184 V. HEMATIN COMPOUNDS 



of alkaline hematin. It resembles in shape that of the hemichrome 

 in neutral solution, but the bands are shifted toward the red and are 

 less intense. ief,^i = 5.8 to 6.1; ef^M = 6-5 to 6.6 {180,620,629). 

 Lemberg has made similar observations with monoazahemtchromes 



{1687). 



5. COMBINATION OF HEMATIN COMPOUNDS 



WITH OXYGEN, HYDROGEN PEROXIDE, 



CARBON MONOXIDE, AND CYANIDE 



5.1. Compounds with Oxygen and Hydrogen Peroxide 



The combination of hemoproteins with molecular oxygen and 

 hydrogen peroxide is of fundamental importance for the action of 

 respiratory carriers and enzymes concerned in tissue oxidation. Sub- 

 sequent chapters will deal in detail with the specific influence of the 

 protein on the direction of the reaction. The property of reversible 

 combination with oxygen is conferred almost entirely by the protein 

 to which heme is combined, and model experiments for this reaction 

 cannot be carried out with simple hematin compounds. In the latter 

 case combination with oxygen indeed occurs, but the compound is 

 unstable and the complex immediately goes over into the ferric state. 

 The unique properties of hemoglobin do not reside in the fact that 

 in it the heme is able to combine with oxygen, but in the fact that 

 the ferrous oxygen compound is stable. Its difference from the simple 

 hematin compounds is, however, only quantitative as even globin is 

 unable to prevent slow autoxidation. As will be shown later {cf. 

 Chapter X), it is necessary to postulate a short but definite lifetime 

 for the oxygen compounds of hemochromes. Thus Warburg's expla- 

 nation for the function of the respiratory ferment is not so unjustified 

 as it has been considered by some authors. Warburg assumed that 

 the ferrous form of the respiratory ferment first combines reversibly 

 with oxygen and that its iron is then oxidized to ferric state {cf. 

 Chapter VIII). 



There is a good deal of indirect evidence that heme compounds 

 can combine similarly with hydrogen peroxide, giving unstable com- 

 plexes in which not only does the iron later undergo oxidation to the 

 ferric state, but also other changes occur involving an oxidation of 

 the porphyrin ring. This will be discussed in Chapter X, since it 

 has been found by Lemberg to be the mechanism of bile pigment 

 formation. Hydrogen peroxide however, also combines with ferric 



