THE PROTEINS 7 



B. Conjugated Proteins 



Nudeoproteins are compounds of one or more 

 protein molecules united with nucleic acid. The 

 nucleoproteins, as their name implies, are the proteins 

 of cell nuclei and give to the latter their character. 

 The nucleoproteins are therefore found in largest 

 quantity wherever cellular material is abundant, as 

 in glandular tissues and organs. By artificial hydroly- 

 sis or during treatment in the alimentary tract a nucleo- 

 protein is decomposed into protein and nucleic acid. 

 Nucleic acid, of which there are several types, may 

 be made to yield a series of well-defined compounds, 

 the purine bases (xanthine, hypoxanthine, adenine and 

 guanine), the pyrimidine bases (uracile, cytosine and 

 thymine), a carbohydrate group (pentose or hexose) 

 and phosphoric acid. 



Glucoproteins are compounds of the protein mole- 

 cule with a substance or substances containing a car- 

 bohydrate group other than a nucleic acid. Particu- 

 larly rich in glucoproteins are the mucus-yielding 

 portions of tissues. They serve also as a cement sub- 

 stance in holding together the fibers in tendons and 

 ligaments. An amino-sugar, glucosamine, has been 

 isolated from some of the glucoproteins and it is gen- 

 erally regarded as constituting the carbohydrate radicle 

 of these conjugated proteins. 



Phosphoproteins are compounds of the protein 

 molecule with some, as yet undefined, phosphorus- 

 containing, group other than a nucleic acid or lecithin. 



