

THE INDIVIDUAL GROUPS OF PROTEINS 481 



Cyanhaemoglobin. HbCN. 



Solutions of oxyhaemoglobin are converted into cyanhaemoglobin when 

 they are mixed with potassium cyanide or hydrogen cyanide and allowed to 

 stand or warmed to 40. The colour becomes orange-yellow (Preyer). 



Solutions of methaemoglobin are changed immediately into cyanhaemoglo- 

 bin when they are treated with -5 per cent, hydrogen cyanide solution (Kobert). 



Alkaline solutions of methaemoglobin also yield cyanhaemoglobin on 

 treatment with potassium cyanide. 



Cyanhaemoglobin is also a stable compound and contains -158 per cent, 

 of CN. It shows a broad absorption band in the green. 



It is converted into haematin by the action of sodium hydroxide ; haematin 

 gives cyanhaematin with hydrogen cyanide ; cyanhaematin, on reduction with 

 ammonium sulphide, gives cyanhaemochromogen and haemochromogen. 



Sulphhsemoglobin. 



Sulphhaemoglobin is produced on passing hydrogen sulphide through 

 a solution of blood. It is formed in putrefaction by the action of this gas 

 which is produced by bacterial action on protein. It was believed to be the 

 cause of the greenish colour of the skin of corpses (Hoppe-Seyler). 



Gamgee did not consider it as a definite compound, but Clarke and 

 Hurtley l believe it to be a distinct substance. The solution is green in thin 

 layers, red in thick layers and shows an absorption band in the green towards 

 the violet end. 



Methaemoglobin. HbO ? 



Solutions of oxyhsemoglobin on exposure to the air become brown 

 in colour and on spectroscopic examination show an absorption band in 

 the red as well as the two bands of oxyhaemoglobin. The substance giv- 

 ing the extra band was called methaemoglobin by Hoppe-Seyler in 1 864. 



Methaemoglobin is produced by the action of numerous substances 

 upon haemoglobin such as nitrates, chlorates, permanganates, hydrogen 

 peroxide, nitrobenzene, pyrogallol, etc. It is most conveniently pre- 

 pared by the action of potassium or sodium ferricyanide, thus : 



A dilute solution of blood is treated with a few drops of a strong solu- 

 tion of potassium ferricyanide. The solution becomes reddish-brown in 

 colour. On examination with a spectroscope, the solution shows an 

 absorption band to the red side of D and the blue end is markedly 

 absorbed. There is also a faint band in the green-blue region. On 

 dilution the two bands of unchanged oxyhaemoglobin may appear. 



The absorption band in the red is most characteristic for methaemo- 

 globin. 



If the solution of methaemoglobin be made faintly alkaline with a few 

 drops of ammonia, alkaline methasmoglobin is formed. The solution is more 

 red in colour and shows two bands between D and E like those of oxyhaemo- 

 globin and a third fainter band to the red side of IX 



Conversion of Methcemoglobin into Hemoglobin and Oxyhcemoglobin. 



Methaemoglobin is converted by reducing agents, e.g. ammonium 

 sulphide, into haemoglobin and on shaking with air oxyhaemoglobin 

 is formed. 



Solutions of methremoglobin may thus be distinguished from solu- 

 tions of haematin. 



*J. Physiol., Vol. 36. 

 16 



