Dissociation of a galactose transport system by warm-water treatment

Abstract

When E. coli A is warmed for several minutes at 48°, while suspended in 0.1 M Tris buffer (pH 7.3) containing 10 mM MgCl 2, its viability is retained undiminished and its growth is initiated without lag. Little macromolecular substance is released from the cells into the medium, although an appreciable release of soluble nucleotide derivatives and peptidic materials does occur. Galactose uptake, which is usually biphasic, is dissociated by warm-water treatment. The extremely rapid, respiration-independent primary phase is retained, while the slow, respiration-dependent secondary phase is reduced. The secondary phase can be restored by incubating the treated cells in the chloramphenicol-containing uptake medium in air, but not in an atmosphere of N 2. As a result of warm-water treatment, the cells may become depleted locally of ATP or its metabolic equivalent, which is needed to activate and sustain the uptake system. However, this interpretation could not be verified by supplementing the treated cells with ATP, MgCl 2 or the warm-water extract. Further analysis revealed that the cells contain a constant amount of phosphorylated galactose during transport and that it is free galactose which accumulates. Since it occurs during the secondary phase of uptake, dephosphorylation of the transport intermediate may be coupled to respiration, and it may be this process which is sensitive to warm-water treatment.