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Is beta-poly(L-malate) synthesis catalysed by a combination of beta-L-malyl-AMP-ligase and beta-poly(L-malate)
B Willibald1, W Bildl, B S Lee
1Institut für Biophysik und Physikalische Biochemie der Universität, Regensburg, Germany.
Abstract:
beta-Poly(L-malate) is supposed to function in the storage and transport of histones, DNA polymerases and other nuclear proteins in the giant syncytical cells (plasmodia) of myxomycetes. Here we report on the biosynthesis of [14C]beta-poly(L-malate) from injected L-[14C]malate in the plasmodium of Physarum polycephalum. The effects of KCN, arsenate, adenosine 5'-(alpha, beta-methylene)triphosphate, adenosine 5'-(beta, gamma-methylene)triphosphate, guanosine 5'-(beta, gamma-methylene)triphosphate, desulfo coenzyme A and phenylarsinoxid on beta-poly(L-malate) synthesis were studied after their coinjection with L-[14C]malate. The synthesis was not affected by KCN or desulfo coenzyme A, but was blocked by arsenate and adenosine 5'-(alpha,beta-methylene)triphosphate. The plasmodium lysate catalysed an L-malate-dependent ATP-[32P]pyrophosphate exchange, but was devoid of beta-poly(L-malate) synthetic activity under all experimental conditions tested. The results suggested an extramitochondrial synthesis of beta-poly(L-malate), involving the polymerization of beta-L-malyl-AMP. It is assumed that the lack of synthesis in the lysate is caused by the inactivation of beta-poly(L-malate) polymerase involving a cell injury kinase pathway. Because injected guanosine 5'-(beta, gamma-methylene)triphosphate blocks the synthesis, the injury signal is likely to be GTP dependent.
Insights
Beta-poly(L-malate) synthesis in Physarum polycephalum occurs outside mitochondria, likely involving beta-L-malyl-AMP polymerization. Cell injury may inactivate the polymerase via a GTP-dependent pathway.
Area of Science:
- Biochemistry
- Cell Biology
- Mycology
Background:
- Beta-poly(L-malate) is implicated in nuclear protein transport in myxomycete plasmodia.
- Its precise synthesis pathway and regulation remain largely uncharacterized.
Purpose of the Study:
- To investigate the biosynthesis of beta-poly(L-malate) in Physarum polycephalum.
- To identify factors affecting beta-poly(L-malate) synthesis and elucidate its cellular location.
Main Methods:
- In vivo biosynthesis studies using radiolabeled L-malate.
- Inhibition studies with various chemical agents and nucleotide analogs.
- Analysis of plasmodium lysate for enzymatic activity.
Main Results:
- Beta-poly(L-malate) synthesis was observed from L-[14C]malate.
- Synthesis was inhibited by arsenate and adenosine 5'-(alpha, beta-methylene)triphosphate.
- Plasmodium lysate showed L-malate-dependent ATP-pyrophosphate exchange but lacked polymerization activity.
Conclusions:
- Extramitochondrial synthesis of beta-poly(L-malate) is suggested, potentially via beta-L-malyl-AMP polymerization.
- Cell injury may trigger a GTP-dependent kinase pathway, inactivating beta-poly(L-malate) polymerase.