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Glucose Metabolism in 6-Phosphogluconolactonase Mutants of Escherichia coli

From the ¹ From the Department of Microbiology and Molecular Genetics, Harvard Medical School, Boston, Massachusetts 02115

Absence of 6-phosphogluconolactonase alone slightly decreases the growth rate of Escherichia coli on glucose. In such a strain there is considerable, and possibly normal, use of the oxidative hexose monophosphate shunt, according to ribose specific activity after growth on [1-¹⁴C]glucose. Thus, absence of lactonase, even in a strain with genetic deletion of lactonase, does not block the shunt.

A strain which lacks both phosphoglucose isomerase and glucose 6-phosphate dehydrogenase does not grow at all on glucose. A strain lacking isomerase and lactonase, however, does grow very slowly on glucose. Thus the shunt can function as the sole pathway of glucose metabolism in a lactonase mutant.

Metabolism of 6-phosphogluconolactone past the enzyme block of the mutant probably occurs mainly by spontaneous hydrolysis, giving the normal product, gluconate 6-phosphate. However, some metabolism uses a new sequence of reactions bypassing the lactonase: dephosphorylation and excretion of gluconolactone, hydrolysis of the gluconolactone in the medium, and uptake and phosphorylation of the gluconic acid.

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