Compartmentation of the metabolism of lactose, galactose and glucose in Escherichia coli.

Abstract

SUMMARY: Compartmentation phenomena were studied in the course of the simultaneous metabolism of glucose, galactose and lactose by organisms of Escherichia coli which were 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 three sugars in equal chemical concentration but labelled differently with 14C. The four labelled substrates were glucose, galactose and lactose labelled either exclusively in the glucose moiety or exclusively in 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 derived from glucose generated endogenously by the hydrolysis of lactose. Similarly, metabolic products derived 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, have been considered and found inadequate to account for the observed results. Some of the implications of compartmentation in bacteria are discussed.