The Bond between Haem and Globin 



The two substituents linked to the iron atom are either atomic groups 

 of the same globin molecule (Formula III) or atomic groups of two 

 different globin molecules (Formula IV). Since it has been demonstrated 

 by S. Granick 3 that the haem group is situated on the surface of the 

 globin component and is accessible even to very large foreign molecules, 

 we prefer formula IV to formula III. This is also in better agreement 

 with x-ray measurements of M. F. Perutz 4 , who has shown that water 

 molecules coat the surface of the haemoglobin molecule. The correct- 

 ness of formula IV was tested experimentally by drying haemoglobin 

 in the presence of a large excess of glucose. It was expected that 

 glucose owing to its multiple polar groups would be attached to the 

 surface of the haemoglobin molecules and would, thus, prevent the 

 mutual association of these molecules to form the polymeric substance 

 IV. Actually we did not observe any haemochromogen spectrum when 

 1 ml of a 15 per cent solution of haemoglobin was dried in the presence 

 of 1-5 gm of glucose under the same conditions as those which had 

 brought about the absorption spectrum (c) in the absence of glucose. 

 We conclude from our experiments that the reversible reaction taking 

 place during the drying of haemoglobin must be represented by the 

 following equation : 



n Hb(H 2 0) ^ /z H 2 + (Hb) n 

 A quo-Haemoglobin Anhydro-Haemoglobin 

 {Spectrum b) {Spectrum c) 



Or, in other words, monomeric haemoglobin molecules can exist 

 only in aquous solutions or in wet crystals (Formula II). As soon as 

 the iron-linked water molecule is detached, polymerization of the 

 haemoglobin molecules occurs (Formula IV). On the other hand, 

 oxyhaemoglobin and carboxyhaemoglobin can exist as true molecules 

 in solutions as well as in the dry state (Formula I). 



It has been shown by L. Pauling and C. Coryell 5 and by H. 

 Theorell 6 that haemochromogens are devoid of paramagnetic suscepti- 

 bility. This is due to the deep penetration of coordinative substituents 

 into the electron shell of the iron atom. The magnetic momentum of 

 the 3d electrons is lost as soon as they become involved in the bonding 

 of the coordinative substituents. We suppose, therefore, that haemo- 

 globin loses its paramagnetic susceptibility on drying. One has to 

 assume, moreover, that the iron-bound water molecule of haemoglobin 

 is bound less firmly than the oxygen molecule of oxyhaemoglobin and 

 that the 3d electrons are not involved in the bonding of the water 

 molecule. 



Discussion — The main result of the presented experiments is the 

 revelation that oxyhaemoglobin does not dissociate into haemoglobin 



55 



