Purified reconstituted lac carrier protein from Escherichia coli is fully functional.

Publisher Website
Google Scholar
Abstract
Proteoliposomes reconstituted with lac carrier protein purified from the plasma membrane of E. coli catalyze each of the translocation reactions typical of the .beta.-galactoside transport system (i.e., active transport, counterflow, facilitated influx and efflux) with turnover numbers and apparent Km values comparable to those observed in right-side-out membrane vesicles. Detailed kinetic studies show that the reconstituted system exhibits properties analogous to those observed in membrane vesicles. Imposition of a membrane potential (.DELTA..PSI., interior negative) causes a marked decrease in apparent Km (by a factor of 7-10) with a smaller increase in Vmax (.apprxeq. 3-fold). At submaximal values of .DELTA..PSI., the reconstituted carrier exhibits biphasic kinetics, with 1 component manifesting the kinetic parameters of active transport and the other exhibiting the characteristics of facilitated diffusion. At low lactose concentrations, the initial velocity of influx varies linearly with the square of the proton electrochemical gradient. The results provide quantitative support for the contention that a single polypeptide species, the product of the lacY gene, is responsible for each of the transport reactions typical of the .beta.-galactoside transport system.

This publication has 35 references indexed in Scilit: