Two distinct types of trimethoprim-resistant dihydrofolate reductase specified by R-plasmids of different compatibility groups.
R-Plasmids from a number of trimethoprim-resistant Escherichia coli and Citrobacter sp. were studied after transfer to E. coli K12 hosts. Each was found to specify a dihydrofolate reductase which was resistant to trimethoprim and Methotrexate, and which could be completely separated from the host chromosomal enzyme by gel filtration. Two distinct types of R-plasmid dihydrofolate reductases were identified. Type I enzymes, typified by the R483 enzyme previously described (Sköld, O., and Widh, A. (1974) J. Biol. Chem. 249, 4324-4325), are synthesized in amounts severalfold higher than the chromosomal enzyme. The 50% inhibitory concentrations (I50) of trimethoprim, Methotrexate, and aminopterin are increased several thousandfold over the corresponding values for the chromosomal enzyme. Type II R-plasmid dihydrofolate reductases are synthesized in about the same amount, or less, as the chromosomal enzyme, but are practically several hundredfold higher than those for the type I enzymes. Both types of R-plasmid dihydrofolate reductase showed little difference from the chromosomal enzyme in the binding of dihydrofolate, NADPH, folic acid, and 2,4-diaminopyrimidine.
D002876:Chromosomes, Bacterial / Q000201:enzymology; D004352:Drug Resistance, Microbial; D004926:Escherichia coli / Q000187:drug effects / Q000201:enzymology*; D005111:Extrachromosomal Inheritance / Q000187:drug effects*; D006863:Hydrogen-Ion Concentration; D007527:Isoenzymes / Q000096:biosynthesis*; D007700:Kinetics; D008727:Methotrexate / Q000494:pharmacology; D009249:NADP; D010641:Phenotype; D010957:Plasmids / Q000187:drug effects*; D014176:Protein Biosynthesis / Q000187:drug effects*; D013045:Species Specificity; D013762:Tetrahydrofolate Dehydrogenase / Q000096:biosynthesis*; D014158:Transcription, Genetic / Q000187:drug effects*; D014295:Trimethoprim / Q000494:pharmacology*
D007527:Isoenzymes; D009249:NADP; D014295:Trimethoprim; D013762:Tetrahydrofolate Dehydrogenase; D008727:Methotrexate