470 PROTOPLASM 



D. Albumins — white of egg 



E. Glutelins — glutenin from wheat 



F. Prolamins — gliadin from wheat 



G. Scleroproteins — keratin from hair, gelatin from bones 

 H. Phosphoproteins — casein from milk 



II. Conjugated proteins — These are compounds of simple proteins with 

 some other nonprotein group, the union with the nonprotein molecule 

 being otherwise than as a salt 



A. Chromoproteins (hemoglobins) — proteins of wool and hair; the 



nonprotein group is a pigment 



B. Nucleoproteins — proteins of cell nuclei; the nonprotein group is 



nucleic acid 



C. Glucoproteins — mucin from the salivary glands; the nonprotein 



group is a carbohydrate radical 

 III. Hydrolyzed proteins (protein derivatives) — This is an artificial group 

 and includes the various decomposition products of the naturally 

 occurring proteins. 



A. Metaproteins — acid and alkali albuminate 



B. Proteoses — partial hydrolytic decomposition products of proteins 



(precipitated by ammonium sulphate) 



C. Peptones — partial hydrolytic decomposition products of proteins 



(not precipitated by ammonium sulphate) 



D. Polypeptides — compounds of two or more amino acids 



The phosphoproteins have, as the name indicates, a nonprotein 

 group containing phosphorus, yet in the Enghsh classification 

 they are put under simple proteins. 



Atomic Constituents. — All proteins contain carbon, hydrogen, 

 oxygen, and nitrogen; and all, except the protamines, histones, 

 and their derivatives, contain sulphur. These elements may 

 occur in proteins in the following elementary proportions: 

 carbon, 51.55 per cent; hydrogen, 7 per cent; oxygen, 20 to 

 30 per cent; nitrogen, 15.17 per cent; sulphur, 0.4 to 2.5 per cent, 

 from which a formula such as C726H1174N194S3O214 for globin, 

 the basis of hemoglobin, can be calculated. Iron and magnesium 

 are other common protein constituents. The phosphoproteins 

 and nucleoproteins contain phosphorus. The accessory ele- 

 ments sulphur, iron, magnesium, phosphorus, etc., do not always 

 occur as a direct part of the protein molecule but are combined 

 with atomic groups to form definite chemical substances which 

 are more or less firmly bound to the purely protein constituents of 

 the larger complex which we call a protein molecule. Phosphorus 

 in the phosphoproteins is probably combined directly with one 

 of the constituents of the protein molecule, but in the nucleo- 



