218 VI. HEMOGLOBIN 



hemoglobin is formed during the complex reactions which take place between 

 oxyhemoglobin and phenylhydroxylamine (c/. Chapters VIII, 6.3.3., and 

 XI, 5.3.). 



2.3. Properties of Ferric Compounds 



2.3.1. Hemiglobin (Methemoglobin, Ferriheitioglobin, Hi). 



Heniiglobin may be formed from any of the hemoglobin derivatives 

 by the action of reagents such as potassium ferricyanide which 

 oxidize the iron to the ferric state. Its structure as ferric hemoglobin, 

 first postulated by Kiister and his pupils (2227), was proved by 

 Conant and co-workers {Jf.70,Ji.78,If79). Hemiglobin may also be 

 formed by the autoxidation of oxyhemoglobin (Chapter VIII, 6.3.5.) 

 or by coupled oxidation. The equilibrium between hemo- and hemo- 

 globin is discussed in Section 5.1.7. Hemiglobin is frequently found 

 as an abnormal blood pigment (c/. Chapter XI, 5.2.). 



The solutions are brown and the compound has a four-banded 

 absorption spectrum with a band in the orange-red at 630 mju which 

 may be detected in the presence of a twentyfold excess of oxyhemo- 

 globin. Magnetochemical measurement has shown the existence 

 of five unpaired electrons; the bonds are therefore of an ionic type 

 U99,502). 



Hemiglobin may be written as having the formal structure (c/., 

 however, Section 3.2.2.5.) given below. In alkaline solution a proton 

 is removed from this system and hemiglobin hydroxide is formed 

 (Section 2.3.2.), in which the residual hydroxy! is less readily replaced 

 by other groups. The groups which combine with hemiglobin are 

 frequently different from those which combine with hemoglobin. 



N N 



globin Fe"'"— OH2 



PC N 



2.3.2. Hemiglobin Hydroxide (Alkaline Methemoglobin, 



HiOH). Hemiglobin carries a positive charge and as the pH becomes 

 greater than 7, the sixth bond position of the iron becomes occupied 

 by an hydroxy! ion. A change in the magnetic susceptibility occurs. 

 The band in the red diminishes in intensity and shifts to 600 m/x, 

 while the weaker bands in the remainder of the spectrum (577 and 

 540 m/i) become more pronounced; the spectrum shows some simi- 

 larity to that of oxyhemoglobin. It resembles still more closely that 



