Molecular Pharmacology, Vol 3, 537-548, Copyright © 1967 by the American Society for Pharmacology and Experimental Therapeutics

Interference of Barbiturates with Pyrimidine Incorporation

I. Amobarbital Inhibition of Orotate Uptake into Bacillus cereus

¹ Department of Pharmacology, The George Washington University School of medicine, Washington, D. C. 20005

Amobarbital, 10^-3M, inhibited the conversion of orotate-2-¹⁴C into RNA pyrimidines of exponentially growing Bacillus cereus. The drug produced no effect on the growth rate or oxygen uptake of time cells. Furthermore, the incorporation of adenine or uracil into polynucleotides, of amino acids into protein, and of diaminopimelate into cell wall was unaltered by amobarbital.

The effect on orotate incorporation was detectable at 10^-4 M amobarbital, increased with higher concentrations of the barbiturate, amid decreased as the concentration of orotate in the medium was raised.

Studies to localize the effect eliminated the conversion to DNA, the interconversion of RNA pyrimidines, the decarboxylation of orotate, the de novo biosynthesis of pyrimidines, and the flavin-mediated interconversion of orotate and dihydroorotate as the drug-sensitive step. It is concluded that amobarbital, probably as the undissociated compound, markedly depressed the uptake of orotate into the cells. Time otherwise unaffected conversion of this pyrimidine precursor into nucleic acid pyrimidines was therefore limited. This amobarbital-orotate effect had properties of competitive inhibition.

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ACKNOWLEDGMENT This work was supported by USPHS Research Grant AI 04264 from the National Institute of Allergy and Infectious Diseases, N.I.H, Bethesda, Maryland.