STUDIES IN PLANT RESPIRATION AND PHOTOSYNTHESIS. 



17 



dog is given glycocoll, there is no oxidation of this material, the energy- 

 content of the glycocoll is eliminated in the urine as glucose and urea, 

 nevertheless the metabolism is greatly increased. When corre- 

 sponding or even larger quantities of glucose are given there is no 

 stimulation of metabolism. From this it follows that the immediate 

 cause of the specific dynamic action is not in the oxidation of the 

 amino-acids and liberation of energy therefrom, but that the amino- 

 acids in some manner stimulate the activity of the cells and thus 

 cause them to metabolize more food material. 



The specific dynamic action of proteins, especially with the insight 

 gained through Lusk's investigations, throws considerable light on 

 the general problem of the function of amino-acids in energesis. 

 It does not, however, enlighten us on the fundamental causes of this 

 stimulating action of the amino-acids. 



Our first inclination was to search for a purely chemical explanation 

 which could account for this remarkable behavior. A natural 

 supposition seemed to be that the amino-acids affected the sugars in 

 such a manner as to make them more easily broken down and oxi- 

 dized. As Nef^ has shown, glucose is a relatively stable sugar, 

 while fructose is more completely oxidized. Thus, in order to reduce 

 completely a mixture of 382.5 grams CUSO4 and 163.8 grams NaOH 

 (Fehling's solution), the amounts of the various sugars shown in 

 table 6 were required: 



Table 6. 



Similarly, Lusk^ demonstrated that fructose was metabolized 

 more actively than glucose, so that the percentage of increase over 

 the indirect basal metabolism for the various sugars was found to be : 

 glucose 30, fructose 37, sucros6 34, galactose 22, and lactose 3. 

 In view of these facts it was possible that the amino-acids acted as 

 isomerizing agents, converting the glucose into the more active 

 fructose, just as had been shown to happen with a great variety 

 of substances, e. g., Ca(0H)2, Pb(0H)2, NaaCOs, etc.^ All of our 

 experiments directed to estabHsh such an isomerizing action of the 

 amino-acids on various hexose sugars yielded negative results. 



1 Nep, J. U. Annalen der Chemie (Leibig), 357, 219 (1908). 



« LuBK, Graham. Jour. Biol. Chem., 20, 656 (1915). 



» Nef, J. U. Annalen der Chemie (Liebig), 357, 294-312 (1908); 403, 240-383 (1914). 



