3i6 PROTEINS 



drate, glucosamine.* And lastly, a nucleo-protein, when 

 subjected to peptic digestion, or treated with dilute acid, 

 gives a protein and a nuclein ; this latter with caustic 

 alkali breaks up still further into a second protein and a 

 nucleic acid ; the nucleic acids on further hydrolysis yield 

 phosphoric acid, a carbohydrate residue, either a pentose 

 or glucose, and purine bases, such as guanine, adenine, 

 xanthine, etc. These changes are rendered clearer by 

 the following scheme : — 



Nucleo-protein 



\ 



I I 



Protein A Nuclein 



I I 



Protein B Nucleic acid 



I 



Phosphoric Carbo- Purine 



acid hydrate bases 



It must be borne in mind that the protamines and 

 histones frequently occur loosely combined with nucleic 

 acids in the form of salts, but this type of combination is 

 different from that between a protein and a nuclein such 

 as is found in true nucleo-proteins. 



The conjugated proteins appear to be rarely found in 

 plants. 



With regard to the occurrence of nucleo-proteins 

 among plants, it is undoubtedly true that nucleic acid 

 has been repeatedly found in plants, and compounds 

 of proteins with nucleic acid have been isolated by 

 Osborne, but it is not certain whether these substances 

 actually occurred pre-formed in the seed, or were pro- 

 duced during the process of their isolation. Osborne f is 



* Glucosamine is a peculiar nitrogen containing sugar of the formula 



-o- 



I ^ I 

 CH2OHCHOHCHOHCHOHCHNH2CHO or CH2OHCHOHCH -CHOH • CHNH2CHOH 



It has all the ordinary reactions of sugars as regards reduction of Fehling's solu- 

 tion, reaction with phenylhydrazine, etc., but is not fermentable by yeast. Owing 

 to the presence ot the amino group, it is also able to form salts with acids such 

 as hydrochloric acid. It was first obtained by the hydrolysis of chitin contained 

 in the shell of lobsters and has since been obtained by the hydrolysis of several 

 gluco-proteins such as serum mucoid, etc. 



+ Osborne ; " The Vegetable Proteins," London, 1909, 



