Active Transport in Escherichia Coli From Membrane to Molecule

Lac permease of Escherichia coli: histidine-205 and histidine-322 play different roles in lactose/protein symport

“…It is apparent therefore that catalytically active permease will not tolerate replacement of His-322 with Arg, Asn, or Gin, and it follows that His-322 must play a different role than His-205 in the symport mechanism. Efflux, exchange, and counterflow are useful strategems for studying certain aspects of permease activity (Kaback 1983(Kaback , 1986aKaczorowski & Kaback, 1979), and the results shown in Figures 2 and 3 demonstrate that lac permease containing Arg in place of His-322 is grossly defective in each of these reactions. Thus, His-322 appears to be required for each translocation reaction catalyzed by the permease, regardless of whether or not net H+ movement is involved.…”

“…Preliminary support for certain aspects of the model has been obtained from proteolysis experiments and from binding studies with monoclonal antibodies against purified permease and site-directed polyclonal antibodies against synthetic polypeptides corresponding to domains that are presumably exposed on the surfaces of the membrane [cf. Kaback (1983Kaback ( , 1986a for reviews].Site-directed mutagenesis (Zoller & Smith, 1983) is currently being utilized to probe the structure and function of the permease, and it has been demonstrated that, out of a total of eight Cys residues, only Cys-154 appears to be important for active lactose transport (…”

“…Preliminary support for certain aspects of the model has been obtained from proteolysis experiments and from binding studies with monoclonal antibodies against purified permease and site-directed polyclonal antibodies against synthetic polypeptides corresponding to domains that are presumably exposed on the surfaces of the membrane [cf. Kaback (1983Kaback ( , 1986a for reviews].…”