FORMATION OF SUGAR FROM PROTEIN 233 



FORMATION OF SUGAR FROM PROTEIN 



Coming next to one of the great fundamental problems 

 of the study of metabolism, one upon which biologists from 

 the olden times of Claude Bernard to the present have time 

 and again tested their acumen, we have to consider the 

 question of the formation of sugar from protein. 



Carbohydrate Group in Protein Molecule. Long after 

 the possibility of separation of a reducing compound from 

 mucinous substances was known, the discovery that a carbo- 

 hydrate group is a natural component of the proteins was 

 made by Pavy. Friedrich v. Miiller, the clinician, and his 

 pupils contributed mainly to establish the fact that protein 

 sugar is not identical with glucose or any of the other typi- 

 cal hexoses, but is rather an amidized sugar, glucosamine, 

 CH 2 (OH) - CH(OH) - CH(OH) - CH(OH) - CH(NH 2 ) - 

 COH, obtained also by Ledderhose by cleavage of chitin. 36 

 While mucins and many mucoids (as the egg envelopes of 

 the frog and of cephalopods) 37 are about one-third made up 

 of glycosamine, and the amount of this material in ovalbu- 

 min, which is especially rich in sugar, is commonly estimated 

 at about ten per cent., in other true proteids a low percentage 

 or only a fraction of one per cent, is present. Many, as case- 

 in, contain no carbohydrate at all. (It is not difficult to de- 

 termine the amount of carbohydrate of a protein if the latter 

 is hydrolyzed by boiling with a mineral acid, by separating 

 from the mixture the substances which can be precipitated 

 by phosphotungstic acid, and estimating the amount of sugar 

 in the filtrate in the usual manner.) The expectation of 

 finding in the carbohydrate group of the protein molecule 

 the key to the problem of forming sugar from protein soon 

 proved fruitless. We were forced to recognize very soon 

 that the quantity of proteid sugar cannot by any means 



88 Literature upon the Carbohydrate Group in Protein : L. Langstein, 

 Ergebn. d. Physiol., 1', 77-99, 1902; 3', 456-467, 1904; 0. Cohnheim, Chemie der 

 Eiweisskorper, 4th ed., 82-89, 1911. 



37 0. v. Fiirth (F. Hofmeister's Lab., Strassburg, and Zoological Station at 

 Naples), Hofmeister's Beitr., 1, 252, 1901. 



