Related Experiment Videos
The uptake and metabolism of uridine by the slime mould Physarum polycephalum
Abstract:
1. Uridine is taken up by microplasmodia of Physarum polycephalum via a saturatable transport system with an apparent Km of 29 muM. An intracellular concentration significantly higher than that in the growth medium is attained, suggesting that the uptake is an active process. Both deoxyribonucleosides and ribonucleosides are competitive inhibitors of the uptake of uridine. 2. In contrast, the rate of entry of uridine into surface plasmodia is a linear function of the concentration of the nucleoside in the growth medium, and the uptake is not inhibited by other nucleosides. 3. As well as serving as a source of pyrimidine nucleotides for the synthesis of nucleic acids, uridine is also catabolised by P. polycephalum. Uracil accumulates in the growth medium and there is also significant conversion of C-2 of the pyrimidine ring to CO2. The proportion of uridine subject to catabolism in surface plasmodia is less than that observed for microplasmodia.
Insights
Physarum polycephalum actively transports uridine into microplasmodia via a saturable system. Surface plasmodia exhibit linear uridine uptake, with both stages catabolizing uridine differently.
Area of Science:
- Cell Biology
- Biochemistry
- Mycology
Background:
- Uridine is a vital nucleoside for nucleic acid synthesis.
- Understanding nucleoside transport and metabolism is crucial for cell physiology.
- Physarum polycephalum serves as a model organism for studying cellular processes.
Purpose of the Study:
- To investigate the uptake mechanisms of uridine in different life stages of Physarum polycephalum.
- To characterize the kinetics and regulation of uridine transport.
- To determine the metabolic fate of uridine within the organism.
Main Methods:
- Uptake assays using radiolabeled uridine.
- Kinetic analysis to determine Km and Vmax values.
- Competitive inhibition studies with various nucleosides.
- Analysis of catabolic products (uracil, CO2) in the growth medium.
Main Results:
- Microplasmodia display saturable, active uridine uptake (Km = 29 μM), inhibited by other nucleosides.
- Surface plasmodia show linear, non-inhibited uridine uptake.
- Both life stages catabolize uridine, with uracil accumulation and CO2 production observed.
- Microplasmodia exhibit a higher proportion of uridine catabolism compared to surface plasmodia.
Conclusions:
- Physarum polycephalum employs distinct uridine transport systems in its microplasmodial and surface plasmodial stages.
- Uridine serves dual roles as a precursor for nucleotide synthesis and a substrate for catabolism.
- Differential catabolism rates suggest stage-specific metabolic regulation in Physarum polycephalum.