190 



V. HEMATIN COMPOUNDS 



hydrocyanic acid (;>K 9.1) (303). Further, the possibility that the compound 

 is one of heme with hydrocyanic acid is excluded by the same effect. In 

 Table VII the dis.sociation constants are given on the basis of the simple 

 equations : 



[Fe] + CN ^ [FeCN] 

 [FeCN] +CN^[Fe(CN)2] 



the constant for the dicyanide ferroporphyrin being the product of those 

 derived from the two equations. 



5.3.3. Mixed Cyanide-Base Hematins. Hill (1277) found that 

 nicotine hemochrome combines more readily with cyanide than does 

 heme, and Anson and Mirsky (74) prepared a similar denatured 

 globin cyanide hemochrome. Krebs (1578), and Drabkin (620) found 

 that pyridine, nicotine, and denatured globin hemichromes unite 

 with cyanide at much lower concentrations than does hematin. The 

 compounds so formed are of particular importance in that the cyanide 

 inhibition of the respiratory ferment consists in the formation of a 

 similar cyanide protein ferriporphyrin. 



The available data do not indicate the nature of the equilibrium, or its 

 dependence on pH, or even the nature of the complex formed. The latter 

 may conceivably be any one of tlie following (for the ferric form) : 



-iO 



If formula / is correct, the charge on the cyanide ba.se complex differs 

 from that on the dicyanide complex; however there is no difference in spectral 

 type between these two compounds, nor between them and hemoglobin 

 cyanide, except that dicyanide ferriporphyrin has a lower and less distinct 

 Soret band. The second formula is supported by Krebs" observation that 

 combination with cyanide is not proportional to cyanide concentration. The 

 third requires the reaction to be pH dependent; although whether this is so 

 or not is unknown, there is no change of spectrum with /;H. Both the 

 second and third formulas require the assumption of hepta coordination, 

 which has already been made by Clark for the hem/chromes themselves.* 



Except in the ca.se of nicotine cyanide ferroporphyrin and denatured globin 



* Formula I is supported by the recent work of Shack and Clark {2538a). 



