PROTEINS 113 



cule with a substance or substances containing a carbohydrate group 

 other than a nucleic acid. The glycoproteins yield, upon decomposition, 

 protein and carbohydrate derivatives, notably glucosamine, CH 2 OH.- 

 (CHOH) 3 .CH(NH 2 ).CHO, and galactosamine, OHCH 2 .(CHOH) 3 .CH- 

 (XHo).CHO. The principal glycoproteins are mucoids, mucins, and 

 chondro proteins. By the term mucoid we may in general designate 

 those glycoproteins which occur in tissues, such as tendomucoid from 

 tendinous tissue and osseomucoid from bone. (For the preparation of 

 tendomucoid see Chapter XVIII.) The elementary composition of 

 these typical mucoids is as follows: 



N. S. C. H. O. 



Tendomucoid 1 ii-75 2.33 48.76 6.53 30.60 



Osseomucoid 2 12.22 2.32 47 43 6.63 31.40 



The term mucins may be said in general to include those forms of glyco- 

 proteins which occur in the secretions and fluids of the body (For the 

 preparation of salivary mucin see Chapter III.) Chondroproteins are 

 so named because chondromucoid, the principal member of the group, 

 is derived from cartilage (chondrigen) . A myloid* which appears patho- 

 logically in the spleen, liver, and kidneys, is also a chondroprotein. 



The phospho proteins are considered to be " compounds of the 

 protein molecule and some, as yet undefined, phosphorus-containing 

 substances other than a nucleic acid or lecithin." The percentage of 

 phosphorus in phosphoproteins is very similar to that in nucleoproteins, 

 but they differ from this latter class of proteins in that they do not 

 yield any purine bases upon hydrolytic cleavage. Two of the common 

 phosphoproteins are the casein of milk and the ovovitellin of the egg- 

 yolk. The phosphorus in these, as in all proteins, exists in phosphoric 

 acid radicals. For the preparation of a typical phosphoprotein (casein) 

 see Chapter XVII. 



The hemoglobins (chromoproteins) are compounds of the protein 

 molecule with hematin or some similar substance. The principal mem- 

 ber of the group is the hemoglobin of the blood. Upon hydrolytic cleav- 

 age this hemoglobin yields a protein termed globin and a coloring matter 

 termed hemochromogen. The latter substance contains iron and upon 

 coming into contact with oxygen is oxidized to form hematin. Hemo- 

 cyanin, another member of the class of hemoglobins, occurs in the blood 

 of certain invertebrates, notably cephalopods, gasteropods, and 



1 Chittenden and Gies: Jour. Exp. Med., i, 186, 1896. 



2 Hawk and Gies: Amer. Jour. Physiol., 5, 387, 1901. 



3 Not to be confused with the substance amyloid which may be formed from cellulose 

 (see p. 49). 



