26 LABORATORY WORK IN PHYSIOLOGICAL CHEMISTRY. 



CONJUGATE PROTEINS. 



These substances are much more complex in their chem- 

 ical constitution than the simple proteins. They may be 

 subdivided into 



1. The Glycoproteins compounds of a protein component 

 and a carbohydrate complex. 



2. The Nucleoproteins compounds of a protein compo- 

 nent and nucleins or nucleic acids. 



3. The Hcemoglobins and related bodies compounds of 

 a protein component and a pigment which is chiefly respira- 

 tory in character. 



4. The Lecithoproteins compounds of a protein com- 

 ponent with lecithins. 



5. The Phosphoproteins compounds of a protein com- 

 ponent and a phosphorus containing substance other than 

 nucleic acid or lecithins. 



GLYCOPROTEINS. 



In a certain sense some of the simple proteins may be 

 considered as glycoproteins, in that they yield, upon decom- 

 position, reducing substances of undoubted carbohydrate 

 nature; in the case of the true glycoproteins, however, the 

 carbohydrate nucleus is obtained without interference with 

 the integrity of the component protein molecule. The 

 mucins, mucoids, and chondroproteins form the chief classes 

 of the glycoproteins. 



Of the mucins, that obtained from the saliva is selected 

 as a typical example for study. They do not contain phos- 

 phorus, are acid in nature, and are mainly characterized by 

 forming viscous colloidal solutions. The mucins dissolve in 

 weak alkali solutions and may be reprecipitated on the addi- 

 tion of a weak acid. Upon boiling with a dilute acid they split 

 off a carbohydrate nucleus which reduces Fehling's solution. 



