Transport and Catabolism of d -Fructose by Spirillum itersonii

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Abstract
Spirillum itersonii ATCC 12639 utilized d -fructose but neither d -glucose nor d -gluconate as a sole source of carbon and energy. The substrate saturation kinetics for d -fructose and d -glucose uptake by whole cells indicated the presence of a carrier-mediated transport system for d -fructose but not for d -glucose. The d -fructose uptake activity was induced (10- to 12-fold increase) during growth on d -fructose-Casamino Acids (CA) or d -glucose-CA medium, but not CA alone. d -Fructose uptake activity was stimulated by Na + or Li + , but was inhibited by KCN, NaN 3 , 2,4-dinitrophenol, and p -chloromercuribenzoate. High specific activities of glucokinase, glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydratase, and 2-keto-3-deoxy-6-phosphogluconate aldolase were detected in extracts of cells cultured on d -fructose-CA medium. These enzymatic activities were undetectable in extracts of cells grown in CA or succinate-CA medium. No decrease in the maximally induced specific activities of these enzymes occurred after the addition of succinate to cells during exponential growth on d -fructose-CA. Fructose 1,6-diphosphate aldolase and glucose-6-phosphate isomerase specific activities were approximately the same irrespective of cultural conditions. These results indicated that d -glucose was not utilized by cells of S. itersonii because this bacterium was impermeable to this hexose.

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