PKOTEINS 279 



Conjugated Proteins 



These compounds are made up of protein combined with some 

 other substance or substances. The non-protein portion is called 

 the prosthetic group : 



Glycoproteins. These proteins are characterized by a high 

 content of a carbohydrate derivative, usually glucosamine. They 

 usually are divided into two groups, mucoids from the tissues 

 and mucins from the fluids and secretions of the body. As these 

 substances are extremely difficult to purify even approximately, 

 there is much disagreement as to their composition and prop- 

 erties. 



31. Mucoids or CJiondroproteins. The mucoid obtained by 

 extracting the ligament and tendon in the preparation of albu- 

 minoids may be studied if time permits. The mucoid is precipi- 

 tated by acidifying with acetic acid. It gives the usual protein 

 color tests. By hydrolizing with 10% HC1 it may be split up. 

 Sulphate and carbohydrate may be detected in the hydrolyzed 

 liquid. 



Mucin. 



32. Rinse the mouth carefully with distilled water, and collect 

 a test tube of saliva. If there appear to be solid particles in the 

 liquid it should be filtered. Add 10% acetic acid as long as a 

 precipitate forms. This precipitate is mucin. It is not soluble 

 in excess of the acid. Allow to settle, decant most of the liquid, 

 and if the precipitate is sufficiently heavy, filter and use small 

 portions of the residue for the following tests. If the precipitate 

 is very slight, use portions of the saliva containing the pre- 

 cipitated mucin from which most of the clear supernatant liquid 

 has been poured off. 



33. On a portion of the mucin suspended in water try the 

 biuret and the xanthoproteic tests. 



34. Hydrolyze a portion of the mucin by boiling with dilute 

 HC1, and, with portions of the liquid, test for sulphate, and for 

 carbohydrate. 



Hemoglobins. The hemoglobins are compounds consisting 



