Metabolism of 6-Mercaptopurine by Resistant Escherichia coli Cells

Coggin, Joseph H. (University of Chicago, Chicago, Ill.), Muriel Loosemore, and William R. Martin. Metabolism of 6-mercaptopurine by resistant Escherichia coli cells. J. Bacteriol. 92:446-454. 1966.-6-Mercaptopurine (MP) utilization as a source of purine in MP-sensitive and -resistant cultures of Escherichia coli was investigated. The label of MP-8-C(14) appeared in adenine and guanine of ribonucleic acid and deoxyribonucleic acid in sensitive and resistant cultures. Studies using MP-S(35) further demonstrated that the MP moiety was degraded, as shown by a rapid decrease in radioactivity from cells upon exposure to MP for 20 min. Enzymatic analysis showed that MP was converted to 6-mercaptopurine ribonucleotide (MPRP) by extracts derived from both sensitive and resistant cells. Resistant cell preparations, however, degraded MPRP to inosine monophosphate (IMP) rapidly when compared with analogue degradation by sensitive cells. Inosineguanosine-5'-phosphate pyrophosphorylase from resistant cells did not catalyze the synthesis of IMP from hypoxanthine when the cells were cultured in the presence of MP, but these enzyme preparations actively converted guanine to guanosine monophosphate (GMP). Pyrophosphorylase derived from resistant cells cultured in medium without MP catalyzed the conversion of hypoxanthine to IMP and also guanine to GMP. These observations suggest that inosine-guanosine-5'-phosphate pyrophosphorylase is composed of two distinct enzymes. The mode of resistance to MP in E. coli is related to an enhancement of the enzymatic degradation of MPRP to the pivotal purine intermediate, IMP.

The control of cell proliferation by preformed purines: a genetic study. I. Isolation and preliminary characterization of Chinese hamster lines with single or multiple defects in purine "salvage" pathways

Sublines with single or multiple defects in purine "salvage" enzymes were isolated from the Chinese hamster fibroblastic line GMA32 through single or successive one-step selections for resistance to purine analogs. They were examined for their ability to incorporate purine bases and nucleosides into macromolecules, for their sensitivity to growth inhibitory purines, and for their rescue by exogenous purines from deprivation imposed by metabolic inhibitors of endogenous synthesis. The results show that a deficiency of either adenosine kinase (EC 2.7.1.20), adenine phosphoribosyltransferase (EC 2.4.2.7) or hypoxanthine guanine phosphoribosyltransferase (EC 2.4.2.8) abolishes the ability of adenine to cause cell death by interfering with pyrimidine synthesis; on the other hand, the pyrimidine starvation caused by adenosine is fully prevented only by a deficiency of adenosine kinase.

Resistance to purine ribonucleoside analogues in an ascites tumor

A tumor subline (EAC-R2) which is resistant to the growth-inhibitory effects of 6-(methylmercapto)purine ribonucleoside (Me6MPR) and formycin has been selected from the Ehrlich ascites carcinoma (EAC) by repeated administration of Me6MPR during the propagation of the tumor. Some biochemical characteristics of the two tumor lines have been compared.Cells of the EAC-R2 tumor could not form phosphorylated derivatives of Me6MPR and formycin, whereas these metabolites were readily formed by EAC cells. Extracts of the resistant cells could not convert Me6MPR to the 5′-phosphate, indicating that they were deficient in purine ribonucleoside kinase activity.Me6MPR, formycin, and several other purine nucleoside analogues produced much less inhibition of purine synthesis de novo in EAC-R2 cells than in the parent line of cells. However, adenine produced a similar degree of inhibition in both tumor lines, indicating that this pathway in the resistant variant is susceptible to feedback inhibition.It is proposed that a deficiency of purine ribonucleoside kinase(s) may be responsible for the inability of Me6MPR and formycin to inhibit the growth of the EAC-R2 tumor.