This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Bresnick, E. Articles by Hitchings, G. H. Search for Related Content PubMed Articles by Bresnick, E. Articles by Hitchings, G. H.

Feedback Control in Ehrlich Ascites Cells^*

( Burroughs Wellcome and Co. [U.SA.], Inc., Wellcome Research Laboratories, Tuckahos, New York)

Both carbamyl phosphate-aspartate transcarbamylase and dihydroorotase were found to be present in cell-free preparations from Ehrlich ascites tumor. Both enzymes were inhibited by various pyrimidines and derivatives thereof. Uridine-5'-phosphate was the most potent inhibitor of carbamyl phosphate-aspartate transcarbamylase, whereas fluoroorotic acid, orotic acid, and orotidine were most effective against dihydroorotase. These data demonstrate feedback control by preformed pyrimidine derivatives upon at least two of the steps which are involved in the biosynthesis of pyrimidines. Since pyrimidine analogs exhibit similar inhibitory effects, the results support the view that these antimetabolites may inhibit the biosynthesis of pyrimidines, in addition to their competitions with the products.

^* Presented in part at the 51st Annual Meeting of the American Association for Cancer Research, April 8–10, 1960, Chicago, Ill.

Received 8/31/60.