CHAPTER VII. 



DENATURING OF VEGETABLE PROTEINS. 

 A. Denaturing by Acids. 



PROTEINS are subject to changes whereby their molecules are slightly 

 altered and their solubility is changed. Our knowledge of the nature 

 of these changes and the various products which result from the dena- 

 turing influence of the agents which bring them about, is very limited. 

 It is commonly stated that the action of acids on proteins produces 

 "acid albumin," which is described as insoluble in water but readily 

 soluble in the slightest excess of either acid or alkali. Products of such 

 solubility appear to be formed by the action of acid on nearly all kinds 

 of proteins, and the " acid albumin " which results corresponds in its 

 constitution with the protein from which it originated, for the changes 

 involved in its formation are slight and do not lead to any profound 

 decomposition of the protein molecule. Little attention appears to 

 have been paid to the possibility of the formation of intermediate pro- 

 ducts between the native protein and this " acid albumin," and much 

 confusion exists in the literature in connection with the action of acids 

 on proteins. The only attempt known to the writer that has yet been 

 made to study this question is one made by him some years ago (314, 

 311), in which the effect of small quantities of acid on edestin was 

 studied with some care. As the results of these experiments appear 

 to have a general application and to shed considerable light on the 

 denaturing effect of acids on proteins they will here be described in 

 detail. 



Crystallised edestin, when dissolved by the least possible quantity 

 of hydrochloric acid, yields a solution which is precipitated by the ad- 

 dition of a little sodium chloride. This precipitate when treated with 

 a strong solution of sodium chloride never wholly redissolves. If the 

 part that does dissolve is recrystallised and the experiment repeated, a 

 part of the preparation originally soluble in a neutral salt solution 

 again remains undissolved, and this occurs each time the experiment 

 is tried. This insoluble derivative, which cannot be made soluble 



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