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Acid-soluble purine and pyrimidine derivatives of growing, encysting and encystment-inhibited amoebae
1Department of Biology, University of Houston, TX 77204-5513.
Abstract:
The intracellular acid-soluble purine and pyrimidine derivatives of myxamoebae-swarm cells of Physarum flavicomum were investigated during growth, microcyst formation, and during adenine-inhibition of encystment, using high performance liquid chromatography (HPLC). We also studied the incorporation of exogenous radioactive adenine into the acid soluble purine derivatives and S-adenosyl-sulphur compounds separated by HPLC. The most abundant ribonucleoside monophosphate was AMP in the growing and 15 h encysting cells (NC), while it was UMP in the 15 h adenine-inhibited cells (AIC). ADP was the nucleoside diphosphate present in the greatest quantity in the growing and NC cells but it was CDP in the AIC. The nucleoside triphosphate in highest concentration was ATP, UTP, and GTP in growing, NC, and AIC, respectively. Guanosine was the most abundant nucleoside in all cells. The nucleobase occurring in greatest concentration was cytosine, cytosine and guanine, and adenine in the growing, NC, and AIC, respectively. The AMP content in the 15 h AIC was 2.1-fold higher than that of adenosine. The 15 h NC had the lowest adenylate energy charge, a value of 0.54 +/- 0.02, while the values for growing cells and the AIC were 0.62 +/- 0.02 and 0.76 +/- 0.01, respectively. [14C]-Adenine labelling studies (15 h) revealed the occurrence of purine nucleotide interconversion, as the label was detected not only in adenosine, AMP, ADP, ATP, but also in guanine, guanosine, GMP, GDP, GTP, as well as, in inosine monophosphate and xanthosine monophosphate. The percentage incorporation of the radiolabelled adenine into AMP was higher than into adenosine. An increased intracellular level of guanine nucleotides is associated with the inhibition of encystment. The extracellular adenine, rather than internal adenine sources, appears to be the primary precursor of nucleotide for S-adenosylmethionine synthesis during adenine-inhibition of encystment.
Insights
Adenine affects Physarum flavicomum encystment by altering nucleotide levels. Extracellular adenine is key for S-adenosylmethionine synthesis during inhibited encystment, impacting guanine nucleotide levels.
Area of Science:
- Biochemistry
- Cell Biology
- Mycology
Background:
- Physarum flavicomum undergoes microcyst formation, a process sensitive to environmental cues.
- Nucleotide metabolism plays a crucial role in cellular differentiation and development.
Purpose of the Study:
- To investigate intracellular purine and pyrimidine derivatives during growth, microcyst formation, and adenine-inhibited encystment in Physarum flavicomum.
- To examine the incorporation of exogenous radioactive adenine into nucleotide compounds.
Main Methods:
- High-performance liquid chromatography (HPLC) was used to analyze acid-soluble purine and pyrimidine derivatives.
- Radioactive [14C]-adenine labeling was employed to trace nucleotide interconversion and synthesis pathways.
Main Results:
- Adenine-inhibited encysting cells showed distinct nucleotide profiles, with higher UMP, CDP, and GTP compared to growing and normal encysting cells.
- Adenylate energy charge was lowest in normally encysting cells and highest in adenine-inhibited cells.
- Radioactive adenine incorporated into various purine derivatives, indicating interconversion, with higher incorporation into AMP than adenosine.
- Increased intracellular guanine nucleotides correlated with encystment inhibition.
Conclusions:
- Adenine significantly alters the intracellular nucleotide composition of Physarum flavicomum during encystment.
- Extracellular adenine is preferentially utilized for S-adenosylmethionine synthesis during adenine-induced encystment inhibition.
- Changes in guanine nucleotide levels are linked to the inhibition of the encystment process.