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: 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.Journal of general microbiology 08/1979; 113(2):357-368. DOI:10.1099/00221287-113-2-357
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ABSTRACT: The cellular slime mould Dictyostelium mucoroides exhibits clear dimorphism in development which, depending upon environmental conditions, leads to (1) macrocyst formation, a sexual process or (2) sorocarp formation, an asexual process. The present work was undertaken to determine the role of protons in the determination of the developmental mode. Intracellular pH (pHi) was measured at the single-cell level microfluorometrically by use of the pH-sensitive fluorescent dye carboxfluorescein. The proton-pump inhibitor diethylstilboestrol, the protonophore 2,4-dinitrophenol and a weak acid, propionate, were found to convert the developmental mode from macrocyst to sorocarp formation under conditions otherwise favouring macrocyst formation. All of these drugs lowered pHi. Although no significant difference in pHi was detected between dissociated cells shaken in buffers of pH 5.0 and pH 7.0, a marked difference in pHi arose between the two if 5 mM-NH,Cl was included to simulate the expected microenvironment in the cell mass during development. Comparison of the pHi of cells developing toward sorocarps with that of cells developing toward macrocysts revealed a few cells with extremely high pHi (> 7.30) in the latter population. The results obtained suggested that pHi, or something related to pHi, influences the development a1 choice.Journal of general microbiology 09/1990; 136(9). DOI:10.1099/00221287-136-9-1739
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ABSTRACT: Esterase activity was induced in Aspergillus niger only during conidiation and not in sterile cultures, irrespective of the source of nitrogen for growth. The increase in esterase activity during conidiation was observed cytochemically to occur in the conidiophore tip prior to the formation of the vesicle and phialides and in the latter structures after their formation. Electrophoresis of cell-free extracts of conidiating mycelia revealed a multimolecular esterase profile; with one exception (this only contained one band and was therefore unimolecular) no esterase profile was obtained from sterile cultures although such extracts contained a low basal esterase activity. In this study a causal relationship between a biochemical event and a morphological character in a fungus has been firmly established.Transactions of the British Mycological Society 08/1972; 59(1). DOI:10.1016/S0007-1536(72)80041-X