title: Nuclear accumulation and homeostasis of the unusual polymer beta-poly (L-malate) in plasmodia of Physarum polycephalum.
abstract: The plasmodium of Physarum polycephalum specifically contains an unusual polyester, beta-poly(L-malate), which is not found in any of the mononucleate forms of its life cycle. Plasmodia growing on D-glucose have been analyzed for beta-poly(L-malate) in nuclei, cytosol and culture medium after cell fractionation, purification by chromatography on DEAE-cellulose and digestion of proteins/nucleic acids. Nuclei contained 400 micrograms polymer per 1 g of plasmodia, corresponding to a nuclear concentration of 230 mM L-malyl residues, not depending on growth rates, lengths of growth periods, and the growth form as micro- or macroplasmodia. The synthetic rate increased during the phase of rapid enlargement of the nuclei after mitosis. Beta-Poly(L-malate) was polydisperse in molecular mass, these tending to be higher in nuclear than in cytosolic extracts and being lowest in the culture medium. Beta-Poly(L-malate) was not degraded when contained in plasmodia, in contrast to degradation and the occurrence of low molecular mass polymer in the culture medium. During pulse-chase feeding with D-[14C]glucose (0.8 micrometerCi/mol), beta-[14C]poly(L-malate) appearance followed kinetics indicating a release of polymer from nuclei into the culture medium when it was in excess of a threshold. Injection experiments with purified beta-[14C]poly(L-malate) revealed a re-entry from the cytoplasm into the nuclei and thus the possibility of commutation between the cytoplasm and the nuclei. The observed homeostasis in nuclei supports the assumption that beta-poly(L-malate) plays an essential role in growing plasmodia.
authors.affiliation: Institut für Biophysik und physikalische Biochemie, Universität Regensburg, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Schmidt
authors.forename: C
authors.initials: C
authors.lastname: Windisch
authors.forename: E
authors.initials: E
authors.lastname: Holler
mesh_terms: D000818:Animals; D002458:Cell Fractionation; D002467:Cell Nucleus / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000378:metabolism*; D005947:Glucose / Q000494:pharmacology; D008293:Malates / Q000378:metabolism*; D016839:Physarum polycephalum / Q000378:metabolism*; D010961:Plasmodium / Q000187:drug effects / Q000378:metabolism*; D011108:Polymers / Q000378:metabolism*; D013997:Time Factors
chemical_list: D004791:Enzyme Inhibitors; D008293:Malates; D011108:Polymers; C074640:poly(malate); D005947:Glucose