LIBERATION OF HEMATIN IRON 561 



The small margin between the bilirubin excretion, as calculated from the 

 lifetime of the erythrocytes or from disappearing hemoglobin in Whipple's 

 experiments, and that found experimentally (cf. Section 3.) makes it appear 

 unlikely that any catabolism of hemoglobin which does not lead to bilirubin 

 is of major significance. This excludes for instance the possibility that the 

 coupled oxidation of hemoglobin and fatty acids (Haurowitz and co-workers, 

 1176), which leads to colorless products, occurs physiologically on a large 

 scale. 



10. LIBERATION OF HEMATIN IRON 

 AND FATE OF GLOBIN 



10. 1. Introduction 



The human body contains between 3 and 5 g. iron, significantly 

 more in men than in women. Of this about 60% (2.8 g. in man, 

 1.9 g. in woman) is present as hemoglobin in the erythrocytes. Of 

 the remainder 0.3 g. or more has been estimated to be present in the 

 tissues, as myohemoglobin in the muscles, and in much smaller 

 amounts as respiratory enzymes in all tissues. About 1.3 g. is present 

 as storage iron in organs, mainly in the liver and spleen, while a few 

 milligrams represent the transport iron of the plasma. 



Iron is found in the animal body principally in two chemical forms: 

 hematin iron and nonhematin iron. The former is represented by 

 hemoglobin, myohemoglobin, and the respiratory catalysts. Wher- 

 ever one of these compounds, mainly of course hemoglobin, is broken 

 down to bile pigment, iron is set free. 



A third form of iron exists which is intermediate between hematin 

 and nonhematin iron. This is the bile pigment hematin iron, which 

 is easily detached by acids {cf. Chapter X). So far no method has 

 been found by which it would be possible to distinguish directly 

 between it and nonhematin iron; the evidence is indirect and based 

 on the spectroscopic properties of the compounds. 



The nonhematin iron again comprises a variety of iron compounds. 

 The iron may be in the ferrous or in the ferric state. It may be pres- 

 ent as an inorganic compound, e.g., as pyrophosphate, or bound to 

 protein, probably in more than one way. 



Knowledge of iron metabolism has recently begun to make rapid 

 progress, largely due to the use of radioactive iron (Fe'') {cf. the 

 reviews lOSIf, 1086, 1199, 1765, 2129a) and still more recently, of 

 Fe". Using Fe^^ Ruben and co-workers {2S89a) have shown that 

 there is no exchange between hematin iron and ionic iron. Many 

 erroneous ideas have had to be abandoned. 



