Dual effects of ammonium chloride on purine biosynthesis de novo in ehrlich ascites-tumor cells in vitro

Abstract

The effects of NH 4Cl on the first steps in purine biosynthesis de novo in Ehrlich ascites-tumor cells in vitro have been studied to explore the possibility that a postulated non-enzymatic NH 3-utilizing reaction for the synthesis of phosphoribosylamine exists in these cells in addition to the glutamine-utilizing phosphoribosyl pyrophosphate amidotransferase (ribosylamine-5-phosphate: pyrophosphate phosphoribosyl transferase (glutamate-amidating), EC 2.4.2.14) reaction. The addition of NH 4Cl to tumor cells stimulated the first reactions in purine biosynthesis de novo. This stimulation was shown to be due to an increased intracellular concentration of glutamine, and was reduced by feedback inhibition to the same extent as was synthesis de novo of purine stimulated by glutamine. NH 4Cl also inhibited the stimulation of this process usually elicited by glutamine. This inhibition was shown not to be due to non-specific toxicity or to changes in the uptake or metabolism of glutamine by the cells. It is concluded that both the stimulation of purine biosynthesis de novo by NH 4Cl and its inhibition of glutamine stimulation of this process can be explained on the basis of the interaction of NH 3 or NH 4+ with phosphoribosyl pyrophosphate amidotransferase. No evidence for a non-enzymatic NH 3-utilizing reaction was obtained, but one may occur under different conditions.