Abstract
Uricotelic animals use synthesis of the purine ring system as the pathway for excretion of excess nitrogen. This results in a high level of de novo purine synthesis (1). When birds are subjected to stress situations that lead to higher nitrogen excretion, the rate of purine synthesis is increased (2,3) and changes in levels of adenylosuccinate lyase, xanthine dehydrogenase and amidophosphoribosyltransferase occur (2,4). Livers from chickens treated with β-estradiol can provide a model system for a rapidly growing, normal cell. Treatment with this hormone causes a rapid increase in liver weight and in protein, RNA and DNA content in preparation for the production of egg proteins (5). Weber and coworkers (6–8) have shown that the level of certain purine biosynthetic enzymes is increased in regenerating rat liver, another system that is used as a model for normal, rapid growth. This is also true in certain rat liver hepatomas (6–8). The chick liver can therefore be used as a model for study of regulation of purine biosynthesis under conditions where requirements for nucleotides vary.
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