222 VI. HEMOGLOBIN 



hydrogen peroxide is decomposed peroxidatively without liberation 

 of oxygen, a portion of the hemoglobin being destroyed in the process 



{U85)- 



2.3.9. Compounds with Cyanate and Thiocyanate. Spectroscopic investi- 

 gation has shown the existence of a number of other substances which are 

 able to combine with hem/globin. Among these are fulminate (173), cyanate 

 (1200,2472), and thiocyanate (1442). The spectral changes occurring when 

 the latter two compounds combine with hemoglobin are slight, the spectrum 

 being of the same character as that of hem/globin, with slight differences in 

 the position and height of the absorption bands. 



Havemann (ILS'S) has investigated the equilibrium between thiocyanate 

 and hem/globin. Since thiocyanic acid is a strong acid, only two cases need 

 be considered : 



Hi+ + SCN- ^HiSCN (a) 



HiOH + SCN- ^ HiSCN + OH" (b) 



The first of these is not sensitive to pH changes, and pK = 3.14. The second 

 equiHbrium is pH dependent, pK = 9.8.* The affinity of hemiglobin for 

 thiocyanate falls between that for fluoride and that for cyanide. The mag- 

 netic susceptibilities of these compounds have not yet been measured. 



2.3.10. Other Hemiglohin Compounds. Ethanol and ammonia have been 

 claimed to form compounds with hem/globin hydroxide (501), the ethanol 

 compound having five unpaired electrons (ionic bonds), while the ammonia 

 compound has one unpaired electron (covalent bonds). 



For the reaction HiOH + C2H5OH ^ HiOH • C2H5OH, pK = 0.41; for 

 the reaction HiOH + NH3 -* HiOH • NH3, pK = 0. If these reactions have 

 been interpreted correctly, the resulting compounds contain iron in hepta- 

 valent coordination (four Imkages to porphyrin nitrogens, one to globin, one 

 to hydroxyl, and one to ethanol or ammonia); cf. Chapter V, Section 4.2.3. 



In ammonia hem/globin hydroxide, six covalent bonds resonating between 

 seven linkages would have to be assumed. 



With imidazole, hem/globin forms a compound whose spectrum resembles 

 that of hem/globin hydroxide (2397). Imidazole hem/globin has one unpaired 

 electron and hence covalent bonds. The imidazole is not very firmly bound 

 to the hem/globin (pK = about 2.7 at pH 7). 



2.4. Denatured Globin Hemochrome 

 and Other Protein Hemochronies 

 2.4.1. Denatured Globin Hemochrome. For the preparation of 

 substances so far dealt with, conditions have been chosen so that 

 minimal change has occurred in the proteins. If the pH of a solution 

 of hemoglobin is shifted much beyond pH 11, denatured globin hemo- 



[HiOH] [SCN- ][H+ ] 

 ^ ~ [HiSCN] 



