JBC, Vol. 251, Issue 5, 1427-1430, Mar, 1976
Control of pyrimidine biosynthesis in human lymphocytes. Inhibitory effect of guanine and guanosine on induction of enzymes for pyrimidine biosynthesis de novo in phytohemagglutinin-stimulated lymphocytes
K. Ito and H. Uchino
Human peripheral lymphocytes were incubated with Phaseolus vulgaris
phytohemagglutinin. The induction of glutamine-utilizing carbamyl phosphate
synthetase (EC 2.7.2.5) and aspartate transcarbamylase (EC 2.1.3.2) for
pyrimidine biosynthesis de novo and the induction of uridine kinase were
observed as described previously (Ito, K., and Uchino, H. (1971) J. Biol.
Chem. 246, 4060-4065; Ito, K., and Uchino, H. (1973) J. Biol. Chem. 248,
389-392; Lucas, Z.J. (1967) Science 156, 1237-1240). By the addition of 1
mM guanine to the culture, the induction of the former two enzymes was
inhibited, while that of uridine kinase was not, and even accelerated. An
increase in the rate of [14C] bicarbonate incorporation into the
acid-soluble uridine nucleotides via the de novo pathway for pyrimidine
biosynthesis after phytohemagglutinin stimulation was inhibited by guanine,
the incorporation rate being almost at the level of the control culture
without phytohemagglutinin. Guanosine had a similar effect on pyrimidine
biosynthesis. The induction of the three enzymes mentioned above was
completely inhibited by adenine (1 mM). Guanine and guanosine seem to have
a unique inhibitory effect on the induction of glutamine-utilizing carbamyl
phosphate synthetase and aspartate transcarbamylase.
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