114 GENERAL BIOCHEMISTRY 



other organic or inorganic structures. I'his major group is then iur- 

 ther subdivided on the basis ol solubility. 



A. Albii)iii)is. Sokible in water and dilute saUs, acids, and alkahs. 

 Coagulated by heat, although there are great variations in sensitivity. 

 Egg albimiin, serum albumin from blood, and many enzymes are ex- 

 amples. 



B. Globulins. Most are insoluble in water but dissolve in salt solu- 

 tions of moderate concentration. Less soluble in concentrated salt solu- 

 tions than albumins. Heat coagulated. Obviously the globulins may 

 grade into the albumins, and the classification is not clear cut. Many 

 seed proteins, myosin from muscle, and the antibodies of blood are 

 typical examples. 



C. Glutelins. Insoluble in water and salt solutions at isoelectric 

 pH values. Dissolve in dilute acids and alkalis. A number of seed 

 proteins, particularly those of cereal grains, are typical examples. 



D. Prolamines. Insoluble in water but dissolve in 70 to 80 per cent 

 ethanol. Have relatively few polar groups, are usually high in proline 

 and amide groups, and are also common in seeds. 



E. Scleroproteins or albnyninoids. Insoluble in all solvents except 

 when coincident with decomposition. Include structural and fibrous 

 proteins. 



F. Histories. Soluble in water but insoluble in dilute ammonia. 

 Biologically associated with certain acidic structures and are them- 

 selves quite basic, being high in lysine and arginine. Examples in- 

 clude globin of hemoglobin and the protein components of most 

 nucleoproteins. 



G. Protamines. Small basic proteins not coagulated by heating and 

 soluble in most aqueous systems. Known only in combination with 

 nucleic acid in the sperm of fish. 



II. Conjugated proteins. Yield other materials than amino acids on 

 hydrolysis. Often the special group may be detached without destruc- 

 tion of the protein moiety, which may then be classified according to 

 Part I above. Many conjugated proteins have quite specific functions. 



A. Phosphoproteins. Contain phosphate groups linked through 

 ester bonds to hydroxyamino acids. Casein and pepsin are typical. 



B. Glycoproteins or mucoids. Conjugated with carbohydrate, usu- 

 ally macromolecular polysaccharides containing acetylglucosamine, 

 other sugars or sugar acids, and sulfate or phosphate esters. Tend to 

 have unusual properties based on the presence of many polar groups. 

 Not much is known about them, but they occur in eggs and blood. 

 The gonadotropic hormone is an example. 



C. Chromoproteins. Possess structures absorbing visible light and 



