522 DIABETES 



(the " D : N ratio ") staying at 3.75 : 1 (Lusk). In pancreat- 

 ectomized dogs the D :N ratio is about 2.8 : 1 during starva- 

 tion (Minkowski). This and other facts seem to indicate that 

 under these conditions sugar is formed from the body proteids. 

 This brings forward the long-contested question as to the possi- 

 bility of : 



THE FORMATION OF SUGAR FROM PROTEIDS 1 



In favor of this source of sugar has long been known the fact that dia- 

 betics, when kept for a long period on carbohydrate-poor diet, excrete 

 sugar in quantities out of all proportion to the amount of carbohy- 

 drate in the food. At the same time the amount of nitrogenous elimi- 

 nation will be found to be excessive, supporting the idea that the sugar 

 of the urine may have been derived from the breaking down of proteids. 

 If the patient is kept for some time on a diet both free from carbohy- 

 drates and poor in proteids, it will be found that the addition of proteid 

 to the diet causes at once an increased elimination of sugar in the urine. 

 Nor is all this sugar derived from the carbohydrate groups of the pro- 

 teid, for, firstly, it may greatly exceed the amount of carbohydrate 

 groups contained in the proteid ; and, secondly, the amount of sugar 

 escaping in the urine does not vary according to the amount of carbo- 

 hydrate in the proteid of the food : e.g., casein is free from carbohydrate 

 groups, but it may cause more increase in glycosuria than does egg-albu- 

 men, which is rich in carbohydrate groups. 2 



It has been demonstrated experimentally that carbohydrates can be 

 formed from the amino-acids of the proteid molecule. If alanin is 

 given to diabetics, it will be found to give rise to almost equivalent quan- 

 tities of sugar ; with normal persons or animals this conversion of alanin 

 into sugar does not seem to occur. Similar, but somewhat less conclu- 

 sive evidence has been obtained that glycocoll and leucin 3 may also be 

 changed into sugar. Feeding of alanin to starved rabbits may cause an 

 increase in the glycogen in the liver ; and starved animals poisoned with 

 phlorhizin excrete more sugar when alanin is given them, 4 



Presumably, therefore, amino-acids liberated from the proteids during 

 their metabolic decomposition can give rise to carbohydrates. The steps 

 by which alanin might be changed into dextrose are as follows : 



CH 3 

 Alanin is amino-propionic acid, CH NH 2 , and by substitution of 



COOH 



an OH group for the NH 2 group, a process that may readily occur in 

 the body through the action of deamidizing enzymes (amidase), it is 



1 Literature by Langstein, Ergebnisse der PhysioL, 1902 (Bd. 1, Abt. 1), 63 ; 

 1904 (Bd. 3, Abt. 1), 453; Therman, Skand. Arch. f. Physiol., 1905 (17), 1. 



2 See Therman, loc. cit. 



3 Mohr (Zeit. exp. Path. u. Then, 1906 (2), 463) has noted the elimination 

 of leucin fed to diabetics, in the form of a polypeptid. 



*See Almagia and Embden, Hofmeister's Beitr., 1905 (7), 298. 



