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5-Fluoropyrimidine-resistant mutants of pneumococcus
Abstract:
Three classes of 5-fluorpyrimidine-resistant mutants of Diplococcus pneumoniae have been characterized. The mutant strain upp is resistant to high concentrations of the fluoropyrimidine bases fluorouracil (FU) and fluorocytosine (FC); strain upp has a defective uridine monophosphate pyrophosphorylase. The mutant strain udk is resistant to inhibition by fluorouridine (FUR) and exhibits defective uridine kinase activity. The mutant strain fun is resistant to inhibition by the nucleosides fluorodeoxyuridine, fluorodeoxycytidine, and FUR, but shows normal activity for all pyrimidine pathway enzymes tested. This strain may be defective in the activity of a transport system that governs the cellular uptake of pyrimidine ribo- and deoxyribonucleosides. Biochemical studies on wild-type and fluoropyrimidine-resistant pneumococci are discussed with respect to the transport and early metabolism of preformed pyrimidine precursors by this organism.
Insights
Researchers identified three Diplococcus pneumoniae mutants resistant to 5-fluoropyrimidines. These mutants reveal insights into pyrimidine metabolism and transport, specifically the roles of uridine monophosphate pyrophosphorylase and uridine kinase.
Area of Science:
- Microbiology
- Biochemistry
- Molecular Biology
Background:
- 5-Fluoropyrimidines are critical antimicrobial and anticancer agents.
- Understanding resistance mechanisms in bacteria like Diplococcus pneumoniae is essential for drug efficacy.
- Pyrimidine metabolism and nucleoside transport are key cellular processes.
Purpose of the Study:
- To characterize 5-fluoropyrimidine-resistant mutants of Diplococcus pneumoniae.
- To elucidate the biochemical basis of resistance.
- To investigate the roles of specific enzymes and transport systems in pyrimidine precursor utilization.
Main Methods:
- Isolation and characterization of three distinct 5-fluoropyrimidine-resistant mutant strains (upp, udk, fun).
- Enzyme activity assays for pyrimidine pathway enzymes, including uridine monophosphate pyrophosphorylase and uridine kinase.
- Comparative biochemical studies on wild-type and mutant strains.
Main Results:
- Mutant upp showed resistance to fluorouracil and fluorocytosine, linked to defective uridine monophosphate pyrophosphorylase.
- Mutant udk exhibited resistance to fluorouridine, associated with deficient uridine kinase activity.
- Mutant fun was resistant to multiple fluoropyrimidine nucleosides but possessed normal enzyme activities, suggesting a defect in nucleoside transport.
Conclusions:
- The study identified specific enzymatic defects (upp and udk) and a potential transport system defect (fun) underlying 5-fluoropyrimidine resistance in D. pneumoniae.
- These findings highlight the importance of pyrimidine salvage pathways and nucleoside uptake in mediating drug sensitivity.
- The characterized mutants serve as valuable tools for further research into pyrimidine metabolism and transport in bacteria.