Metabolism of major cell components during slime mold morphogenesis.
ABSTRACT Morphogenetically synchronized Dictyostelium discoideum amoeba were sampled at intervals during development to determine the fates of major cell constituents. Dry weight, total protein and fractions thereof, RNA, free and bound hexoses were followed. None of these except the last appeared to reflect the specific morphogenetic events. Two polysaccharide fractions were encountered which did reflect these events and their syntheses were repressed or disturbed in morphogenetically deficient mutants.
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ABSTRACT: The social amoeba Dictyostelium discoideum represents an attractive host organism for the production of heterologous proteins. However, its application is seriously affected by slow growth rates as well as low maximal cell densities in the presence of axenic (liquid) media. Starting with standard complex media the influence of certain medium components was investigated. The kind and concentration of carbohydrates, the concentration of salt and ammonia and the supplementation of conditioned media were varied. These studies were performed by following cell growth in batch experiments over the whole growth cycle into the decline phase to obtain information about growth rates as well as maximal cell densities. Only maltose, glucose and α-trehalose were metabolised at significant rates. The concentration of ammonia produced correlated inversely with the concentration of carbohydrates metabolised. Under standard conditions ammonia reached concentrations of about 50 mM, most being produced during stationary phase. Ionic strength and the addition of ammonia affected the growth rate as well as the maximal cell density. Ammonia did not limit maximal cell density. D. discoideum can be cultivated in normal stirred bioreactors. A semi-empirical model is discussed for the description of the growth behaviour.Process Biochemistry 01/2003; 39(3):333-343. · 2.44 Impact Factor
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ABSTRACT: Cell-free extracts of Dictyostelium discoideum contained the enzymes necessary for both oxidative and non-oxidative pentose phosphate metabolism. The specific activities of these enzymes changed little during differentiation. The properties of glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase were studied with respect to K, values for substrates and cofactor NADPf. The two dehydrogenases were relatively unstable in extracts prepared from early stages of development. The K, value of phospho- glucose isomerase for glucose 6-phosphate was approximately 30-fold higher than that of glucose-6-phosphate dehydrogenase. Measurements of pentose phosphate pathway inter- mediates were made throughout development. All measured intermediates except fructose 1,6-bisphosphate appeared to accumulate between aggregation and culmination. Fructose 1,6-bisphosphate concentrations remained constant until culmination, then dropped 3-fold during sorocarp construction. Calculation of mass-action ratios for the pentose phosphate reactions suggested that glucose-6-phosphate dehydrogenase was the only reaction greatly displaced from equilibrium. These results are discussed in relation to factors controlling pentose phosphate metabolism during development in D. discoideum.Microbiology-sgm. 01/1979; 113(2):357-368.