RT Journal Article SR Electronic T1 THE EFFECT OF 6-MERCAPTOPURINE ON NUCLEIC ACID BIOSYNTHESIS IN ESCHERICHIA COLI JF Journal of Pharmacology and Experimental Therapeutics JO J Pharmacol Exp Ther FD American Society for Pharmacology and Experimental Therapeutics SP 195 OP 202 VO 120 IS 2 A1 H. George Mandel A1 Joseph K. Inscoe A1 Harriet M. Maling A1 Paul K. Smith YR 1957 UL http://jpet.aspetjournals.org/content/120/2/195.abstract AB The growth of Escherichia coli was inhibited partially by the carcinostatic purine analog, 6-mercaptopurine (6-MP), at a concentration of 3 mgm. per liter in a glucose-salts medium, without change in viability or gross morphology of the microorganisms. Simultaneous addition of 5 mgm. of guanine per liter of medium partially reversed this inhibition without the added guanine becoming the sole source of bacterial purines. DNA and RNA purines were isolated from bacteria grown with 5 mgm. of guanine-C14 in the presence and absence of 3 mgm. of 6-MP per liter. The relative specific activities (RSA's) of both RNA and DNA adenine obtained from cultures grown in the presence of 6-MP were approximately 60 per cent higher than those of control cultures, whereas the corresponding guanine fractions showed only a slight increase. Utilization of exogenous guanine for the same extent of growth was unaffected by 6-MP. The increase in the RSA's of bacterial purines was due to a lessened dilution of the labeled exogenous purine by endogenous purine since experiments with labeled formate demonstrated a reduction in endogenous purine synthesis produced by 6-MP. Although this curtailment was approximately equal for adenine and guanine, 6-MP affected the RSA's of the nucleic acid adenine fractions more than those of the guanine fractions because a larger proportion of adenine than guanine is endogenously synthesized when guanine-C14 is added to the growth medium. © 1957 by The Williams & Wilkins Co.