U does not degrade D-glucose through the glycolytic pathway but requires (i) its oxidation to -gluconic acid by a peripherally located constitutive glucose dehydrogenase (insensitive to osmotic shock), (ii) accumulation of -gluconic acid in the extracellular medium, and (iii) the induction of a specific energy-dependent transport system responsible for the uptake of -gluconic acid. This uptake system showed maximal rates of transport at 30 ° in 50 mM potassium phosphate buffer, pH 7.0. Under these conditions the Km calculated for -gluconic acid was 6.7 μM. Furthermore, a different transport system, specific for the uptake of glucose, was also identified. It is active and shows maximal uptake rates at 35 ° in 50 mM potassium phosphate buffer, pH 6.0, with a value of 8.3 μM.


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