THE INDIVIDUAL GROUPS OF PROTEINS 493 



Oxyhaemoglobin crystals dissolve more or less readily in water according 

 to the blood from which they have been prepared ; they also dissolve in 

 dilute alcohol, but are insoluble in ether, chloroform, benzene and most other 

 organic solvents. 



Dilute aqueous solutions are more stable than concentrated ones and 

 solutions containing a few drops of alkali carbonate are more stable than 

 neutral solutions. 



Solutions of oxyhaemoglobin show the colour reactions for proteins but 

 the reactions" are more or less masked by the pigment. They coagulate on 

 heating and are precipitated by alcohol and strong acids. Decomposition 

 into haematin and globlin occurs. They are not precipitated by lead acetate, 

 but they are precipitated by solutions of the alkaloidal reagents in acid solution. 



Solutions of oxyhsemoglobin are dextrorotatory (+ 10 for a 1*2 per cent, 

 solution). 



Haemoglobin. 



Crystals of haemoglobin are obtained in the same way as those of 

 oxyhaemoglobin after the blood has been reduced by exposure to a vacuum, 

 with Stokes' reagent or other reagents. 



Haemoglobin crystals separate if blood be kept in a sealed vessel. 



Crystals of haemoglobin are dark red in colour, usually isomorphous with 

 those of oxyhaemoglobin. They are more easily soluble in water and on ex- 

 posure to the air absorb oxygen changing into oxyhaemoglobin. Haemoglobin 

 is decomposed by acids and alkalies in the absence of oxygen into haemo- 

 chromogen and globin. 



Carboxyhaemoglobin. 



Carbon monoxide is passed through a concentrated solution of oxyhaemo- 

 globin and the solution is treated as described under oxyhsemoglobin. 



Crystals of carboxyhaemoglobin resemble those of oxyhaemoglobin and dis- 

 solve in water with a carmine-red colour, i gm. of carboxyhasmoglobin con- 

 tains i '34 c.c. of CO at o and 760 mm. (Hiifner). It is more stable than 

 oxyhaemoglobin, but the carbon monoxide can be removed by exposure to a 

 vacuum or passing oxygen through its solution. It also loses carbon monoxide 

 slowly on standing in the air and is converted into oxy- and methaemoglobin. 

 It is converted into methaemoglobin by the action of potassium ferricyanide 

 (Haldane). 



It shows a spectrum very similar to that of oxyhaemoglobin. Its solutions 

 on heating give a pale red coagulum, due to decomposition into carboxy- 

 haemochromogen and protein. It becomes darker in the air due to the forma- 

 tion of haematin. 



Nitric Oxide Haemoglobin. 



Nitric oxide is passed into a solution of carboxyhaemoglobin crystals or 

 a solution of methaemoglobin is shaken with nitric oxide. The solution by 

 treatment as described under oxyhaemoglobin -yields crystals of nitric oxide 

 haemoglobin. 



The crystals of nitric oxide haemoglobin are similar to those of oxyhaemo- 

 globin and their spectrum is almost identical with that of oxyhaemoglobin. 



M ethaemoglobin. 



A concentrated solution of oxyhaemoglobin of pig's, horse's, or dog's 

 blood is treated with 10 per cent, potassium ferricyanide solution until it is 

 of a dark brown colour, cooled to o and ice-cold alcohol added as in the 

 preparation of oxyhaemoglobin. Crystals separate out on standing at o. 



The crystals of methaemoglobin which have been obtained are slender 

 needles of a reddish-brown colour, easily soluble in water. The solution in 

 water and acids is red-brown in colour, in alkali red. The solution is pre- 

 cipitated by lead acetate or basic lead acetate. 



Tne spectrum of the solution shows one band in the red, 



