Proline uptake by disrupted membrane preparations from Escherichia coli

Abstract

Isolated membrane preparations from E. coli W6, a proline auxotroph, continue to catalyze energy-dependent proline uptake after disruption by sonication or passage through a French pressure cell. Membranes from E. coli W157, a mutant deficient in proline uptake and exchange capacity, do not catalyze proline uptake before or after disruption. The proline uptake by the sonicated W6 preparations is not due to undisrupted membranes and the proline taken up is loosely associated with a particulate, sedimentable fraction. This uptake system is inhibited by the same metabolic inhibitors that inhibit proline uptake by intact membranes, has the same temperature optimum as intact membranes, and displays similar responses to osmolarity changes as intact membranes. Furthermore, in electron micrographs, sonicated membranes appear to be identical to intact membranes. With the exception of size, both preparations consist of grossly intact vesicles. Finally, it is demonstrated by light scattering techniques that sonicated membrane vesicles respond to changes in the concentrations of either sucrose or potassium phosphate in the same manner as undisrupted membranes.