CHAPTER IV. 



BASIC AND ACID PROPERTIES OF PROTEINS. 

 A. Basic Properties. 



IT is now generally recognised that proteins have both basic and acid 

 properties. Most of the evidence in support of this has, however, been 

 obtained from experiments in which relatively large quantities of acids 

 have been used, whereby the protein has probably been to some ex- 

 tent altered and its original deportment towards acids changed. The 

 grounds for this assumption are given on page 37, where the denaturing 

 effect of acid is discussed in detail. 



Ritthausen (416) stated that his preparations of crystallised edestin 

 dissolved to a large extent when washed with water, and this has since 

 been observed by all who have made preparations of this protein. 



From this apparently remarkable fact, that the edestin, originally 

 crystallising from a dilute aqueous solution, dissolves on simply washing 

 with water, one would naturally conclude that the protein had either 

 suffered a serious change in the processes employed in isolating it or 

 that the crystalline preparation consisted of at least two distinct proteins 

 of different solubility. Neither of these suppositions is in fact true, for 

 the behaviour of the preparation is wholly due to the basic properties 

 of the edestin, as will be soon shown. 



A failure to recognise the effect of the basic nature of vegetable 

 proteins on the solubility and other properties of their preparations has 

 led to much of the confusion that still exists in regard to them. Since 

 a clear understanding of these properties is fundamental to an intelli- 

 gent study of the plant proteins, and its importance appears as yet not 

 to be fully appreciated, experiments made by the writer with edestin 

 (312, 315) are here given in considerable detail. 



Pure edestin, from hemp-seed, when free from combined acid or 

 alkali, is entirely insoluble in water, but in the presence of a very little 

 acid, and in the complete absence of salts, it promptly dissolves to a 

 clear solution. From such a solution the edestin is readily precipitated 

 by the addition of a small quantity of a neutral salt, e.g., sodium chloride, 



22 



