166 BIOLOGICAL CHEMISTRY 



number of molecules of haemoglobin is reduced and the mass 

 law relations are altered. 



A. V. Hill suggests the following equation : * -2 = 



100 



where y = percentage saturation of the hemoglobin with 

 oxygen, x = oxygen pressure, K is the equilibrium constant 

 of the curve, and n = average number of haemoglobin mole- 

 cules in the aggregations. This equation agrees with the 

 experimental results. 



THE NATURE OF THE COMBINATION OF OXYGEN WITH 

 HEMOGLOBIN 



One of the criteria of a chemical combination is that there 

 must be a definite fixed relation between the number of atoms 

 united in the molecule, hence we must find out the molecular 

 weight of haemoglobin and the number of atoms of oxygen 

 united with the haemoglobin. 



The minimum molecular weight of haemoglobin has been 

 calculated from the percentage of iron contained in it. 

 Haemoglobin contains about 0*4 per cent, of iron. The 

 minimum molecular weight is therefore about 14,000. 



Direct measurements of the molecular weight of haemoglobin 

 are difficult to obtain, but Hufner and Gansser found that 

 under the conditions of their experiments the osmotic pressure 

 of haemoglobin solutions indicate a molecular weight of 

 about 16,000. (Horse = 15,115. Cow = 16,321.)! 



The values obtained depend upon the condition of the 

 haemoglobin in the solution as acid, alkali and salts markedly 

 affect the condition of the haemoglobin. J 



The amount of haemoglobin containing i gram of iron' 

 when completely saturated with oxygen absorbs 401 c.c. of 

 oxygen at o and 760 mm. pressure. Therefore for each 

 atom of iron haemoglobin absorbs two atoms of oxygen, 

 thus showing a definite atomic relationship between the iron 

 and oxygen in the haemoglobin. 



Barcroft and Hill have made measurements of the rate of 

 reduction of haemoglobin at different temperatures. From 

 these rates they calculated the molecular heat of combination 

 of one molecule of haemoglobin with oxygen. They measured 

 the heat produced when one gram of haemoglobin unites 



* A. V. Hill, Journ. Physiol., 1910, vol. 40, Proc. p. iv. 



f G. Hufner and E. Gansser, Arch. f. Physiol. , 1907, p. 209. 



t H. E. Roaf, Quart. Journ. Exper. Physiol., 1909, vol. 3, p. 75. 



R. A. Peters, Journ. Physiol. , 1912, vol. 44, p. 131. 



