Amino acid pool and protein turnover during differentiation (spherulation) ofPhysarum polycephalum |
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Authors: | Gertrud Wendelberger-Schieweg Aloys Hüttermann |
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Affiliation: | (1) Unité de Microscopie Electronique, Département de Biologie Moléculaire, Institut Pasteur, 25 rue du Docteur Roux, F-75724 Paris Cédex 15, France;(2) Present address: Department of Medical Bacteriology, University of Alberta, Medical Sciences Building, T6G 2H7 Edmonton, Alberta, Canada |
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Abstract: | The composition of the amino acid pool during spherulation was determined. It changes in size and in composition, the concentration of each amino acid behaving individually. The first response to the onset of spherulation either by starvation or osmotic shock (0.5 M mannitol) always is a decrease of the pool's size, which during further starvation expands for a short period and then decreases again. During development induces by mannitol in the presence of external amino acids, the pool size increases continuously after the initial depletion.As shown by radioactive labeling, amino acids were actively released from the plasmodium into a medium containing amino acids, but retained by the microplasmodia in an amino acid-free medium. The kinetics of the uptake of radioactive amino acids from the medium is biphasic, indicating the existence of multiple pools. Even after a labeling period of 8 h the amino acid pool is not yet in equilibrium with the medium. The possibility of a compartimentation of the pool was confirmed by density labeling of two different enzymes.Whereas the turnover of total protein is only very low during growth, it is rather high in spherulating microplasmodia. At least 70% of the originally existing protein is degraded during this development, while, simultaneously, at least 50% of the protein present after 24 h starvation is newly synthesized during that period. |
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Keywords: | Bacillus subtilis Sporulation Uracil incorporation Autoradiography Nuclear shape |
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