Compartmentation of the Metabolism of Lactose, Galactose and Glucose in Escherichia coli

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Abstract
Compartmentation phenomena were studied in the course of the simultaneous metabolism of glucose, galactose and lactose by organisms of E. coli induced for either the lac operon, the gal operon, both or neither. Metabolic patterns were investigated in each phenotype by incubating parallel identical cultures with the 3 sugars in equal chemical concentration but labelled differently with 14C. The 4 labelled substrates were glucose, galactose and lactose labelled exclusively in the glucose moiety or the galactose moiety. The metabolites from free glucose in the medium equilibrated with those from free galactose in the medium but did not equilibrate with metabolic products from glucose generated endogenously by the hydrolysis of lactose. Metabolic products from galactose formed in the hydrolysis of lactose equilibrated with those from glucose from the same source, but not with metabolic intermediates formed from either free glucose or free galactose in the medium. Other interpretations of these results, not involving metabolic compartmentation, were found inadequate to account for the results. Some of the implications of compartmentation in bacteria are discussed.

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