The Bond between Haem and Globin 



FELIX HAUROWITZ* 



1 The iron atom of reduced haemoglobin is saturated coordin- 

 atively by a water molecule instead of0 2 . Haemoglobin is an aquo- 

 compound. 



2 Oxy haemoglobin cannot dissociate into haemoglobin and oxygen 

 in the absence of water. The equilibrium between haemoglobin and 

 oxyzen is represented by the equation : Hb(H 2 0) + 2 ^ Hb0 2 

 + H 2 0. 



3 The influence of salts, hydrogen ions and of the globin com- 

 ponent on the equilibrium is attributed to the action of these sub- 

 stances on the iron-linked water molecule. 



The most important reaction of haemoglobin is certainly its combina- 

 tion with oxygen to form oxyhaemoglobin. This reaction is represented 

 by the well-known equation Hb + 2 ^ Hb0 2 . Although this equa- 

 tion is accepted quite generally, it does not correspond to the actual 

 reaction taking place between haemoglobin and oxygen. This can be 

 shown by two simple experiments. 



The first of them consists in drying oxyhaemoglobin cautiously and 

 then exposing the dry preparation in a vacuum. It is found, that the 

 typical colour and the absorption spectrum of dry oxyhaemoglobin do 

 not undergo any alteration, even if the pressure is reduced to 0- 1 mm 

 of Hg. Under the same conditions wet oxyhaemoglobin crystals or 

 oxyhaemoglobin dissolved in water pass instantaneously into haemo- 

 globin. 



Layers of dry oxyhaemoglobin were obtained by the evaporation of 0-5 ml of 

 a 5 per cent solution of beef oxyhaemoglobin. The solution was placed in a glass 

 dish and kept in a desiccator under slightly reduced pressure over large amounts 

 of phosphorus pentoxide, so that drying was achieved within few minutes. Only 

 traces of methaemoglobin were formed under these conditions. 



The conclusion from this experiment is that the oxygen molecule 

 cannot be detached from haemoglobin in the absence of water. This 

 is in agreement with our view, advanced several years ago 1 , that 

 haemoglobin is an aquo-compound, in which one water molecule is 

 bound coordinatively to the iron atom (Formula II). 



This view is supported by a second series of experiments, in which 

 we attempted to detach the water molecule from reduced haemoglobin. 

 It had been shown, previously, by R. von Zeynek 2 that reduced 



* Present address : Department of Chemistry, Indiana University, Bloomington, 

 Ind., U.S.A. The experiments were carried out in the Department of Medical Chemistry, 

 University of Istanbul (Turkey) with the assistance of Radiye Cindi and Saide Tun?. 



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