Nitrogen excretion and the formation of uric acid

Subsequent studies suggested that avian liver might contain small amounts of arginase. Brown (1966) made a comprehensive study of arginase activity in avian livers (Table 5.1) and was able to detect it in all species studied. He attributes dementi s failure to detect activity to the lower sensitivity of the methods then available and to suboptimal 

The incorporation of ammonia into urea or into uric add requires both energy and building blocks. The synthesis of uric acid is more costly in both ATP and 

Component High-protein diet Low-protein diet 

In this way, the nitrogen from several amino adds can be transferred to aspartate, glutamate or glutamine The ketoacid acceptors may originate from glucose or gluconeogenic precursors. The C-1 atom on formyltetrahydrofolate may arise from serine or methionine. In addition HC07 is required for the carboxylation of 5 -phosphoribosyl-5-aminoimidazole. 

The importance of the avian liver in the synthesis of uric acid became dear as the result of two early experiments (see Baldwin, 1967). When geese were hepatectomised, there was a rapid rise in the concentration of ammonia in the blood and when goose liver was perfused with ammonia, the formation of uric acid could be detected. The biosynthetic pathway leading to uric add formation shares many of the enzymes required for the purine precursors of the purine nucleotides. The three steps that are distinct for uric acid formation are the conversion of 

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