Increased inhibition of HGPRT by IMP and GMP and higher levels of PRPP in an 8-azaguanine - hat resistant mutant of Chinese hamster cells.

In this paper an 8-azaguanine resistant mutant of Chinese hamster cells able to grow in HAT medium is analyzed. Kinetic analysis of hypoxanthine-guanine-phosphoribosyl-transferase show that the enzyme of the mutant has an altered affinity for both phosphoribosyl-pyrophosphate and the inhibitors IMP and GMP. Furthermore we show that mutant cells exposed to inhibitors of de novo purine synthesis have increased levels of phosphoribosyl-pyrophosphate probably due to decreased utilization by the de novo pathway. These results explain the ability of the mutant to grow both in 8-azaguanine and HAT medium.