i86 BIOLOGICAL CHEMISTRY 



various steps are inserted. The absence of any one of these 

 enzymes will prevent that stage of the reaction and the 

 appearance of some intermediate product in the urine. Thus 

 the absence of adenase will prevent the conversion of adenine 

 to hypoxanthine, and adenine will appear in the urine. 



The uricolytic enzyme seems to be deficient in man and the 

 higher apes, hence these species excrete a fair amount of 

 uric acid in their urine. Uric acid administered to an animal 

 is partially destroyed and partially excreted unchanged. 



Adenase is absent from the human body, hence adenine in 

 the food passes into the urine, but in the destruction of 

 nucleic acid the adenine is diamidised in a combined state 

 and not set free as adenine. 



In birds and reptiles the main end product of nitrogenous 

 metabolism is uric acid. In these cases the uric acid seems 

 to be synthesised from ammonia and lactic acid, mainly in 

 the liver.* 



In addition to uric acid and other oxy-purines, methyl 

 purines are found in the urine. They are probably derived 

 from the methyl purines caffeine, theophylline and theo- 

 bromine of coffee, tea and cocoa respectively. 



We therefore see that uric acid metabolism is rather 

 complicated. The amount of uric acid excreted depends upon 

 the amount of purine in the food, the amount of nucleo 

 protein destroyed and the activity of the uricolytic enzyme. 

 Pathological conditions upset these various activities and 

 disorders of uric acid metabolism are frequently encountered. 



Uric acid is estimated either by precipitating it as ammonium 

 urate in the presence of excess of ammonium salts : the 

 precipitate being titrated with potassium permanganate in 

 the presence of sulphuric acid f or colorimetrically. 



Creatinine. The amount of this substance is fairly constant, 

 and therefore it depends upon some metabolic factor. If protein 

 food is withheld the amount of urea in the urine is decreased, 

 and as the creatinine remains constant in amount it becomes 

 a larger proportion of the total nitrogenous excretion. 



The importance of creatinine has been shown since Folin 

 introduced a convenient color ime trie method of estimating it. 

 The method consists in comparing the colour produced under 

 standard conditions by the well known Joffe test with picric 

 acid and alkali against a standard colour 4 



* O. Minkowski, Arch.f. exper. Path. u. Pharm., 1886, vol. 21, p. 41. 

 f F. G. Hopkins, Proc. Roy. Soc., 1893, vol. 52, p. 93, and O. 

 Folin and P. A. Shaffer, Zeit. physiol. Chem., 1901, vol. 32, p. 552. 

 J O. Folin, Amer. Journ. Physiol., 1905, vol. 13, p. 48. 



