THE PROTEINS 373 



The a and ft protoproteoses are very similar to one another and are easily 

 soluble in water. Heteroproteose is very little soluble in water and can be 

 separated from the others by dialysis ; it is precipitated from solution. 



Heteroproteose and the protoproteoses are more easily separated by 

 means of alcohol. Heteroproteose is precipitated by 32 per cent, of alcohol ; 

 protoproteose is soluble in alcohol up to 80 per cent. 



If an equal volume of alcohol be added to the above solution of primary 

 proteoses, the heteroproteose will be precipitated. 



(2) Secondary or Deuteroproteoses. 



These proteoses are precipitated by complete saturation of the 

 solution of proteoses and peptone with ammonium sulphate. The 

 filtrate remaining after the precipitation of the primary proteoses is 

 acidified with a drop of dilute sulphuric acid and saturated with finely 

 powdered ammonium sulphate. 1 A flocculent precipitate comes down 

 and is filtered off. 



If it be dissolved in water, it will be found not to give all the above 

 reactions for proteoses, e.g. : 



The reactions with acetic acid and potassium ferrocyanide, con- 

 centrated nitric acid, copper sulphate are negative. 



This precipitate also consists of a mixture of at least two deuteroproteoses, 

 a and /?, and a third has been described. They differ in their behaviour 

 towards ammonium sulphate. 



Both the primary and secondary proteoses are very indefinite substances 

 and methods have still to be devised for a perfect separation. 



PEPTONE. 



Peptone is not precipitated by saturation with ammonium sulphate. 

 It therefore remains in solution after the proteoses have been removed. 



Its chief characteristic is the biuret reaction : 



A portion of the filtrate is treated with excess of strong caustic 

 soda solution (40 per cent, or solid substance) and a drop or two of 

 I per cent, copper sulphate solution. A pink colour appears, which is 

 .characteristic of peptone. It is necessary to add a large excess of 

 caustic soda if ammonium sulphate be present in the solution in order 

 to decompose it and in order that the alkalinity should be due to sodium 

 hydroxide ; the alkalinity of ammonia does not produce the colour. 



Of the other colour reactions they are sometimes positive, some- 

 times negative, depending on the peptone. 



Peptone is precipitated by some of the precipitating reagents, e.g. 

 tannic acid, phosphotungstic acid, lead acetate, but not by others. 



Peptone again is a mixture which has not been perfectly separated ; 

 at least two peptones are present. 



1 4 gm. to every 10 c.c. of half saturated solution. 



