242 PHYSIOLOGICAL CHEMISTRY 



It is easily split off from hemoglobin by the action of dilute hydro- 

 chloric acid. 



The histones give the biuret test, usually only a faint Millon 

 reaction, are precipitated from neutral solution by alkaloidal 

 reagents, and form precipitates if added to a protein solution. 

 They are acted on by the digestive juices. They contain a high 

 percentage of diamino acids. 



7. Protamines. The protamines have been found only in 

 the spermatozoa of fish. The protamines give the biuret test, but 

 most of them give no Millon 's reaction. They are precipitated 

 by alkaloidal reagents, and fairly well by neutral salts. They 

 give precipitates with ammoniacal protein solutions. 



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 : 



1. 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 tis- 

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

 these substances are extremely difficult to purify even approxi- 

 mately, there is much disagreement as to their composition and 

 properties. 



(a) Mucoids or Chondroproteins. 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. 



(b) Mucin. 



i. 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 



