De novo purine biosynthesis has been studied in lymphocyte cell lines 
established from Lesch-Nyhan patients deficient in hypoxanthine-guanine 
phosphoribosyltransferase (HGPRT), in in vitro differentiating erythroleukaemic 
cell lines cloned from cells charactistic of virus-induced murine leukaemia, and 
in mutant hamster cells deficient in amidophosphoribosyltransferase. The 
relationship between cellular phosphoribosylpyrophosphate (PP-ribose-P) 
metabolism and the activity of the enzymes which catalyse the early steps of de 
novo purine biosynthesis has been explored. It was found that hamster cells 
deficient in amidophosphoribosyltransferase did not accumulate PP-ribose-P as do 
HGPRT-deficient cells. In these model systems, an accelerated rate of de novo 
purine biosynthesis tended to be associated with an increase in cellular 
PP-ribose-P cotent, but decreases in this rate results from the reduction in the 
activity of amidophosphoribosyltransferase. Regulation of ammonia-dependent de 
novo purine biosynthesis was similar to that of glutamine-dependent purine 
biosynthesis.