LECTURE XIII. 

 THE NUCLEOPROTEIDS AND THEIR CLEAVAGE-PRODUCTS. 



IN discussing the proteins, we have only briefly referred to those which 

 do not occur by themselves, in the tissues, but are united to a second 

 atomic complex. To these compound proteins, also called proteids, belong 

 the nucleoproteids. They occupy an important position, not only in animal 

 economy, but in that of the plant cell as well. They are widely distrib- 

 uted, and are mainly found in the nuclei of cells. It is at present very 

 difficult to decide whether the materials classified under the name of 

 nucleoproteids are of an individual nature, within certain limits. They 

 are purified with difficulty, and are mainly characterized by their cleavage- 

 products. From what we know, it appears that the albuminous compo- 

 nent may vary widely in character. For example, we find histones and 

 varieties of protamines. The other component, which we shall shortly 

 consider, also shows differences in composition according to the nature 

 and derivation of the nucleoproteid. When we recollect all that has been 

 said regarding this class of substances, we are involuntarily forced to the 

 conclusion that an exact decision as to the construction of the nucleo- 

 proteids is not possible, largely because it is certain that these proteids are 

 obtained in various degrees of purity, according to the method used for iso- 

 lating them ; or, perhaps better expressed, because in certain investigations 

 products have been worked with which had already undergone considerable 

 change. The albumin component shows all the characteristics common to 

 the proteins. Above all, it possesses the property of " denaturizing," which 

 often serves to impart an entirely new property to an isolated product, 

 thus apparently indicating a new compound. We are forced to obtain 

 the nucleoproteids from the cells themselves, i.e., from a very complex 

 mixture of proteins. The fact that in the different nucleoproteids the 

 two components are combined with different degrees of firmness, may 

 likewise lead to errors, and prevents, more than anything else, any energetic 

 attack in the attempt to purify the isolated products. 



When we take all these facts into consideration, there is little wonder 

 that the existence of the nucleoproteids should be repeatedly questioned. 

 We have to thank F. Miescher for much of our knowledge about these 

 bodies. The non-albuminous component, nucleic acid, will precipitate 

 albumin. It is conceivable that it shows its precipitating power during 

 the isolation of the proteids, and is thus brought to our attention as 



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