HAEMOGLOBIN SYSTEMS 49 



More recently, however, Conant and Pappenheimer (1932) find that the electrode 

 potential of the 50 per cent, oxidised system is + 0-152 v. at pH 7, and that the 

 number of electrons concerned in the reaction varies between 1 and 2-5. Unless 

 auxiliary assumptions are made this is not in agreement with the requirements of the 

 simple reaction : — 



Hb4 — 4 electrons -> MHb4 



Havemann and Wolff (1937) found the potentials were reached rather slowly, 

 but that they could be accounted for by the equation : — 



^ .o. I^T ^^ RT , [MetHb] 

 E = + 0-526--jr X pH + -^r In '^^jbT 



In this equation again a single electron appears to participate in the Haemoglobin- 

 Methsemoglobin reaction. 



Conant and Tongberg (1930) have studied the system parahaematin-hsemo- 

 chromogen and conclude that at pH 7 -5 the electrode potential of the 50 per cent, 

 oxidised system {i.e., Eq) is — 0-1 volt. 



Hsemochromogen systems have been studied also by Barron (1937). Cyan- 

 haimochromogen was found to give rapid potentiometric equilibrium, the results 

 being independent of pH and referable to a univalent system. With pyridine- 

 hsemochromogen the potentials varied with pH from those of a univalent to a 

 divalent system, and alkaline hsemin was found to be dimeric. 



Taylor and Hastings (1939) have reported on the oxidation-reduction potential 

 of the hsemoglobin-methsemoglobin system and Taylor and Morgan (1942) on the 

 myoglobin-methsemoglobin system. 



Barron (1940) has studied SpirograpJiis hsemin (1:3:5:8 -tetramethyl -2- 

 formyl-4-vinylporphine-6 : 7-dipropionic acid iron chloride) and finds the E^^ 

 values at 30° to be— 0-089 v. at pH 7-22 and — 0-230 v. at 9-63. The potentials of the 

 hsemochromogens are: cyanide— 0-113 v. at pH 9-95; pilocarpine — 0-067 v.; 

 a-picoline— 0-01 v. at pH 9-63. 



Lepper and Martin (1929, 1930) have examined t?ie meat medium used for 

 cultivation of anaerobes and find an electrode potential of about Ej^ — 0-2 volt. They 

 conclude that the potential is established by the following mechanism : lipins 

 absorb oxygen from the culture medium by virtue of the unsaturated acids they con- 

 tain, the presence of haematin being necessary to catalyse the autoxidation. In 

 addition to this reduction process there is diffusion of the parahsematin-hsemochro- 

 mogen system from the cooked meat. They point out that a potential of —0-18 volt 

 would indicate 95 per cent, reduction and— 0-22 volt, 99 per cent, reduction of the 

 parahaematin system. The potentials they obtained agreed with the extent of 

 reduction inferred from the bright pinlc colour observed in the bottom of meat media 

 tubes where the medium is furthest removed from contact with air. 



In considering the chain of reactions by which foodstuffs in the body are oxidised, 

 haemoglobin comes at the very end of the chain (or the beginning according to the 

 point of view). It provides the transport by which air is carried by the lungs to the 

 cells and tissues which require it. One of the penultimate links is provided by 

 cytochrome which is dealt with in the next section. Both haemoglobin and the cyto- 



