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Pyrimidine metabolism in microplasmodia of Physarum polycephalum
Abstract:
If microplasmodia of Physarum polycephalum are exposed to 14C-labelled pyrimidine nucleosides or bases, an unusual pattern of metabolism is found. Only the nucleosides are taken up. Analysis of the distribution of the radioactivity in the cells revealed that ribonucleosides and deoxyribonucleosides are incorporated into nucleotides; however, a substantial catabolism takes place. Thus incubation with [2-14C]pyrimidine nucleosides readily gives rise to [14C]O2, particularly in the case of [2-14C]thymidine. Due to this a significant part of the trichloroacetic-acid-insoluble radioactivity from exogenously supplied [2-14C]thymidine is not associated with DNA. The pattern of labelling of nucleoside triphosphates from exogenously supplied nucleosides indicated that the de novo synthesis of nucleotides was only partly repressed. An unusual conversion of deoxycytidine into cytidine was noted. Enzyme analysis on cell-free extracts revealed that pyrimidine nucleosides can be salvaged by kinases and that their initial catabolism is initiated by hydrolases. Incubation of microplasmodia with pyrimidine analogues showed that only nucleoside analogues are toxic. The experimental results have led us to propose a scheme for the metabolism of pyrimidine nucleosides and bases in Physarum polycephalum.
Insights
Physarum polycephalum incorporates pyrimidine nucleosides into nucleotides but also extensively catabolizes them, releasing carbon dioxide. This metabolism affects DNA labeling and reveals unique salvage and conversion pathways for pyrimidines.
Area of Science:
- Biochemistry
- Cell Biology
- Mycology
Background:
- Pyrimidine metabolism is crucial for cellular function.
- Understanding nucleotide salvage and catabolism pathways is essential for comprehending cellular energetics and biosynthesis.
- Physarum polycephalum offers a unique model system for studying fundamental cellular processes.
Purpose of the Study:
- To investigate the metabolic fate of pyrimidine nucleosides and bases in Physarum polycephalum.
- To elucidate the pathways of pyrimidine salvage, incorporation, and catabolism.
- To determine the toxicity of pyrimidine analogues in this organism.
Main Methods:
- Incubation of Physarum polycephalum microplasmodia with 14C-labelled pyrimidine nucleosides and bases.
- Analysis of radioactivity distribution within cellular fractions.
- Enzyme assays on cell-free extracts.
- Incubation with pyrimidine analogues to assess toxicity.
Main Results:
- Only pyrimidine nucleosides, not bases, were taken up by microplasmodia.
- Ribonucleosides and deoxyribonucleosides were incorporated into nucleotides, with significant catabolism observed.
- [14C]O2 was readily produced from [2-14C]pyrimidine nucleosides, especially [2-14C]thymidine.
- Exogenous [2-14C]thymidine incorporation into DNA was limited due to catabolism.
- De novo nucleotide synthesis was only partially repressed.
- An unusual conversion of deoxycytidine to cytidine was detected.
- Pyrimidine nucleosides are salvaged by kinases and catabolized by hydrolases.
- Only pyrimidine nucleoside analogues exhibited toxicity.
Conclusions:
- Physarum polycephalum exhibits a distinct pyrimidine nucleoside metabolism characterized by significant catabolism.
- The organism possesses active salvage pathways for pyrimidine nucleosides.
- The study proposes a comprehensive scheme for pyrimidine nucleoside and base metabolism in Physarum polycephalum.
- Pyrimidine nucleoside analogues represent potential targets for antimicrobial strategies.