Factors affecting the interconversion of ornithine decarboxylase forms in Physarum polycephalum
Kottas, G. Elizabeth
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The conversion between the two forms of ornithine decarboxylase (ODC) has been shown to occur rapidly and reversibly in Physarum polycephalum with slight changes in the osmolality of the organism's growth media. The ratio of the two forms changes while total enzyme activity remains constant over time. This effect was shown to be more pronounced with the presence of the ionophores, gramicidin S and valinomycin. However, the addition of 1 mM ouabain caused no variation in ODC activity. Experiments with metabolic inhibitors such as lowered temperatures, sodium azide and 2,4 dinitrophenol support the idea that the maintenance of the equilibrium between the two forms of ODC is correlated with the generation of metabolic energy. It was shown that the presence of these inhibitors always inhibited conversion to the active form of the enzyme. Whereas conversion to the less active-enzyme form was affected little, if at all, under the same experimental conditions. Inhibitors of metabolic energy such as 0.02% sodium azide and 2 mM 2,4 dinitrophenol also induced a substantial loss in total ornithine decarboxylase activity. Such a decrease in total activity has not been previously shown in this organism.