HYDROLYSIS 



I. HYDROLYSIS. 



The complex problem of the composition of the protein molecule 

 has been solved by the method of hydrolysis, though other methods 

 such as fusion with alkali, oxidation with permanganate, chromic acid, 

 etc., action of halogens have been employed. Hydrolysis has been 

 effected by (i) boiling with acids, (2) boiling with alkalies, (3) the 

 action of the various proteoclastic enzymes which occur in animals 

 and plants. Proteins were first hydrolysed by acids in 1820 by 

 Braconnot, who used dilute sulphuric acid; between 1850 and 1875 

 hydrochloric acid was most frequently used as the hydrolysing agent 

 by Ritthausen, Hlasiwetz and Habermann, and others; from 1870 

 to 1880 Schiitzenberger employed baryta water under pressure. The 

 action of vegetable enzymes on proteins was studied chiefly by 

 Schulze and his co-workers, that of animal enzymes by Kiihne, 

 Kossel, Kutscher, Drechsel, and numerous other investigators. 



(a) Hydrolysis with Hydrochloric Acid. 



(i) Concentrated Acid. 



Hydrolysis of proteins by boiling with concentrated hydrochloric 

 acid for several hours produces a dark brown solution of the products. 

 Hlasiwetz and Habermann [1871, 1873] carried out the hydrolysis in 

 the presence of stannous chloride in order that the solution should 

 remain colourless. This addition is not necessary, as was shown by 

 Cohn [1896-97] and was not made by E. Fischer in his researches. 



The hydrolysis of protein is usually carried out by heating it with 

 three times its quantity of concentrated hydrochloric acid of specific 

 gravity 1*19. The protein is placed in a round flask and covered with 

 the acid ; on shaking and warming slightly it gradually passes into 

 solution. The solution, which at first may become violet in colour, 

 gradually turns brown ; it is then boiled under a reflux condenser for 

 six to twenty-four hours, depending on the particular protein. The 

 solution has finally a dark brown colour and during the hydrolysis a 

 portion of the hydrochloric acid is evolved as gas. It is filtered from 

 humin substances (secondary products arising from carbohydrate and 

 tryptophan and other units, see p. 65) and fatty material by passage 

 through a Buchner funnel covered with linen, and these are well washed 

 with water. The products are isolated from this solution. 



