106 BIOLOGICAL CHEMISTRY 



We shall first of all examine the metabolism of carbohydrates 

 and then that of fats and proteins ; finally we must look for 

 substances which may be intermediate links for the inter- 

 conversion of carbohydrates, fats and proteins. 



METABOLISM OF CARBOHYDRATES 



By hydrolysis all carbohydrates yield glucose in the body, 

 hence we must study the decomposition of glucose. The 

 earliest observations were those of Wiedemann* and of 

 Schmiedeberg and Meyer, f who found that when camphor 

 was administered to animals its poisonous action was neutral- 

 ised by combining it with glucuronic acid. The glucuronic 

 acid was presumed to be the first oxidation product of glucose. 

 After starvation, when the carbohydrate stores have been 

 depleted, less camphor can be neutralised, but if glucose 

 is given along with the camphor the toxic action of the camphor 

 is more readily withstood. The further stages of decomposition 

 should lead to the formation of ^-saccharic acid, oxalic acid, 

 carbon dioxide and water, but the experimental evidence is 

 not in favour of this chain of oxidation products. It appears 

 probable that glucose can give rise to glucuronic acid, but 

 that under normal conditions a very small proportion of the 

 sugar oxidised passes through the stage of glucuronic acid. 



The main line of glucose destruction seems to lead to the 

 formation of lactic acid, one molecule of glucose giving rise 

 to two molecules of lactic acid. The intermediate products 

 are possibly glyceric aldehyde or dihydroxy acetone. The 

 formation of lactic acid from glucose is not improbable from 

 the chemical point of view, as the various stages can be 

 imitated outside the body. Glucose, when acted upon by 

 alkali, yields pyruvic aldehyde and pyruvic aldehyde on 

 treatment with alkali yields lactic acid. Glyceric aldehyde 

 and di-hydroxy acetone yield lactic acid after treatment 

 with alkali. Dakin and Dudley have recently found an 

 enzyme glyoxalase which can convert pyruvic aldehyde into 

 lactic acid.J 



The formation of lactic acid explains the increase in acidity 

 so frequently found in tissues during activity. Muscle, for 

 instance, in the resting condition contains no lactic acid, 

 but during activity lactic acid is formed. The removal of 



* Wiedemann, Arch. f. exper. Path. u. Pharm., 1877, vol. 6, p. 216. 



f O. Schmiedeberg and H. Meyer, Zeit. f. physiol. Chem., 1879, vol. 

 3, p. 422. 



J H. D. Dakin and W. H. Dudley, Joum. BioL Chem., 1913, vol. 

 M. P-*555- 



