COMPOUNDS WITH OXYGEN AND HYDROGEN PEROXIDE 185 



heinatin iron. While the pohirographic evidence for the existence 

 of heniatin-hydrogen peroxide complexes {,330) was later withdrawn 

 {331), Haurowitz {1169,1172) has observed that pyridine hem/chrome 

 forms an hydrogen peroxide complex having al)sorption bands at 

 590 and 570 m^. Similar compounds of hemiglobin have been 

 studied by several authors (Chapter VI) while other compounds of 

 the same type are formed by peroxidase and catalase (Chapter IX). 

 According to Euler and Josephson {721) the affinity of hematin for 

 hydrogen peroxide is greater than that of catalase. 



5.2. Carbon Monoxide Compounds 



The importance of carbon monoxide and cyanide as inhibitors in 

 the study of biologically important hematin enzymes has already 

 been stressed in Chapter I and will be <liscussed in greater detail in 

 Chapter VIII. Carbon monoxide combines only with ferrous heme 

 derivatives. 



That both heme and hemochromes in absence of excess of combined 

 nitrogenous substance, combine with one molecule of carbon monoxide 

 has long been known {65,1276,1277,13^,1356,1957,2185). F. Pregl 

 {2185) obtained a carbon monoxide hemochrome in solid form, and 

 demonstrated that ferricyanide liberated one mole of carbon monoxide 

 per mole of heme. There are, however, some ferrous heme derivatives, 

 such as cytochrome c, which do not combine with carbon monoxide. 



5.2.1. Carbon Monoxide Heme. Earlier workers found that heme 

 combines with carbon monoxide only in alkaline solution, but it was 

 later shown that this was due to the slower rate of reaction in acid 

 solutions, possibl\' flue to the polymerization of the heme. The 

 final equilibrium is not altered {J^56). A formula in which the sixth 

 point of coordination is filled by a molecule of water was suggested 

 by Hill {1277). Warburg {29^9) found that one light quantum 

 dissociates one molecule of carbon monoxide heme. 



5.2.2. Carbon Monoxide Hemochromes. Carbon monoxide heme 

 combines with bases like i)yri(line to form carbon monoxide hemo- 

 chromes but an excess of pyridine expels the carbon monoxide. 

 Carbon monoxide hemochromes were observed by Anson and Mirsky 

 {65) and l\. Hill {1276,1277). Krebs {1578,1579) found that they 

 are more readily dissociated by light than is carbon monoxide heme. 

 The equilibrium of the reaction: 



[Fe pyr,] + CO ;=± [Fe pyr CO] + pyr 



