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J Bacteriol. 1968 April; 95(4): 1314-1321
Copyright © 1968 American Society for Microbiology. All Rights Reserved.

Effect of Folinate on Thymidine Uptake by Pediococcus cerevisiae1

Frederika Mandelbaum-Shavit and Nathan Grossowicz

a Department of Bacteriology, The Hebrew University-Hadassah Medical School, Jerusalem, Israel

ABSTRACT

Uptake of 3H-thymidine by resting cells of Pediococcus cerevisiae was found to be energy- and temperature-dependent. The pH optimum was between 6.5 and 8.0, and after 2 min of incubation most of the radioactivity was found in the deoxyribonucleic acid (DNA) fraction. Iodoacetate at a concentration of 10–2M caused a 50% inhibition of uptake. Preincubation of resting cells for 10 min with folinate (10–3µ mole/ml) diminished the 3H-thymidine uptake by 75%. In growing cells, the folinate-induced inhibition was still more striking. Deoxyuridine augmented the folinate effect, whereas fluorodeoxyuridine and aminopterin or amethopterin abolished it. Preincubation with folinate did not interfere with the uptake of 3H-amethopterin, and thus the inhibitor did not compete for uptake sites within the cell. The role of these inhibitors in reversing the folinate effect is discussed. Cells preincubated with folinate showed an increased incorporation of 14C-uracil into DNA, presumably after prior conversion to thymidylate. We concluded that the folinate effect was due to stimulation of de novo thymidylate synthesis with concomitant inhibition of the uptake of external thymidine.

FOOTNOTES

1 Part of Ph.D. Thesis submitted to the Hebrew University, Jerusalem, by the senior author.

J Bacteriol. 1968 April; 95(4): 1314-1321
Copyright © 1968 American Society for Microbiology. All Rights Reserved.





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