482 X. BILE PIGMENT FORMATION, ETC. 



and Singer {21JfIi.,21J!i.o), it appears likely that the same systems cause 

 destruction of bacterial toxins in the presence of hematin compounds; this 

 may be of physiological importance. 



5. "EASILY DETACHABLE IRON" 

 AND NONHEMOGLOBIN IRON IN BLOOD 



5.1. Easily Detachable Iron 



In several papers Barkan and co-workers (150,153,155,157,159,161, 

 163) have shown that a part of the iron in erythrocytes and also in 

 crystalline oxyhemoglobin is split off by dilute hydrochloric acid. In 

 ox blood, for example, 4-6% of the total blood iron can be set free 

 in this way, in horse and dog blood more, in man and rabbit perhaps 

 somewhat less. No free porphyrin is formed. The plasma iron forms 

 only a small percentage of this "easily detachable iron" (0.1-0.2%), 

 and the contribution of the stroma is still smaller. Barkan's results 

 were confirmed by several other authors, although the percentages 

 of "easily detachable iron" found by different methods varied a 

 good deal. Barkan assumed the easily detachable iron to be derived 

 from a bile pigment hemoglobin which was assumed to be present 

 in erythrocytes and even to accompany oxyhemoglobin in the crystals. 

 Lintzel (1753,1755), however, believed it to be derived from oxyhemo- 

 globin itself, since less acid hematin color was developed on acidifi- 

 cation from oxyhemoglobin than from carboxyhemoglobin solutions; 

 this was confirmed but differently interpreted by Barkan. 



Barkan and co-workers (157) observed that the presence of carbon 

 monoxide and also reduction to hemoglobin prevented the setting 

 free of about two thirds of the easily detachable iron. This was 

 confirmed by Legge and Lemberg (1668). The iron of choleglobin, 

 however, is removed in the presence of carbon monoxide as well as 

 in its absence. From this and from a critical discussion of Barkan's 

 experiments, they arrived at the conclusion that only about one third 

 of the easily detachable iron which could be removed in the presence 

 of carbon monoxide is derived from a bile pigment hemoglobin 

 present in the erythrocytes, while the remaining two thirds is formed, 

 from oxyhemoglobin by the action of the acid. 



It has been shown in Chapter Vlll, Section G.3.6.. that on acidification 

 the oxygen of oxyhemoglobin becomes strongly active and able to oxidize 

 parts of the hemoglobin molecule. Several authors, including later Barkan 

 himself (165,333,2613,2^65), have shown that the amount of easily detachable 



