TRANSPORT OF SUGARS AND AMINO-ACIDS IN BACTERIA .18. PROPERTIES OF AN ISOLEUCINE CARRIER IN CYTOPLASMIC MEMBRANE-VESICLES OF ESCHERICHIA-COLI

  • 1 January 1977
    • journal article
    • research article
    • Vol. 81  (5) , 1517-1523
Abstract
The properties of the carrier for isoleucine in E. coli were studied using cytoplasmic membrane vesicles (IM vesicles). The IM vesicles exhibited respiration-dependent isoleucine transport activity which was more than 30-fold higher than that of Kaback vesicles prepared from the same strains of E. coli K12. The isoleucine carrier activity of IM vesicles was inhibited by norleucine but not by threonine. The carrier was driven by proton motive force. Mutants were isolated which had lost the carrier activity for isoleucine, as judged by assay with IM vesicles. Using these mutants, the effects of binding proteins specific for branched chain amino acids on the translocation of substrate in IM vesicles were studied. Leucine-isoleucine-valine-threonine-binding protein (LIVT-binding protein) stimulated the initial rate of isoleucine uptake by IM vesicles only when the vesicles possessed carrier activity and it did not affect the Kt value for entry of substrate. The partial reconstitution of the osmotic shock-sensitive transport reaction is suggested in which the binding protein seems to affect the carrier activity with turnover ability.