to a partially ionic character of this compound. This is 

 supported by its magnetic susceptibility which is somewhat larger 

 than M'Ould be expected for a compound with covalent linkages. The 

 absorption spectra have also been measured spectrophotometrically 

 and the data of Keilin and Hartree (1499) are given in Figure 1. 

 Catalase also reacts with hydroxylamine, the first band becoming 

 more diflPuse and a shading at 580 m/x more noticeable {265Ii). 



The azide compound of catalase is quite different from that of 

 hemoglobin. While hemiglobin azide is a substance with covalent 

 linkages and a two-banded absorption spectrum, azide catalase has 

 ionic linkages and an absorption spectrum of the same type as that 

 of catalase itself. 



Of peculiar interest is the reaction of the azide compound with 

 hydrogen peroxide (Keilin, 1487,14.99). The red, two-banded absorp- 

 tion spectrum and the decrease in magnetic susceptibility prove that 

 hydrogen peroxide produces a compound with covalent linkages, 

 while in azide catalase the linkage is ionic. The absorption spectrum 

 of the red compound is shifted by carbon monoxide 10 m/u toward 

 the blue; this was confirmed by Theorell and Agner {2780). The 

 compound is stable under nitrogen, and is reconverted into azide 

 catalase by atmospheric oxygen, but not by ferricyanide. It does not 

 react with cyanide. Keilin therefore assumes that the compound 

 contains ferrous iron, hydrogen peroxide reducing the ferric iron of 

 azide catalase. 



While Keilin and Hartree previously spoke of azide-hydrogen 

 peroxide-carbon monoxide catalase, they avoid this term in their 

 latest paper {1499). Such compounds would require coordination 



