TY - JOUR T1 - THE EFFECT OF 6-MERCAPTOPURINE ON NUCLEIC ACID BIOSYNTHESIS IN <em>ESCHERICHIA COLI</em> JF - Journal of Pharmacology and Experimental Therapeutics JO - J Pharmacol Exp Ther SP - 195 LP - 202 VL - 120 IS - 2 AU - H. George Mandel AU - Joseph K. Inscoe AU - Harriet M. Maling AU - Paul K. Smith Y1 - 1957/06/01 UR - http://jpet.aspetjournals.org/content/120/2/195.abstract N2 - 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 &amp; Wilkins Co. ER -