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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 m values for substrates and cofactor NADP+. The two dehydrogenases were relatively unstable in extracts prepared from early stages of development. The K m 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 intermediates 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.
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