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Chapter IV: The Lactose Permease System of Escherichia coli

Eugene P. Kennedy


The discovery of a specific system for the transport and accumulation of β-galactosides in Escherichia coli was reported in a preliminary account by Cohen and Rickenberg (1955). This was soon followed by a more complete description (Rickenberg et al., 1956) which made it clear that the transport system is an integral part of the mechanisms by which lactose is utilized in this organism. The 1956 paper also included a formal definition of the concept of permeases, introducing a terminology which was later to prove a source of controversy.

The independent studies of Pardee (1957) led to the finding in E. coli of a system for the accumulation of melibiose, an α-galactoside, and it was recognized that this system was identical with that described by Rickenberg et al. (1956). Later work led to the finding of a second transport system for melibiose, distinct from the lac system, (Prestidge and Pardee, 1965; Ganesan and Rotman, 1966).

In the original definition of permease this term was applied to the entire transport system (Rickenberg et al., 1956). A permease was defined as a system, protein in nature, resembling an enzyme in its properties of steric specificity and kinetics, that functions in the catalytic transfer of a substrate across the osmotic barrier of the cell. The authors explicitly stated that this definition did not make any assumptions about the mode of action of the permease, but did involve two essential hypotheses: first, that permease-catalyzed transport involves...

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