Ferrihaemoglobin in Normal Blood 



W. N. M. RAMSAY 



The paper is a review of published work in the field covered by the 

 title. Possible methods of formation and removal of ferrihaemo- 

 globin* in normal erythrocytes are discussed. Gasometric deter- 

 minations of ' inactive haemoglobin ' are described and compared 

 with spectrophotometric determinations of ferrihaemoglobin. The 

 conclusion is reached that at the most only a small proportion of 

 the so-called ' inactive haemoglobin ' can be accounted for as 



ferrihaemoglobin . 



The extraordinary ability which ferrohaemoglobin possesses, of 

 combining with molecular oxygen to form a covalent compound, is 

 apt to overshadow the fact that ferrohaemoglobin is an oxidizable 

 substance and that oxygen might reasonably be expected to function 

 as an oxidizing agent. This aspect of the reaction was studied some 

 years ago by J. Brooks 1 , 2 , who found that the rate of oxidation to 

 ferrihaemoglobin appeared to follow a course which was unimolecular 

 with respect to unoxygenated ferrohaemoglobin. He also found the 

 rate of oxidation to be proportional to a function of the pressure of 

 oxygen, which increases in value as the pressure increases. Since 

 raising the oxygen pressure tends to increase the rate of oxidation 

 (through the oxygen pressure factor), and simultaneously to decrease 

 it (by converting a larger proportion of the other reactant, ferro- 

 haemoglobin, to the apparently inert oxygenated form) it should be 

 possible, by making experiments at different oxygen pressures, to find 

 a point of balance between the opposing tendencies where the rate of 

 oxidation to ferrihaemoglobin is maximal. Brooks found indeed such 

 a point. Under the conditions of his experiments, at /?H 5-69, it was 

 near 20 mm. Although these experiments were done at a pH which 

 hardly falls within the mammalian physiological range, there seems 

 to be no reason to expect that his results would not hold at least 

 qualitatively at pH 7-4. If that be granted, it seems clear that the 

 normal erythrocyte contains a mechanism which must tend to produce 

 ferrihaemoglobin, especially on the venous side of the circulation, 

 where there is much unoxygenated ferrohaemoglobin and yet still a 

 quantity of available oxygen. 



* The terms ferrihaemoglobin and ferrohaemoglobin are used throughout this paper 

 in place of methaemoglobin and haemoglobin". 



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